New euselachian teeth from the Ladinian-Carnian interval of Guizhou and Yunnan Provinces, South China

New euselachian teeth from the Ladinian-Carnian interval of Guizhou and Yunnan Provinces, South China | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article New euselachian teeth from the Ladinian-Carnian interval of Guizhou and Yunnan Provinces, South China Siyan Zhao, Jiachun Li, Gilles Cuny, Zuoyu Sun This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7193674/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A taxonomic study of four tooth genera of euselachian sharks from the Ladinian-Carnian interval of the Guizhou and Yunnan Provinces, South China is presented. They include one euselachian shark of uncertain affinity, two indeterminate neoselachian sharks and one potential hexanchid shark. These four taxa display non-durophagous feeding behaviors, including grasping-swallowing, grasping, tearing and cutting strategies. High-resolution micro-CT scans reveal that both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 possess orthodont teeth. Euselachii gen. et sp. indet. exhibits a prominent longitudinal vascular canal but lacks an ascending pulp cavity, while Neoselachii gen. et sp. indet. 1 features two longitudinal vascular canals and a vascular cavity that ascends into the main cusp. Chondrichthyans Euselachii Vascular system Histology Triassic Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The Ladinian-Carnian ‘Falang’ Formation in southwestern Guizhou and eastern Yunnan Provinces consists of the Zhuganpo Member and Wayao Member in ascending stratigraphic order. It is renowned for yielding two marine vertebrate Lagerstätten that recorded exceptionally well-preserved marine reptiles and fishes, viz. the latest Ladinian Xingyi Fauna and the early Carnian Guanling Biota, respectively (Jiang et al., 2005 , 2023 ; Wang et al., 2008 ; Benton et al., 2013 ; Tintori et al., 2015 ; Lu et al., 2018 ; Fang et al., 2023 ). Although scarce in the fossil record, chondrichthyan remains from the Zhuganpo Member of Guizhou Province were documented in previous studies (Chen, 2002 ; Chen and Cuny, 2003 ; Chen et al., 2007 ; Zhang et al., 2012 ; Li et al., 2022 ). To date, nine tooth taxa have been identified in Guizhou Province. These include three hybodonts ( Omanoselache (‘ Polyacrodus ’) contrarius , ? Parvodus and ?Hybodontiformes) and one potential neoselachian (Neoselachii?) from Guanling County (Chen and Cuny, 2003 ; Chen et al., 2007 ). Additionally, a shark assemblage from Xingyi City (Nimaigu section) comprises two elasmobranchs with uncertain affinity (aff. Rosaodus sp. and Rosaodus xingyiensis ), two indeterminate euselachians (Euselachii gen. et sp. indet. and Favusodus orientalis ), and one synechodontiform shark ( Keichouodus nimaiguensis ) (Li et al., 2022 ). This fauna is dominated by sharks with a cladodont-like dentition and almost devoid of durophagous euselachians, which makes it different from all other contemporaneous shark faunas worldwide. Herein, we present nine newly founded euselachian teeth from the Zhuganpo Member of the ‘Falang’ Formation at the Nimaigu and Yize sections in South China. Both external tooth morphologies and internal dental vascular system have been described in detail. The study not only enhances our understanding of the diversity of the chondrichthyan assemblage from the ‘Falang’ Formation in South China, but also, for the first time, reveals the three-dimensional dental microstructure of Triassic chondrichthyan teeth. Geological setting The teeth described in the present study have been found in two sites, i.e. the Nimaigu section (25°09′52″N, 104°47′19″E) in Wusha Town, Xingyi City, southwestern Guizhou Province, and the Yize section (25°01'06.8"N, 104°27'56.1"E) in Changdi Town, Luoping County, Qujing City, eastern Yunnan Province, respectively (Fig. 1 A). During the Triassic, these two sampled sites were located on the southwestern part of the Yangtze Carbonate Platform. Because of the collision between the Yangtze and North China plates during the Ladinian, a large-scale regression occurred across much of the Yangtze (Yin, 1982 ). However, the studied area experienced a transgression caused by tectonic differentiation, as indicated by the stratigraphic succession that records an upward transition from shallow-water dolomite of the Yangliujing Formation to deep-water marl and nodular limestone of the Zhuganpo Member, and subsequently to the black shale and marl of the Wayao Member that represents the maximum flooding surface (Enos et al., 1998 ; Li et al., 2005 ). At the Nimaigu section, a continuous stratigraphic succession spanning from the uppermost Yangliujing Formation to the basal part of the Wayao Member of the ‘Falang’ Formation is well-exposed through research excavations (Lu et al., 2018 ) (Fig. 1 B). Therein, the Ladinian-Carnian interval is constrained by the early Carnian Trachyceras ammonoid beds, which occur between layers 197 and 238, and by an LA-ICP-MS U-Pb zircon age of 239.8 ± 1.7 Ma of the layer 161 (Zou et al., 2015a ; Li et al., 2016 ). The lithology and stratigraphy of the Nimaigu section are described in detail by Ma et al. ( 2013 ), Zou et al. ( 2015a /b), Li et al. ( 2016 ), Lu et al. ( 2018 ) and Chai et al. ( 2019 ). The Yize section is a newly excavated Ladinian-Carnian section that is laterally correlated to the Niamigu section. It consists of the Zhuganpo Member and the overlying Wayao Member, and five conodont zones have been established therein, viz. in ascending order: the Paragondolella inclinata Zone, the Quadralella polygnathiformis Zone, the Quadralella praelindae Zone, the Quadralella auriformis Zone and the Quadralella robusta Zone. The Ladinian-Carnian interval is constrained by the first occurrences of the conodonts Quadralella polygnathiformis and Quadralella intermedia within the Zhuganpo Member (Zhang and Sun, 2023 ). Materials and methods During the fieldwork in 2017, 2018 and 2019, we collected large amounts of rock samples from the ‘Falang’ Formation at the Nimaigu and Yize sections. These samples were broken into fragments approximately 4 cm in size and subsequently dissolved using 10% acetic acid. Conodont and chondrichthyan fossils were then manually picked from the residues under a stereomicroscope. This study examined a total of nine shark teeth: GMPKU-P-4268 from the Yize section, and GMPKU-P-4261-4267, 4269 from the Nimaigu section. They were photographed using a JEOL JCM-6000 Plus scanning electron microscope (SEM) under an acceleration voltage of 10 kV at the School of Earth and Space Sciences, Peking University. The specimens GMPKU-P-4263 and GMPKU-P-4266 were scanned using a SkyScan 1172 micro-CT device at the State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences. Micro-CT scanning was performed with a 180° rotation, a rotation step of 0.2° and a pixel size of 0.56 µm. The source voltage and current were set to 48 kV and 200 mA, respectively. The teeth and their vascular system were three-dimentionally reconstructed using Avizo 2022.2. All specimens are housed in the Geological Museum of Peking University (GMPKU), Beijing, China. Systematic palaeontology The systematic framework and tooth morphological terminology follow Ginter et al. ( 2010 ), Thies et al. ( 2014 ) and Cappetta ( 2012 ). Dental histological terminology follows Jambura et al. ( 2020 ). The vascular terminology follows Ivanov ( 2022 ), and Ivanov and Duffin ( 2024 ). Class Chondrichthyes Huxley, 1880 Subclass Elasmobranchii Bonaparte, 1838 Cohort Euselachii Hay, 1902 Euselachii gen. et sp. indet. Figures 2 and 3 Referred specimens Five isolated teeth, GMPKU-P-4261-4265. Locality and horizon Nimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layers 79, 84, 146, 152–153 and 186, Zhuganpo Member, Falang Formation (late Ladinian, Middle Triassic). Description of morphological characteristics The teeth are elongated mesiodistally and narrow labiolingually. All teeth are broken, measuring 0.21–0.37 mm in height, 0.15–0.28 mm labio-lingually and 0.58–1.10 mm mesio-distally. A gradient monognathic heterodonty is characterized by anterolateral teeth with arched root and relatively separated cusps, whereas posterolateral teeth display a straight root and fused cusps. The crown possesses a main cusp flanked by 2 to 4 lateral cusplets on each side, without any intermediate cusplets. The main cusp is robust and pyramidal (Fig. 2 R). The lateral cusplets decrease in height laterally (Fig. 2 A, 2 U), with the highest being always lower than the main cusp. One or two intermediate cusplets are usually present between the main cusp and the first pair of lateral cusplets (Fig. 3 F, 2 P). These intermediate cusplets are significantly smaller than lateral ones. The mesial and distal extremities of the crown sometimes display a small protuberance or accessory cusplet, which protrudes obliquely from the outermost lateral cusplet (Fig. 2 P, 2 U). All cusps are inclined distally and curved lingually (Fig. 2 P, 2 O). The adjacent cusps are well-separated by V-shaped notches on the anterolateral teeth (Fig. 2 A), whereas they are fused at their base on the posterolateral teeth (Fig. 2 U). In apical view, each cusp presents an acute apex where the mesial and distal cutting edges converge (Fig. 2 U). The main cusp and some lateral cusplets exhibit a prominent triangular protrusion on the labial and/or lingual side, whose apex is connected to that of the corresponding cusp by a ridge (Fig. 2 C, 2 F, 3 E). There are 1 to 2 vertical ridges on the upper part of the cusp when no triangular protrusion is present (Fig. 2 K, 2 P). The crown of GMPKU-P-4263 displays eight mesiodistally compressed humps, which either connect with an overlying ridge (Fig. 2 K, 2 L) or lie on the lower part of the triangular protrusion (Fig. 3 B, 3 D, 3 E). The crown-root junction displays a distinct incision lingually, but it is not well marked labially (Fig. 3 A, 3 E). The root of GMPKU-P-4263 is relatively well preserved. It is low and rectangular (Fig. 2 N), protruding labially and lingually, although the labial protrusion is significantly less developed. There is a row of small foramina on the labial root face (Fig. 2 K). Foramina on the lingual face of the root are more randomly distributed than those on the labial one. The basal face of the root is flat and presents several small to large foramina, which are restricted to the labial part (Fig. 3 C). The vascularization is anaulacorhize. Description of internal structure The crown consists of enameloid and a compact layer of underlying orthodentine (Fig. 3 F). The orthodentine enfolds a large longitudinal vascular canal (pulp cavity?) at the crown-root junction. However, no ascending pulp cavity can be seen (Fig. 3 F, 3 H). Osteodentine is restricted to the root (Fig. 3 H). Therefore, the histotype is orthodont. The vascular system consists of a longitudinal vascular canal, a vascular canal plexus, connective vascular canals and ascending vascular canals. The longitudinal vascular canal is cylindrical, with a diameter ranging from 30 to 90 µm. It extends along the crown-root junction and almost reaches the mesial and distal extremities of the root (Fig. 3 I). At the distal extremity, the longitudinal canal branches into three thinner canals (Fig. 3 V). The single-layered vascular plexus consists of interconnected canals ranging from 8 to 40 µm in diameter, forming numerous circular grids (Fig. 3 U). The vascular plexus extends both labially and lingually, terminating as foramina on the corresponding root faces (Fig. 3 O, 3 P, 3 T). The meshed vascular plexus connects to the overlying longitudinal vascular canal through short connective vascular canals (Fig. 3 N, 3 O) and connects to the underlying ascending vascular canals (Fig. 3 R, 3 U). Remarks The material is reminiscent of an indeterminate euselachian from the late Ladinian (Middle Triassic) of the same locality (Li et al, 2022 ). They share a similar pattern of monognathic heterodonty, cladodont-like crown, pyramidal main cusp, labially and lingually protruding root and anaulacorhize vascularization. However, the teeth described herein differ from Euselachii gen. et sp. indet. in Li et al., 2022 by having significantly more developed labial and lingual triangular protrusions on the main cusp and lateral cusplets. Additionally, a presumed posterior tooth of ?Hybodontidae from the early Carnian of Guanling, Guizhou, also shows a labial triangular protrusion on the main cusp, intermediate cusplets between main cusp and lateral cusplets, well-defined cusps, incised crown-root junction and arched root with both labial and lingual foramina (Chen and Cuny, 2003 ). The presence of intermediate cusplets in our materials, as well as in the tooth from Guanling, do not fit the typical crown morphology of Hybodontiformes, which normally displays a gradually decreasing height of the cusps (Ginter et al., 2010 ; Koot et al., 2015 ). We tentatively assign our material to a taxon that is closely allied, if not identical, to the Euselachii gen. et sp. indet. of Li et al. ( 2022 ) and ?Hybodontidae indet. of Chen and Cuny ( 2003 ). Subcohort Neoselachii Compagno, 1977 Order incertae sedis Neoselachii gen. et sp. indet. 1 Figures 4 Referred specimens One broken tooth, GMPKU-P-4266 Locality and horizon Nimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layers 145-146, Zhuganpo Member, ‘Falang’ Formation (late Ladinian, Middle Triassic). Description of morphological characteristics The tooth measures 0.75 mm in height, 0.53 mm labio-lingually and 1.43 mm mesio-distally. The crown displays a robust main cusp flanked by one lateral cusplet on the mesial side and two lateral cusplets on the distal side. The main cusp is biconvex, curved lingually and slightly inclined distally (Figure 4A, 4E). Its cutting edges are well developed and connected to adjacent lateral cusplets (Figure 4C). The lateral cusplets are broken. The labial face of the main cusp is devoid of ornamentation (Figure 4A). Lingually, there are 7 faint vertical ridges with varying lengths (Figure 4B). The crown-root junction shows a slight incision labially, but it is not well marked on the lingual side (Figure 4F, 4G). The root is low (no more than 30% of the height of the tooth), and kidney-shaped in basal view (Figure 4G, 4H). It protrudes lingually and swells at the middle part of the root (Figure 4I, 4J). The root is slightly arched on the labial side but remains straight on the lingual side (Figure 4F, 4G). The distal and mesial extremities of the labial face of the root displays 3 and 4 foramina, respectively (Figure 4F). Lingually, the root exhibits two rows of foramina. The upper row has 8 small to moderate foramina that are located near the crown-root junction, whereas the lower row consists of 4 larger foramina, situated in the central part of the lingual face of the root (Figure 4G, 4J). The basal face of the root shows numerous randomly distributed foramina with varying sizes. A mesio-distal depression is present on the labial part of the basal face of the root, which contains a row of foramina accompanied by very short unroofed canals (Figure 4H). The vascularization may represent a transitional state between anaulacorhize and polyhemiaulacorhize. Description of internal structure The crown is composed of an outer enameloid and inner orthodentine layer, which encases a reduced pulp cavity ascending within the main cusp (Figure 4K). The orthodentine is compact with a high density (Figure 4K, 4M). Some deposits of medium to low density are distributed in the central area of the main cusp and within the cavities (Figure 4K, 4L, 4M). Osteodentine is confined to the root and does not invade the pulp cavity (Figure 4K, 4M). Therefore, the tooth histotype is orthodont. The vascular system contains two longitudinal vascular canals, connective vascular canals, a pulp cavity, main transverse vascular canals, secondary transverse vascular canals and ascending vascular canals. The two longitudinal vascular canals are 130 to 150 μm in diameter and nearly the same mesio-distal length as the tooth (Figure 4N, 4O). The upper and lower longitudinal vascular canals are interconnected by several short vertical or oblique connective vascular canals (Figure 4R, 4S). The upper longitudinal vascular canal is interconnected with a small pulp cavity above (Figure 4Q). There are four parallel main transverse vascular canals in the middle of the root, with diameters ranging from 52 to 93 μm. The main transverse vascular canals run labiolingually from the lingual face of the root and terminate in the basal depression (Figure 4O, 4U, 4V). They connect to the overlying longitudinal vascular canals through a few short connective canals (Figure 4W). The secondary transverse vascular canals are shorter and narrower than the main transverse vascular canals (Figure 4V, 4W). The main and secondary transverse vascular canals are sometimes interconnected by short connective vascular canals (Figure 4U). A main transverse vascular canal and two secondary vascular canals extend labially from the middle part of the lower longitudinal vascular canal and are interconnected at their extremities by two longitudinal connective vascular canals, without opening externally. The ascending vascular canals are short and interconnected with transverse vascular canals. They open on both apical and basal faces of the root (Figure 4O, 4U). In addition to the vascular canals, there are long, narrow and randomly extended irregular canals, likely a result of microbial activity (Underwood et al., 1999; Cappetta, 2012). They are primarily distributed around the pulp cavity (Figure 4X) and may open on the root surface (Figure 4X, 4Y). Remarks GMPKU-P-4266 resembles Rosaodus , a cladodont-like shark from the late Ladinian of the Nimaigu section (Li et al., 2022), with a conical and lingually curved main cusp, a labially depressed basal root and a swollen lingual root. However, it differs from Rosaodus by possessing radially arranged ridges on the lingual face of the main cusp, large foramina in the depression of the basal face of the root and double rows of foramina on the lingual face of the root. Additionally, the well-defined high main cusp and lingually displaced root with a basal labial depression where some foramina open, are reminiscent of two Anisian Neoselachii: Mucrovenator and Rhomaleodus (Cuny et al., 2001; Andreev and Cuny, 2012). However, GMPKU-P-4266 exhibits an unornamented labial crown face and two rows of foramina on the lingual root face, whereas the labial crown face of Mucrovenator and Rhomaleodus are both ornamented with vertical ridges, and the lingual face of the root displays only a single row of foramina. Besides, the imperforate labial root face and flat crown-root junction of Mucrovenator , and the bifurcated ridges and constricted crown-root transition of Rhomaleodus also differ from those of GMPKU-P-4266. These differences therefore preclude assigning GMPKU-P-4266 to Mucrovenator or to Rhomaleodus . Nevertheless, its vascularization displaying large foramina openings in the mesiodistal depression on the basal face of the root points to an affinity with Neoselachii. Neoselachii gen. et sp. indet. 2 Figure 5 Referred specimens One anterior tooth, GMPKU-P-4267 Locality and horizon Nimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layer 186, Zhuganpo Member, ‘Falang’ Formation (late Ladinian, Middle Triassic). Description of morphological characteristics The tooth measures 0.56 mm mesiodistally, 0.37 mm labiolingually and 0.68 mm in height. The crown bears a slender main cusp without lateral cusplet. The main cusp displays two sharp cutting edges laterally (Figure 5E) and a keel-like protrusion on the lower part of its lingual face. It is strongly biconvex, curved lingually and slightly inclined distally (Figure 5B, 5E). The crown has no ornamentation. The root is low and consists of two symmetrical lobes. The lobes are triangular, flattened and elongated mesiodistally in apical and basal views (Figure 5C, 5D). They lean downward at an angle of approximately 45°, giving the root an inverted V-shaped outline in labial and lingual views (Figure 5A, 5B). The central part of the lingual face of the root is swollen and partly separated by a nutritive canal forming a large foramen (Figure 5C). The basal root face is flat and shows an unroofed median canal on the lingual part (Figure 5D). The root vascularization reminds therefore of a hemiaulacorhize type. Remarks GMPKU-P-4267 reminds of an undetermined neoselachian shark from the Ladinian-Carnian interval of Guanling, Guizhou Province (Chen et al., 2007). They share a slender and lingually curved main cusp, unornamented crown, V-shaped and triangular root with a lingually unroofed median canal. However, the tooth from Guanling exhibits a pair of lateral cusplets on the crown, several foramina on the lingual face of the root lobes and a labially incised crown-root junction (Chen et al., 2007: Figs. 4A, 4D). These differences may be explained by some heterodonty pattern (monognathic, dignathic, gynandric or ontogenetic), but with only two teeth recovered so far, no pattern can be demonstrated. Besides, the tooth from Guanling displays a less roofed median canal on the basal face of the root (Chen et al., 2007: Fig. 4C), perhaps resulting from intraspecific variation. However, the tooth from Guanling (6 mm mesiodistally) is significantly larger than the tooth from Xingyi (0.56 mm mesiodistally), yet the size data for the former do not correspond to the scales shown in the plate (Chen et al., 2007: Figs. 4A-4D). Therefore, the specimens from Xingyi and Guanling could belong to the same species. At the minimum, they are closely related. In accordance with Chen et al. (2007), we assign GMPKU-P-4267 to the Neoselachii based on its hemiaulacorhize-like vascularization. Based on the presence of a well-developed median lingual protuberance and median vascular canal, Chen et al. (2007) proposedthat the Guanling specimen might be closely related to the Palaeozoic Neoselachii Cooleyella , which has been recovered from the Mississippian to the Guadalupian (Ivanov and Duffin, 2024). However, Cooleyella displays one or two foramina on the basal face of the root (Duffin and Ward, 1983; Duffin et al., 1996; Ivanov and Duffin, 2024), which is not the case in the Chinese specimens from Xingyi and Guanling. The slender, conical main cusp, bilobate root with a flat basal face showing a partially roofed median canal, and a central foramen on the lingual root of the Chinese material, are reminiscent of the teeth of certain Scyliorhinidae, such as Apristurus laurussonii and Pseudoscyliorhinus reussi (Herman et al., 1990; Underwood and Ward, 2008; Cappetta, 2012). However, the root lobes of the Chinese specimens are extending downward and labially aligned, whereas those of Scyliorhinidae are coplanar and labially displaced. In addition, the unornamented crown, non-porous labial root lobes and the absence of labial root protrusion also preclude the attribution of GMPKU-P-4267 to the Scyliorhinidae. Superorder Squalomorphii? Compagno, 1973 Order Hexanchiformes? de Buen, 1926 Family Hexanchidae? Gray 1851 Hexanchidae? gen. et sp. indet. Figure 6 Referred specimens Two isolated teeth, GMPKU-P-4268 and 4269. Locality and horizon Nimaigu village, Wusha Town, Xingyi City, Guizhou Province, China; Layers 145-146, Zhuganpo Member, ‘Falang’ Formation (late Ladinian, Middle Triassic). Changdi Township, Luoping County, Qujing City, Yunnan Province; Zhuganpo Member, ‘Falang’ Formation (early Carnian, Late Triassic). Description of morphological characteristics The broken teeth measure 1.18-1.33 mm mesiodistally, 0.22-0.25 mm labiolingually and 0.68-1.47 mm in height. The crown is compressed labiolingually (Figure 6J). It bears a triangular main cusp flanked by three pairs of smaller lateral cusplets. The lateral cusplets on each side of the main cusp decrease in height laterally, and the outmost pair of cusplets is much reduced (Figure 6F). All cusps are distally inclined and separated by V-shaped notches. The cutting edges of the cusps are well developed and interconnected. No ornamentation is present on the crown. The base of the crown, or the possible uppermost part of the root, protrudes slightly toward the lingual side (Figure 6I, 6J). Remarks GMPKU-P-4268 and 4269 resemble teeth of Hexanchidae because of their labiolingually compressed crown, distally inclined triangular cusps comprising a main cusp flanked by smaller lateral cusplets whose height decreases laterally (Cappetta, 2012; Cappetta and Grant-Mackie, 2018). These teeth are also comparable to Hexanchidae gen. et sp. indet. from the late Permian of Japan and ? paranotidanus sp. from the middle Jurassic of England (Underwood and Ward, 2004; Burrow et al., 2008). However, the root is missing in our material, which makes it difficult to ascribe it to Hexanchidae with certainty, and more complete specimens are needed to determine their affiliation. Here, we tentatively assign them to Hexanchidae considering their crown morphology. Discussion Biostratigraphy and Palaeoecology Stratigraphically, one tooth of Hexanchidae? gen. et sp. indet. (GMPKU-P-4269) is recovered from layers 145-146 of the Zhuganpo Member of the ‘Fanglang’ Formation at the Nimaigu section (late Ladinian, Zou et al., 2015a). The age of layers 145-146 were considered to be the late Ladinian that below the early Carnian Trachyceras beds (Zou et al., 2015a) (Figure 1B). Another tooth of Hexanchidae? gen. et sp. indet. (GMPKU-P-4268) is collected from the Zhuganpo Member of the ‘Fanglang’ Formation at the Yize section, present above the first occurrences of conodonts Quadralella polygnathiformis and Quadralella intermedia at this section (early Carnian, Zhang and Sun, 2023). Nevertheless, their biostratigraphic frameworks were established using different fossil groups (ammonoid zones in the Nimaigu section versus conodont zones in the Yize section). Whether these two sections are completely synchronous requires further verification through detailed stratigraphic measurements and microfacies analysis. The remaining three taxa are distributed between layers 79 and 186 exclusively at the Nimaigu section, occurring from the late Ladinian Haoceras xingyiense Zone but not extending into the early Carnian Trachyceras beds (Zou et al., 2015a) (Figure 1B). Therefore, Hexanchidae? gen. et sp. indet. is the only taxon may across the Ladinian-Carnian boundary, whereas the remaining three taxa are confined to the late Ladinian. Six chondrichthyan taxa previously described from the Nimaigu section include Elasmobranchii incertae sedis (aff. Rosaodus sp., Rosaodus xingyiensis ), Euselachii (Euselachii gen. et sp. indet., Favusodus orientalis , Keichouodus nimaiguensis ), and a possible Holocephali (aff. Arctacanthus sp.) (Li et al., 2022). The chondrichthyan teeth described in this study add three new euselachians: Neoselachii gen. et sp. indet. 1, Neoselachii gen. et sp. indet. 2 and Hexanchidae? gen. et sp. indet., and possibly a fourth one, Euselachii gen. et sp. indet., so that at least nine chondrichthyan taxa have been found from the Nimaigu section. From a paleogeographic point of view, the four chondrichthyans described herein are endemic taxa unknown outside South China. The newly described Euselachii gen. et sp. indet. has a grasping-swallowing dentition with cladodont-like crowns. It displays stronger protrusions of the crown than those of the previously reported Euselachii gen. et sp. indet (Li et al., 2022). Neoselachii gen. et sp. indet. 1 exhibit grasping type tooth characterized by a conical main cusp flanked by lateral cusplets, whereas Neoselachii gen. et sp. indet. 2 displays tearing type tooth featuring a slender main cusp with sharp cutting edges. Hexanchidae? gen. et sp. indet. exhibits an extensively labio-lingually compressed crown with triangular cusps, indicative of cutting-type teeth (Cappetta, 2012). Consequently, the newly described taxa possess grasping-swallowing, sharp-grasping and cutting-type dentition and support previous observations that the shark fauna from Nimaigu section lacks durophagous forms (Li et al., 2022), which makes it different from other Ladinian-Carnian shark assemblages that were predominantly represented by durophagous sharks (Chen et al., 2007; Pla et al., 2013; Manzanares et al., 2018; Manzanares et al., 2020). Dental histology The dental histology of Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 was examined using micro-CT scanning, allowing three-dimensional reconstruction. The dental histology of Neoselachii gen. et sp. indet. 2 and Hexanchidae? gen. et sp. indet. is not presented due to artificial damage and poor preservation. The crown dentine of both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 consists entirely of compact orthodentine, which enfolds the pulp cavity. An ascending pulp cavity is present within the main cusp of Neoselachii gen. et sp. indet. 1, indicating it is a typical orthodont tooth, whereas no ascending pulp cavity is observed in Euselachii gen. et sp. indet.. Porous osteodentine is present only in the root of these two taxa, which is illustrated by a dense network of vascular canals, including connective vascular canals and ascending vascular canals. However, Euselachii gen. et sp. indet. exhibits a single longitudinal vascular canal associated with a vascular plexus, whereas Neoselachii gen. et sp. indet. 1 possesses two longitudinal vascular canals and numerous transverse vascular canals. The non-neoselachian euselachian sharks comprise Hybodontiformes, Protacrodontoidea, Sphenacanthidae and some euselachians with uncertain affinities. Investigations focusing on the dental histology of hybodont sharks are comparatively abundant (e.g., Seilacher, 1943; Patterson, 1966; Johnson, 1981; Maisey, 1983; Heckert et al., 2007; Stumpf et al., 2021; Cicimurri et al., 2024). There are osteodont (e.g., Tribodus limae , Lane and Maisey, 2012), pseudoosteodont (e.g., Lissodus minimus , Patterson, 1966; Crassodus reifi , Maisch and Matzke, 2016) and orthodont (e.g., Palaeobates angustissimus , Patterson, 1966; Lissodus sardiniensis ,Fischer et al., 2010) histotypes in hybodont sharks. Sometimes, both pseudoosteodont and orthodont histotypes may occur within the same hybodont species (Błażejowski, 2004). Comparatively, studies on dental histology of other non-neoselachian euselachian sharks remain scarce, and only osteodont and orthodont histotypes have been described so far (e.g., Ivanov et al., 2017; Ivanov et al., 2022; Ivanov, 2022). The Euselachii gen. et sp. indet. described here exhibits an orthodont tooth characterized of a large longitudinal vascular canal, rather than a pulp cavity/pulp cavities that run vertically in most orthodont teeth. A longitudinal vascular canal is also present in Gzhelodus serratus (Protacrodontoidea, Euselachii) from the Late Carboniferous of Russia (Ivanov, 2022). Characterized by high, basally fused cusps, it lacks an ascending pulp cavity but exhibits a moderately developed longitudinal vascular canal accompanied by a few “dental tubules”. However, Gzhelodus serratus distinguishes itself from Euselachii gen. et sp. indet. by containing numerous transverse vascular canals. Another euselachian taxon, Desinia radiata (Sphenacanthidae, Euselachii) from the Middle-Late Permian of Russia, also possess longitudinal vascular canals (Ivanov et al., 2022). It has a high main cusp flanked by well-separated cusplets. However, it exhibits two slender longitudinal vascular canals, of which the upper one connects to a pulp cavity that extends to the top of the main cusp. Additionally, orthodont hybodont teeth with flat crown possesses a thick longitudinal vascular canal and lacks ascending pulp cavity as well (e.g., Palaeobates angustissimus , Böttcher, 2024). The multicuspid teeth of the hybodont shark Lamarodus triangulus , characterized by low and bulky cusps, also features a large longitudinal vascular canal, yet lacks an ascending pulp cavity (Ivanov et al., 2020). In summary, the presence of a longitudinal vascular canal, unaccompanied by one or more ascending pulp cavities, seems to be independent of crown morphology. In neoselachian sharks, orthodont, pseudoosteodont and osteodont histotypes are present, and the pseudoosteodont histotype is the most widespread in extant sharks and believed to be the plesiomorphic condition (Moyer et al., 2015; Schnetz et al., 2016; Mollen and Hovestadt, 2018; Jambura et al., 2020, Malyshkina et al., 2020). GMPKU-P-4266 exhibits a baso-labial depression where several unroofed canals are present, reminiscent of the polyhemiaulacorhize vascularization characteristic of Synechodontiformes (Klug, 2010). The dental histology of Synechodontiformes is poorly understood, with studies limited to Romphaidon , Synechodus and Wimanodon (Mollen and Hovestadt, 2018; Jambura et al., 2020; Saugen et al., 2024). Romphaidon and Wimanodon exhibit a pseudoosteodont histotype, whereas both orthodont and pseudoosteodont histotypes are known to coexist within the genus Synechodus (Mollen and Hovestadt, 2018; Jambura et al., 2020; Saugen et al., 2024). GMPKU-P-4266 displays an orthodont histotype with an ascending pulp cavity within the main cusp. Its vascular system resembles that of Synechodus sp. from the Early Cretaceous of northern France, as both share the presence of longitudinal vascular canal, ascending pulp cavity, and transverse vascular canals (Mollen and Hovestadt, 2018). However, compared with GMPKU-P-4266, the longitudinal vascular canal of Synechodus sp. is significantly narrower, and only a single longitudinal vascular canal is present. Besides, the meshed secondary vascular canals of Synechodus sp. are not present in Neoselachii gen. et sp. indet. 1. Additionally, the polyhemiaulacorhize vascularization of Synechodontiformes is defined by the presence of unroofed canals within the labial depression on the basal face of the root (Klug, 2010; Cappetta, 2012). The detailed illustration and description of the three-dimensional vascular system in Synechodontiformes is helpful for a comprehensive understanding of this type of root vascularization. Conclusion Four endemic euselachian sharks comprising Euselachii gen. et sp. indet., Neoselachii gen. et sp. indet. 1, Neoselachii gen. et sp. indet. 2, and Hexanchidae? gen. et sp. indet. are described from the Ladinian-Carnian interval of the Zhuganpo Member, ‘Falang’ Formation in Guizhou and Yunnan Provinces. In the study, Hexanchidae? gen. et sp. indet. represent the only taxon may across the Ladinian-Carnian boundary, whereas Euselachii gen. et sp. indet. and both Neoselachii gen. et sp. indet. 1 and 2 are confined to the late Ladinian. Palaeoecologically, Euselachii gen. et sp. indet. exhibits grasping-and-swallowing dentition; Neoselachii gen. et sp. indet. 1 and 2 exhibit grasping type and tearing type tooth, respectively; and Hexanchidae? gen. et sp. indet. bears teeth adapted for cutting. These findings further confirm that the Ladinian-Carnian shark assemblage at the Nimaigu section was dominated primarily by non-durophagous sharks. From a histological point of view, both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 display an orthodont histotype. Euselachii gen. et sp. indet. possesses a large longitudinal vascular canal but lacks an ascending pulp cavity. This feature also occurs in hybodonts with both flat crowns and multicuspid crowns bearing well-developed cusps, suggesting that its presence may be independent of tooth morphology. Neoselachii gen. et sp. indet. 1 displays a vascularization somewhat similar to the polyhemiaulacorhize type of synechodontiform sharks; however, its internal vascular architecture differs from that of the Cretaceous Synechodus sp. by the presence of two large longitudinal vascular canals. Declarations Acknowledgement The authors would like to thank Chai Jun (Lecturer, Beijing City University), Liu Shuang (Assistant Researcher, National Natural History Museum of China), Yin Yalei (Lecturer, Shenyang Normal University), Dai Yanlin (PetroChina Kunlun Gas Co., Ltd. Beijing Branch) and Tetsuya Sato for their assistance in collecting rock samples; Xu Xiuping (staff of the Plant Science Facility of the Institute of Botany, Chinese Academy of Sciences) for conducting the micro-CT scanning of the samples, as well as Wang Mingcui for dissolving the rock samples and picking shark remains in the laboratory. Author contributions ZS and JL organized and designed of the study; ZS and JL conducted field work and collected samples; SZ, JL and GC identified the fish remains and wrote the manuscript; SZ analysed CT data and reconstructed dental histology, All authors revised the paper. Funding This study was financially supported by the National Natural Science Foundation of China (42172009, 41920104001), China Geological Survey (121201102000150012-09) and Natural Science Basic Research Program of Shaanxi (2025JC-YBQN-409). Availability of data and materials The micro-CT data and project files used in this study are available from the corresponding author upon reasonable request. Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests. References Andreev, P. S., & Cuny, G. (2012). New Triassic stem selachimorphs (Chondrichthyes, Elasmobranchii) and their bearing on the evolution of dental enameloid in Neoselachii. Journal of Vertebrate Paleontology , 32(2): 255-266. https://doi.org/10.1080/02724634.2012.644646 Benton, M. J., Zhang, Q. Y., Hu, S. Z., Chen, Z. Q., Wen, W., Liu, J., Huang, J. Y., Zhou, C. Y., Xie, T., Tong, J. N., & Choo, B. (2013). Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass extinction. Earth - Science Reviews , 125, 199-243. https://doi.org/10.1016/j.earscirev.2013.05.014 Błażejowski, B. (2004). Shark teeth from the Lower Triassic of Spitsbergen and their histology. Polish Polar Research , 25(2): 153-167. Böttcher, R. (2024). Root resorption during tooth replacement in sharks-a unique character of the Hybodontiformes (Chondrichthyes, Elasmobranchii). Palaeodiversity , 17(1): 121-194. https://doi.org/10.18476/pale.v17.a6 Bonaparte, C. L. J. (1838). Selachorum tabula analytica. Nuovi Annali delle Scienze Naturali Bologna , 1: 195-214. Burrow, C. J., Hovestadt, D. C., Hovestadt-Euler, M., Turner, S., & Young, G. C. (2008). New information on the Devonian shark Mcmurdodus , based on material from western Queensland, Australia. Acta Geologica Polonica , 58(2): 155-163. Cappetta, H. (2012). Chondrichthyes. Mesozoic and Cenozoic Elasmobranchii: teeth. In Schultze H.P. (Ed.), Handbook of Paleoichthyology (Volume 3E). München: Friedrich Pfeil. Cappetta, H., & Grant-Mackie, J. (2018). Discovery of the most ancient Notidanodon tooth (Neoselachii: Hexanchiformes) in the Late Jurassic of New Zealand. New considerations on the systematics and range of the genus. Palaeovertebrata , 42(1). https://doi.org/10.18563/pv.42.1.e1 Chai, J., Ni, P. G., Zhou, M., Lu, H., Sun, Z. Y., & Jiang, D. Y. (2019). Palaeoenvironment analysis of the Lower Fossil Assemblage of Middle Triassic Xingyi Fauna, Xingyi City, Guizhou Province. Journal of Stratigraphy , 43(3): 29-42 (in Chinese with English abstract). https://doi.org/10.19839/j.cnki.dcxzz.2019.03.003 Chen, L. D. (2002). New data of Middle-Late Triassic elasmobranch ichthyoliths from “Falang Formation” in Guanling, Guizhou. Acta Micropalaeontologica Sinica , 19: 276-287 (in Chinese with English abstract). Chen, L. D., & Cuny, G. (2003). Discovery of the Middle-Late Triassic elasmobranch ichthyoliths from Guanling area, Guizhou, SW China. Geological Bulletin of China ,22(4): 236-247. Chen, L. D., Cuny, G., & Wang, X. F. (2007). The chondrichthyan fauna from the Middle-Late Triassic of Guanling (Guizhou Province, SW China). Historical Biology , 19(4): 291-300. https://doi.org/10.1080/08912960701248234 Cicimurri, D., Ciampaglio, C., Hoenig, M., Shell, R., Fuelling, L., Peterman, D., Cline, D. A., & Jacquemin, S. (2024). A description of the new hybodont shark genus, Columnaodus , from the Burlington and Keokuk Limestones (Carboniferous, Mississippian, Osagean) of Illinois and Iowa, USA. Diversity , 16(5): 276. https://doi.org/10.3390/d16050276 Compagno, L. J. V. (1973). Interrelationships of living elasmobranchs. Zoological Journal of the Linnean Society , 53: 15-61. Compagno, L. J. V. (1977). Phyletic relationships of living sharks and rays. American Zoologist , 17(02): 303-322. Cuny, G., Rieppel, O., & Sander, P. M. (2001). The shark fauna from the Middle Triassic (Anisian) of north-western Nevada. Zoological Journal of the Linnean Society , 133(3): 285-301. https://doi.org/10.1006/zjls.2000.0273 de Buen, F. (1926). Catálogo ictiológico del Mediterráneo español y de Marruecos, recopilando lo publicado sobre peces de las costas mediterránea y próximas del Atlántico (Mar de España). In de Buen, O. (Ed.), Resultados de las campañas realizadas por acuerdos internacionales (Núm. 2). Spain: Instituto Español de Oceanografía. Duffin, C. J., & Ward, D. J. (1983). Neoselachian sharks' teeth from the Lower Carboniferous of Britain and the Lower Permian of the U.S.A. Palaeontology , 26(1): 93-110. Duffin, C. J., Richter, M., & Neis, P. A. (1996). Shark remains from the late Carboniferous of the Amazon Basin, Brazil. Neues Jahrbuch für Geologie und Paläontologie , Monatshefte , 4: 232-256. https://doi.org/10.1127/njgpm/1996/1996/232 Enos, P., Wei, J. Y., & Lehrmann, D. J. (1998). Death in Guizhou—Late Triassic drowning of the Yangtze carbonate platform. Sedimentary Geology , 118(1-4): 55-76. https://doi.org/10.1016/S0037-0738(98)00005-0 Fang, G. Y., Sun, Y. L., Ji, C., & Wu, F. X. (2023). First record of Saurichthys (Actinopterygii: Saurichthyidae) from the Late Triassic of eastern Paleo-Tethys. Vertebrata PalAsiatica , 61(1): 1-16. https://doi.org/10.19615/j.cnki.2096-9899.221013. Fischer, J., Schneider, J. W., & Ronchi, A. (2010). New hybondontoid shark from the Permocarboniferous (Gzhelian-Asselian) of Guardia Pisano (Sardinia, Italy). Acta Palaeontologica Polonica , 55(2): 241-264. http://dx.doi.org/10.4202/app.2009.0019 Ginter, M., Hampe, O., & Duffin, C.J. (2010). Chondrichthyes (Paleozoic Elasmobranchii: teeth). In H.P. Schultze (Ed.), Handbook of Paleoichthyology (Volume 3D). München: Friedrich Pfeil. Gray, J. E. (1851). List of the Specimens of Fish in the Collection of the British Museum : Part I ., Chondropterygii . London: Printed by order of the Trustees, British Museum. Hay, O. P. (1902). Bibliography and catalogue of the fossil vertebrate of North America. Bulletin of the United States Geological Survey , 179: 1-868. Heckert, A. B., Ivanov, A., & Lucas, S. G. (2007). Dental morphology of the hybodontoid shark Lonchidion humblei Murry from the Upper Triassic Chinle Group, USA. New Mexico Museum of Natural History and Science Bulletin , 41: 45-48. Herman, J., Hovestadt-Euler, M., & Hovestadt, D. C. (1990). Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living superspecific taxa of chondrichthyan fishes. Part A: Selachii. No. 2b: Order: Carcharhiniformes-Familiy: Scyliorhinidae. Bulletin de l’Institut royal des Sciences naturelles de Belgique , Biologie , 60: 181-230. Huxley, T. H. (1880). On the application of the laws of evolution to the arrangement of the Vertebrata, and more particularly of the Mammalia. Proceedings of the Zoological Society of London , 1880: 649-662. Ivanov, A. O. (2022). New late Carboniferous chondrichthyans from the European Russia. Bulletin of Geosciences , 97(2): 219-234. https://doi.org/10.3140/bull.geosci.1845 Ivanov, A. O., & Duffin, C. J. (2024). Late Palaeozoic anachronistid chondrichthyans. Historical Biology , 1-19. https://doi.org/10.1080/08912963.2024.2388208 Ivanov, A. O., Duffin, C. J., & Naugolnykh, S. V. (2017). A new euselachian shark from the early Permian of the Middle Urals, Russia. Acta Palaeontologica Polonica , 62(2): 290-298. https://doi.org/10.4202/app.00347.2017 Ivanov, A. O., Kovalenko, E. S., Murashev, M. M., & Podurets, K. M. (2022). Euselachian sharks (Elasmobranchii, Chondrichthyes) from the Middle and Late Permian of European Russia. Paleontological Journal , 56(11): 1372-1384. https://doi.org/10.1134/S0031030122110065 Ivanov, A. O., Nestell, M. K., Nestell, G. P., & Bell Jr, G. L. (2020). New fish assemblages from the Middle Permian from the Guadalupe Mountains, West Texas, USA. Palaeoworld , 29(2): 239-256. https://doi.org/10.1016/j.palwor.2018.10.003 Jambura, P. L., Türtscher, J., Kindlimann, R., Metscher, B., Pfaff, C., Stumpf, S., Weber, G. W., & Kriwet, J. (2020). Evolutionary trajectories of tooth histology patterns in modern sharks (Chondrichthyes, Elasmobranchii). Journal of Anatomy , 236(5): 753-771. https://doi.org/10.1111/joa.13145 Jiang, D. Y., Motani, R., Li, C., Hao, W. C., Sun, Y. L., Sun, Z. Y., & Schmitz, L. (2005). Guanling Biota: a marker of Triassic biotic recovery from the end-Permian extinction in the ancient Guizhou sea. Acta Geologica Sinica , 79(6): 729-738. https://doi.org/10.1111/j.1755-6724.2005.tb00926.x Jiang, D. Y., Zhou, M., Motani, R., Tintori, A., Fraser, N. C., Huang, J. D., Rieppel, O., Ji, C., Fu, W. L., Sun, Z. Y., & Lu, H. (2023). Emergence and ecological transition of the Mesozoic marine reptiles: evidence from the Early Triassic Chaohu and the Middle Triassic Xingyi faunas. Palaeogeography , Palaeoclimatology , Palaeoecology , 628, 111750. https://doi.org/10.1016/j.palaeo.2023.111750 Johnson, G. D. (1981). Hybodontoidei (Chondrichthyes) from the Wichita-albany Group (Early Permian) of Texas. Journal of Vertebrate Paleontology , 1(1): 1-41. Klug, S. (2010). Monophyly, phylogeny and systematic position of the Synechodontiformes (Chondrichthyes, Neoselachii). Zoologica Scripta , 39(1): 37-49. https://doi.org/10.1111/j.1463-6409.2009.00399.x Koot, M. B., Cuny, G., Orchard, M. J., Richoz, S., Hart, M. B., & Twitchett, R. J. (2015). New hybodontiform and neoselachian sharks from the Lower Triassic of Oman. Journal of Systematic Palaeontology , 13(10): 891-917. https://doi.org/10.1080/14772019.2014.963179 Lane, J. A., & Maisey, J. G. (2012). The visceral skeleton and jaw suspension in the durophagous hybodontid shark Tribodus limae from the Lower Cretaceous of Brazil. Journal of Paleontology , 86(5): 886-905. https://doi.org/10.1016/j.jsames.2014.04.002 Li, J. C., Sun, Z. Y., Cuny, G., Ji, C., Jiang, D. Y., & Zhou, M. (2022). An unusual shark assemblage from the Ladinian-Carnian interval of South China. Papers in Palaeontology , 8(1): e1404. https://doi.org/10.1002/spp2.1404 Li, Y. X., Xiao, J. F., Wei, J. Y., & Lehrmann, D. J. (2005). Ladinian-Carnian transgression and the evolution of Yangtze Carbonate Platform in southwestern Guizhou. Acta Geoscientica Sinica , 26(2): 249-253 (in Chinese with English abstract). https://doi.org/10.1111/1755-6724.2005.tb00926.x Li, Z. G., Sun, Z. Y., Jiang, D. Y., & Ji, C. (2016). LA-ICP-MS Zircon U-Pb age of the fossil layer of Triassic Xingyi Fauna from Xingyi, Guizhou, and its significance. Geological Review , 62(3): 779-790 (in Chinese with English abstract). https://doi.org/10.16509/j.georeview.2016.03.018 Lu, H., Jiang, D. Y., Motani, R., Ni, P. G., Sun, Z. Y., Tintori, A., Xiao, S. Z., Zhou, M., Ji, C., & Fu, W. L. (2018). Middle Triassic Xingyi Fauna: showing turnover of marine reptiles from coastal to oceanic environments. Palaeoworld , 27, 107-116. https://doi.org/10.1016/j.palwor.2017.05.005 Ma, L. T., Ji, C., Sun, Z. Y., Yang, P. F., & Zou, X. D. (2013). Biodiversity and stratigraphic distribution of the Triassic Xingyi marine reptile fauna, Guizhou Province. Journal of Stratigraphy , 37(2): 178-185 (in Chinese with English abstract). https://doi.org/10.19839/j.cnki.dcxzz.2013.02.006 Maisch, M. W., & Matzke, A. T. (2016). A new hybodontid shark (Chondrichthyes, Hybodontiformes) from the lower Jurassic Posidonienschiefer Formation of Dotternhausen, SW Germany. Neues Jahrbuch für Geologie und Paläontologie , Abhandlungen , 280(3): 241-257. https://doi.org/10.1127/njgpa/2016/0577 Maisey, J. G. (1983). Cranial anatomy of Hybodus basanus Egerton from the Lower Cretaceous of England. American Museum Novitates , 2758: 1-64. Malyshkina, T. P., Jagt-Yazykova, E. A., Kolchanov, V. V., & Nazarkin, M. V. (2020). First shark record from the Upper Cretaceous of the Kuril Islands, Far East Russia. Cretaceous Research , 115: 104551. https://doi.org/10.1016/j.cretres.2020.104551 Manzanares, E., Escudero-Mozo, M. J., Ferrón, H., Martínez-Pérez, C., & Botella, H. (2020). Middle Triassic sharks from the Catalan Coastal Ranges (NE Spain) and faunal colonization patterns during the westward transgression of Tethys. Palaeogeography , Palaeoclimatology , Palaeoecology , 539: 109489. https://doi.org/10.1016/j.palaeo.2019.109489 Manzanares, E., Pla, C., Ferrón, H. G., & Botella, H. (2018). Middle-Late Triassic chondrichthyans remains from the Betic Range (Spain). Journal of Iberian Geology , 44: 129-138. https://doi.org/10.1007/s41513-017-0027-1 Mollen, F. H., & Hovestadt, D. C. (2018). A new partial skeleton of a palaeospinacid shark (Neoselachii, Synechodontiformes) from the Albian of northern France, with a review of the taxonomic history of Early Cretaceous species of Synechodus Woodward, 1888. Geodiversitas , 40(4): 557-574. https://doi.org/10.5252/geodiversitas2018v40a25 Moyer, J. K., Riccio, M. L., & Bemis, W. E. (2015). Development and microstructure of tooth histotypes in the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae) and the great white shark, Carcharodon carcharias (Lamniformes: Lamnidae). Journal of Morphology , 276(7): 797-817. https://doi.org/10.1002/jmor.20380 Patterson, C. (1966). British Wealden sharks. Bulletin of the British Museum ( Natural History ), 11: 283-350. Pla, C., Márquez-Aliaga, A., & Botella, H. (2013). The chondrichthyan fauna from the Middle Triassic (Ladinian) of the Iberian Range (Spain). Journal of Vertebrate Paleontology , 33(4): 770-785. https://doi.org/10.1080/02724634.2013.748668 Saugen, S. M., Roberts, A. J., Engelschiøn, V. S., & Hurum, J. H. (2024). A new assemblage of Lower Triassic neoselachians (Chondrichthyes) from the Grippia Bonebed of Spitsbergen, Norway. Journal of Vertebrate Paleontology , 44(3), e2426544. https://doi.org/10.1080/02724634.2024.2426544 Schnetz, L., Pfaff, C., & Kriwet, J. (2016). Tooth development and histology patterns in lamniform sharks (Elasmobranchii, Lamniformes) revisited. Journal of Morphology , 277(12): 1584-1598. https://doi.org/10.1002/jmor.20597 Seilacher, A. (1943). Elasmobranchier-Reste aus dem oberen Muschelkalk und dem Keuper Württembergs. Neues Jahrbuch für Mineralogie , Geologie und Paläontologie , Monatshefte B , 1943: 256-292. Stumpf, S., López‐Romero, F. A., Kindlimann, R., Lacombat, F., Pohl, B., & Kriwet, J. (2021). A unique hybodontiform skeleton provides novel insights into Mesozoic chondrichthyan life. Papers in Palaeontology , 7(3): 1479-1505. https://doi.org/10.1002/spp2.1350 Thies, D., Vespermann, J., & Solcher, J. (2014). Two new neoselachian sharks (Elasmobranchii, Neoselachii, Synechodontiformes) from the Rhaetian (Late Triassic) of Europe. Palaeontographica , Abteilung A , 303(4-6): 137-167. https://doi.org/10.1127/pala/303/2014/137 Tintori, A., Sun, Z. Y., Ni, P. G., Lombardo, C., Jiang, D. Y., & Motani, R. (2015). Oldest stem Teleostei from the late Ladinian (Middle Triassic) of southern China. Rivista Italiana di Paleontologia e Stratigrafia , 121(3): 285-296. https://doi.org/10.13130/2039-4942/6519 Underwood, C. J., Mitchell, S. F., & Veltkamp, C. J. (1999). Microborings in mid-Cretaceous fish teeth. Proceedings of the Yorkshire Geological Society , 52(3): 269-274. https://doi.org/10.1144/pygs.52.3.269 Underwood, C. J., & Ward, D. J. (2004). Neoselachian sharks and rays from the British Bathonian (Middle Jurassic). Palaeontology , 47(3): 447-501. https://doi.org/10.1111/j.0031-0239.2004.00386.x Underwood, C. J., & Ward, D. J. (2008). Sharks of the Order Carcharhiniformes from the British Coniacian, Santonian and Campanian (Upper Cretaceous). Palaeontology , 51(3): 509-536. https://doi.org/10.1111/j.1475-4983.2008.00757.x Wang, X. F., Bachmann, G., Hans, H., Sander, P., Cuny, G., Chen, X. H., Wang, C. S., Chen, L. D., Cheng, L., Meng, F. S., & Xu, G. H. (2008). The Late Triassic black shales of the Guanling area, Guizhou Province, South-west China: a unique marine reptile andpelagic crinoid fossil lagerstatte. Palaeontology , 51 (1), 27-61. https://doi.org/10.1111/j.1475-4983.2007.00735.x Yin, H. F. (1982). Discussion on the Ladinian stage in China. Geological Review , 28(3): 235-239 (in Chinese with English abstract). Zhang, B. M., Chen, X. H., Cheng, L., & Zhang, M. (2012). Middle Triassic (Ladinian) elasmobranch scales from the southwestern Guizhou, China. Acta Micropalaeontologica Sinica , 29(1): 52-61 (in Chinese with English abstract). https://doi.org/10.1007/s11783-011-0280-z Zhang, Z. T., & Sun, Y. D. (2023). The Ladinian-Carnian conodont fauna at Yize, Yunnan, southwestern China, with implications for conodont palaeoecology and palaeogeography. Geological Magazine , 160(4): 776-793. https://doi.org/10.1017/S0016756822001236 Zou, X. D., Balini, M., Jiang, D. Y., Tintori, A., Sun, Z. Y., & Sun, Y. L. (2015a). Ammonoids from the Zhuganpo Member of the Falang Formation at Nimaigu and their relevance for dating the Xingyi fossil-lagerstätte (late Ladinian, Guizhou, China). Rivista Italiana di Paleontologia e Stratigrafia , 121(2): 135-161. https://doi.org/10.13130/2039-4942/6511 Zou, X. D., Guo, W., Jiang, D. Y., & Sun, Z. Y. (2015b). Preliminary analysis of environment of fossils reservoir of Xingyi Fauna in Guizhou Province. Acta Scientiarum Naturalium Universitatis Pekinensis , 51(3): 472-484 (in Chinese with English abstract). https://doi.org/10.13209/j.0479-8023.2014.179 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7193674","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":490271320,"identity":"333cb1c7-2f2f-4004-82de-f76cfe1a3b37","order_by":0,"name":"Siyan Zhao","email":"","orcid":"","institution":"Peking University","correspondingAuthor":false,"prefix":"","firstName":"Siyan","middleName":"","lastName":"Zhao","suffix":""},{"id":490271321,"identity":"1c120dce-7540-4aed-b9e1-47fd0a8c0187","order_by":1,"name":"Jiachun Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYBACPmaGhAMMDEDE3gAVOkBACxtcCw9MKUEtcGUSCcRqYWd4eOBHzZ3E7ZJvjD/ztjHI8d1IYPxcQMBhB3uOPUvcOTstTRqoxVjyRgKz9AwCWg7wNhxO3HA7+RgzUEvihhsJbMw8hGz5C9Jy82AzyGH1RGk5DLblBvMBkMMSDIjSInPssPGGM2lpknPOSRjOPPOwWRqfFn7+M8kf39Qclt1w/IzxhzdlNvJ8x5MPfsanBRiFCXAmEw+DBJBibMCrAZhQDsCZjD8IqB0Fo2AUjIKRCQANDFBe+NhrhAAAAABJRU5ErkJggg==","orcid":"","institution":"Xi’an Shiyou University","correspondingAuthor":true,"prefix":"","firstName":"Jiachun","middleName":"","lastName":"Li","suffix":""},{"id":490271322,"identity":"def40179-2e95-4b26-a12b-d08b802561b5","order_by":2,"name":"Gilles Cuny","email":"","orcid":"","institution":"Université Claude Bernard Lyon 1, LEHNA UMR 5023, CNRS, ENTPE","correspondingAuthor":false,"prefix":"","firstName":"Gilles","middleName":"","lastName":"Cuny","suffix":""},{"id":490271323,"identity":"d0789754-edde-4d80-bf45-968ac52babe3","order_by":3,"name":"Zuoyu Sun","email":"","orcid":"","institution":"Peking University","correspondingAuthor":false,"prefix":"","firstName":"Zuoyu","middleName":"","lastName":"Sun","suffix":""}],"badges":[],"createdAt":"2025-07-23 08:08:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7193674/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7193674/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87825009,"identity":"c30a201d-99ec-451e-b128-2cc6b8e9d8ea","added_by":"auto","created_at":"2025-07-29 11:39:56","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":129616,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA.\u003c/strong\u003e geographic location of the Nimaigu and Yize sections. \u003cstrong\u003eB\u003c/strong\u003e. stratigraphic column of the Nimaigu section showing the distribution of chondrichthyan fossils (modified from Zou et al., 2015a and Li et al., 2022).\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/80f09ca759fb214eb2d2c92a.jpg"},{"id":87825007,"identity":"d12df1fa-849e-40b9-8f1c-fb20a8adb2b3","added_by":"auto","created_at":"2025-07-29 11:39:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":76354,"visible":true,"origin":"","legend":"\u003cp\u003eSEM pictures of Euselachii gen. et sp. indet.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA-E\u003c/strong\u003e. anterolateral tooth, GMPKU-P-4261. \u003cstrong\u003eF-J\u003c/strong\u003e. anterolateral tooth, GMPKU-P-4262. \u003cstrong\u003eK-O\u003c/strong\u003e. anterolateral or posterolateral tooth, GMPKU-P-4263. \u003cstrong\u003eP-T\u003c/strong\u003e. posterolateral tooth, GMPKU-P-4264. \u003cstrong\u003eU-Y\u003c/strong\u003e. posterolateral tooth, GMPKU-P-4265. Images in the same column from left to right represent the labial, lingual, apical, basal and lateral views. All scale bars equal 200 μm.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/44826ddf4bc58e3bcae710f6.jpg"},{"id":87827335,"identity":"b3fd13d0-ee27-415e-82eb-a74dad56a939","added_by":"auto","created_at":"2025-07-29 11:55:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":122804,"visible":true,"origin":"","legend":"\u003cp\u003eVirtual reconstruction of GMPKU-P-4263\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA-E\u003c/strong\u003e. surface rendering: A, lingual view; B, apical view; C, basal view; D, mesial view; E labial view; lines a, b and c indicate the orientations of sections G, F, and H, respectively. \u003cstrong\u003eF-H\u003c/strong\u003e. virtual sections. F, sagittal view; H, frontal view; G, cross-section of the distal crown. \u003cstrong\u003eI-V\u003c/strong\u003e. reconstruction of vascular canals: I and M, labial view; J and N, lingual view; K and O, mesial view; L and P, distal view; Q and T, apical view; R and U, basal view; S and V, magnification of the distal part of lvc in apical view. All scale bars equal 200 μm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAbbreviations\u003c/strong\u003e: en, enameloid; or, orthodentine; os, osteodentine; avc, ascending vascular canal; cvc, connective vascular canal; lvc, longitudinal vascular canal; vp, vascular plexus.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/db519f0159daf1d38f87cc4c.jpg"},{"id":87827336,"identity":"42c49131-abd2-4500-99ca-05cb4d2fbfea","added_by":"auto","created_at":"2025-07-29 11:55:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":138990,"visible":true,"origin":"","legend":"\u003cp\u003eSEM pictures and virtual reconstruction of GMPKU-P-4266 (Neoselachii gen. et sp. indet. 1)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA-E\u003c/strong\u003e. SEM pictures. Images from left to right represent the labial, lingual, apical, basal and distal views.\u003cstrong\u003e F-J\u003c/strong\u003e. surface rendering: F, labial view; G, apical view; H, basal view; I, distal view; J, lingual view; lines a, b and c indicate the orientations of sections L, K, and M, respectively. \u003cstrong\u003eK-M\u003c/strong\u003e. virtual sections. K, sagittal view; L, axial view; M, frontal view. \u003cstrong\u003eN-W\u003c/strong\u003e. reconstruction of vascular canals (red): N and Q, lingual view; O and R, linguo-apical view; P and S, labial view; T and V, apical view; U and W, basal view. \u003cstrong\u003eX and Y\u003c/strong\u003e, reconstruction of vascular canals (red) and irregular canals (green): X, lingual view; Y, basal view. All scale bars equal 200 μm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAbbreviations\u003c/strong\u003e: en, enameloid; or, orthodentine; pc, pulp cavity; os, osteodentine; avc, ascending vascular canal; lvc, longitudinal vascular canal; cvc, connective vascular canals; mtvc, main transverse vascular canal; stvc, secondary transverse vascular canal; op, openings of irregular canals.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/400ea33318c97a6ea0baae44.jpg"},{"id":87825729,"identity":"139cbf2b-eb0a-474c-9a31-1721e132ea22","added_by":"auto","created_at":"2025-07-29 11:47:56","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":23896,"visible":true,"origin":"","legend":"\u003cp\u003eSEM pictures of GMPKU-P-4267, Neoselachii gen. et sp. indet. 2\u003c/p\u003e\n\u003cp\u003eImages from left to right represent the labial, lingual, apical, basal and lateral views. All scales bars equal 200 μm.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/cb373eab8eafb595f93703bc.jpg"},{"id":87825730,"identity":"bfb9259d-e22a-4234-871c-555bd8d98b63","added_by":"auto","created_at":"2025-07-29 11:47:56","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":38018,"visible":true,"origin":"","legend":"\u003cp\u003eSEM pictures of Hexanchidae? gen. et sp. indet.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA-E\u003c/strong\u003e. ? anterolateral tooth, GMPKU-P-4268. \u003cstrong\u003eF-J\u003c/strong\u003e. ? anterolateral tooth, GMPKU-P-4269. Images in the same column from left to right represent the labial, lingual, apical, basal and lateral views. All scales bars equal 200 μm.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/b6e178a6893d30d301c7afae.jpg"},{"id":99314412,"identity":"396b9c6a-338e-45b6-a9a8-caddfd91d47b","added_by":"auto","created_at":"2025-12-31 16:21:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1529447,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7193674/v1/e1d82851-5a0e-4644-90e3-9fa19f70b61f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"New euselachian teeth from the Ladinian-Carnian interval of Guizhou and Yunnan Provinces, South China","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe Ladinian-Carnian \u0026lsquo;Falang\u0026rsquo; Formation in southwestern Guizhou and eastern Yunnan Provinces consists of the Zhuganpo Member and Wayao Member in ascending stratigraphic order. It is renowned for yielding two marine vertebrate Lagerst\u0026auml;tten that recorded exceptionally well-preserved marine reptiles and fishes, viz. the latest Ladinian Xingyi Fauna and the early Carnian Guanling Biota, respectively (Jiang et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2005\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Benton et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tintori et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lu et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Fang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although scarce in the fossil record, chondrichthyan remains from the Zhuganpo Member of Guizhou Province were documented in previous studies (Chen, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Chen and Cuny, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). To date, nine tooth taxa have been identified in Guizhou Province. These include three hybodonts (\u003cem\u003eOmanoselache\u003c/em\u003e (\u0026lsquo;\u003cem\u003ePolyacrodus\u003c/em\u003e\u0026rsquo;) \u003cem\u003econtrarius\u003c/em\u003e, ?\u003cem\u003eParvodus\u003c/em\u003e and ?Hybodontiformes) and one potential neoselachian (Neoselachii?) from Guanling County (Chen and Cuny, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Additionally, a shark assemblage from Xingyi City (Nimaigu section) comprises two elasmobranchs with uncertain affinity (aff. \u003cem\u003eRosaodus\u003c/em\u003e sp. and \u003cem\u003eRosaodus xingyiensis\u003c/em\u003e), two indeterminate euselachians (Euselachii gen. et sp. indet. and \u003cem\u003eFavusodus orientalis\u003c/em\u003e), and one synechodontiform shark (\u003cem\u003eKeichouodus nimaiguensis\u003c/em\u003e) (Li et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This fauna is dominated by sharks with a cladodont-like dentition and almost devoid of durophagous euselachians, which makes it different from all other contemporaneous shark faunas worldwide. Herein, we present nine newly founded euselachian teeth from the Zhuganpo Member of the \u0026lsquo;Falang\u0026rsquo; Formation at the Nimaigu and Yize sections in South China. Both external tooth morphologies and internal dental vascular system have been described in detail. The study not only enhances our understanding of the diversity of the chondrichthyan assemblage from the \u0026lsquo;Falang\u0026rsquo; Formation in South China, but also, for the first time, reveals the three-dimensional dental microstructure of Triassic chondrichthyan teeth.\u003c/p\u003e\u003cp\u003e\u003cb\u003eGeological setting\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe teeth described in the present study have been found in two sites, i.e. the Nimaigu section (25\u0026deg;09\u0026prime;52\u0026Prime;N, 104\u0026deg;47\u0026prime;19\u0026Prime;E) in Wusha Town, Xingyi City, southwestern Guizhou Province, and the Yize section (25\u0026deg;01'06.8\"N, 104\u0026deg;27'56.1\"E) in Changdi Town, Luoping County, Qujing City, eastern Yunnan Province, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). During the Triassic, these two sampled sites were located on the southwestern part of the Yangtze Carbonate Platform. Because of the collision between the Yangtze and North China plates during the Ladinian, a large-scale regression occurred across much of the Yangtze (Yin, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). However, the studied area experienced a transgression caused by tectonic differentiation, as indicated by the stratigraphic succession that records an upward transition from shallow-water dolomite of the Yangliujing Formation to deep-water marl and nodular limestone of the Zhuganpo Member, and subsequently to the black shale and marl of the Wayao Member that represents the maximum flooding surface (Enos et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). At the Nimaigu section, a continuous stratigraphic succession spanning from the uppermost Yangliujing Formation to the basal part of the Wayao Member of the \u0026lsquo;Falang\u0026rsquo; Formation is well-exposed through research excavations (Lu et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Therein, the Ladinian-Carnian interval is constrained by the early Carnian \u003cem\u003eTrachyceras\u003c/em\u003e ammonoid beds, which occur between layers 197 and 238, and by an LA-ICP-MS U-Pb zircon age of 239.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7 Ma of the layer 161 (Zou et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The lithology and stratigraphy of the Nimaigu section are described in detail by Ma et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), Zou et al. (\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e/b), Li et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), Lu et al. (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Chai et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The Yize section is a newly excavated Ladinian-Carnian section that is laterally correlated to the Niamigu section. It consists of the Zhuganpo Member and the overlying Wayao Member, and five conodont zones have been established therein, viz. in ascending order: the \u003cem\u003eParagondolella inclinata\u003c/em\u003e Zone, the \u003cem\u003eQuadralella polygnathiformis\u003c/em\u003e Zone, the \u003cem\u003eQuadralella praelindae\u003c/em\u003e Zone, the \u003cem\u003eQuadralella auriformis\u003c/em\u003e Zone and the \u003cem\u003eQuadralella robusta\u003c/em\u003e Zone. The Ladinian-Carnian interval is constrained by the first occurrences of the conodonts \u003cem\u003eQuadralella polygnathiformis\u003c/em\u003e and \u003cem\u003eQuadralella intermedia\u003c/em\u003e within the Zhuganpo Member (Zhang and Sun, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eDuring the fieldwork in 2017, 2018 and 2019, we collected large amounts of rock samples from the \u0026lsquo;Falang\u0026rsquo; Formation at the Nimaigu and Yize sections. These samples were broken into fragments approximately 4 cm in size and subsequently dissolved using 10% acetic acid. Conodont and chondrichthyan fossils were then manually picked from the residues under a stereomicroscope. This study examined a total of nine shark teeth: GMPKU-P-4268 from the Yize section, and GMPKU-P-4261-4267, 4269 from the Nimaigu section. They were photographed using a JEOL JCM-6000 Plus scanning electron microscope (SEM) under an acceleration voltage of 10 kV at the School of Earth and Space Sciences, Peking University. The specimens GMPKU-P-4263 and GMPKU-P-4266 were scanned using a SkyScan 1172 micro-CT device at the State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences. Micro-CT scanning was performed with a 180\u0026deg; rotation, a rotation step of 0.2\u0026deg; and a pixel size of 0.56 \u0026micro;m. The source voltage and current were set to 48 kV and 200 mA, respectively. The teeth and their vascular system were three-dimentionally reconstructed using Avizo 2022.2. All specimens are housed in the Geological Museum of Peking University (GMPKU), Beijing, China.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSystematic palaeontology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe systematic framework and tooth morphological terminology follow Ginter et al. (\u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e), Thies et al. (\u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e) and Cappetta (\u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e). Dental histological terminology follows Jambura et al. (\u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e). The vascular terminology follows Ivanov (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), and Ivanov and Duffin (\u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClass Chondrichthyes\u003c/strong\u003e Huxley, \u003cspan class=\"CitationRef\"\u003e1880\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSubclass Elasmobranchii\u003c/strong\u003e Bonaparte, \u003cspan class=\"CitationRef\"\u003e1838\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCohort Euselachii\u003c/strong\u003e Hay, \u003cspan class=\"CitationRef\"\u003e1902\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEuselachii gen. et sp. indet.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReferred specimens\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFive isolated teeth, GMPKU-P-4261-4265.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLocality and horizon\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layers 79, 84, 146, 152\u0026ndash;153 and 186, Zhuganpo Member, Falang Formation (late Ladinian, Middle Triassic).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDescription of morphological characteristics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe teeth are elongated mesiodistally and narrow labiolingually. All teeth are broken, measuring 0.21\u0026ndash;0.37 mm in height, 0.15\u0026ndash;0.28 mm labio-lingually and 0.58\u0026ndash;1.10 mm mesio-distally. A gradient monognathic heterodonty is characterized by anterolateral teeth with arched root and relatively separated cusps, whereas posterolateral teeth display a straight root and fused cusps.\u003c/p\u003e\n\u003cp\u003eThe crown possesses a main cusp flanked by 2 to 4 lateral cusplets on each side, without any intermediate cusplets. The main cusp is robust and pyramidal (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eR). The lateral cusplets decrease in height laterally (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eU), with the highest being always lower than the main cusp. One or two intermediate cusplets are usually present between the main cusp and the first pair of lateral cusplets (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eF, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eP). These intermediate cusplets are significantly smaller than lateral ones. The mesial and distal extremities of the crown sometimes display a small protuberance or accessory cusplet, which protrudes obliquely from the outermost lateral cusplet (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eP, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eU). All cusps are inclined distally and curved lingually (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eP, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eO). The adjacent cusps are well-separated by V-shaped notches on the anterolateral teeth (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA), whereas they are fused at their base on the posterolateral teeth (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eU). In apical view, each cusp presents an acute apex where the mesial and distal cutting edges converge (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eU).\u003c/p\u003e\n\u003cp\u003eThe main cusp and some lateral cusplets exhibit a prominent triangular protrusion on the labial and/or lingual side, whose apex is connected to that of the corresponding cusp by a ridge (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eF, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eE). There are 1 to 2 vertical ridges on the upper part of the cusp when no triangular protrusion is present (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eK, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eP). The crown of GMPKU-P-4263 displays eight mesiodistally compressed humps, which either connect with an overlying ridge (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eK, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eL) or lie on the lower part of the triangular protrusion (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eD, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eE). The crown-root junction displays a distinct incision lingually, but it is not well marked labially (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eE).\u003c/p\u003e\n\u003cp\u003eThe root of GMPKU-P-4263 is relatively well preserved. It is low and rectangular (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eN), protruding labially and lingually, although the labial protrusion is significantly less developed. There is a row of small foramina on the labial root face (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eK). Foramina on the lingual face of the root are more randomly distributed than those on the labial one. The basal face of the root is flat and presents several small to large foramina, which are restricted to the labial part (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eC). The vascularization is anaulacorhize.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDescription of internal structure\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe crown consists of enameloid and a compact layer of underlying orthodentine (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eF). The orthodentine enfolds a large longitudinal vascular canal (pulp cavity?) at the crown-root junction. However, no ascending pulp cavity can be seen (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eF, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eH). Osteodentine is restricted to the root (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eH). Therefore, the histotype is orthodont. The vascular system consists of a longitudinal vascular canal, a vascular canal plexus, connective vascular canals and ascending vascular canals. The longitudinal vascular canal is cylindrical, with a diameter ranging from 30 to 90 \u0026micro;m. It extends along the crown-root junction and almost reaches the mesial and distal extremities of the root (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eI). At the distal extremity, the longitudinal canal branches into three thinner canals (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eV). The single-layered vascular plexus consists of interconnected canals ranging from 8 to 40 \u0026micro;m in diameter, forming numerous circular grids (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eU). The vascular plexus extends both labially and lingually, terminating as foramina on the corresponding root faces (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eO, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eP, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eT). The meshed vascular plexus connects to the overlying longitudinal vascular canal through short connective vascular canals (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eN, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eO) and connects to the underlying ascending vascular canals (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eR, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eU).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRemarks\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe material is reminiscent of an indeterminate euselachian from the late Ladinian (Middle Triassic) of the same locality (Li et al, \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). They share a similar pattern of monognathic heterodonty, cladodont-like crown, pyramidal main cusp, labially and lingually protruding root and anaulacorhize vascularization. However, the teeth described herein differ from Euselachii gen. et sp. indet. in Li et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e by having significantly more developed labial and lingual triangular protrusions on the main cusp and lateral cusplets. Additionally, a presumed posterior tooth of ?Hybodontidae from the early Carnian of Guanling, Guizhou, also shows a labial triangular protrusion on the main cusp, intermediate cusplets between main cusp and lateral cusplets, well-defined cusps, incised crown-root junction and arched root with both labial and lingual foramina (Chen and Cuny, \u003cspan class=\"CitationRef\"\u003e2003\u003c/span\u003e). The presence of intermediate cusplets in our materials, as well as in the tooth from Guanling, do not fit the typical crown morphology of Hybodontiformes, which normally displays a gradually decreasing height of the cusps (Ginter et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Koot et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e). We tentatively assign our material to a taxon that is closely allied, if not identical, to the Euselachii gen. et sp. indet. of Li et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) and ?Hybodontidae indet. of Chen and Cuny (\u003cspan class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSubcohort Neoselachii Compagno, 1977\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOrder incertae sedis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNeoselachii gen. et sp. indet.\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigures 4\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eReferred specimens\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOne broken tooth, GMPKU-P-4266\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLocality and horizon\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layers 145-146, Zhuganpo Member, \u0026lsquo;Falang\u0026rsquo; Formation (late Ladinian, Middle Triassic).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription of morphological characteristics\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe tooth measures 0.75 mm in height, 0.53 mm labio-lingually and 1.43 mm mesio-distally. The crown displays a robust main cusp flanked by one lateral cusplet on the mesial side and two lateral cusplets on the distal side. The main cusp is biconvex, curved lingually and slightly inclined distally\u003cs\u003e\u0026nbsp;\u003c/s\u003e(Figure 4A, 4E). Its cutting edges are well developed and connected to adjacent lateral cusplets (Figure 4C). The lateral cusplets are broken.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe labial face of the main cusp is devoid of ornamentation (Figure 4A). Lingually, there are 7\u0026nbsp;faint vertical ridges with varying lengths (Figure 4B). The crown-root junction shows a slight incision labially, but it is not well marked on the lingual side (Figure 4F, 4G).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe root is low (no more than 30% of the height of the tooth), and kidney-shaped in basal view (Figure 4G, 4H). It protrudes lingually and swells at the middle part of the root (Figure 4I, 4J). The root is slightly arched on the labial side but remains straight on the lingual side (Figure 4F, 4G). The distal and mesial extremities of the labial face of the root displays 3 and 4 foramina, respectively (Figure 4F). Lingually, the root exhibits two rows of foramina. The upper row has 8 small to moderate foramina that are located near the crown-root junction, whereas the lower row consists of 4 larger foramina, situated in the central part of the lingual face of the root (Figure 4G, 4J). The basal face of the root shows numerous\u0026nbsp;randomly distributed foramina with varying sizes. A mesio-distal depression is present on the labial part of the basal face of the root, which contains a row of foramina accompanied by very short unroofed canals (Figure 4H). The vascularization may represent a transitional state between anaulacorhize and polyhemiaulacorhize.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription of internal structure\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe crown is composed of an outer enameloid and inner orthodentine layer, which encases a reduced pulp cavity ascending within the main cusp (Figure 4K).\u0026nbsp;The orthodentine is compact with a high density (Figure 4K, 4M). Some deposits of medium to low density are distributed in the central area of the main cusp and within the cavities (Figure 4K, 4L, 4M). Osteodentine is confined to the root and does not invade the pulp cavity (Figure 4K, 4M). Therefore, the tooth histotype is orthodont. The vascular system contains two longitudinal vascular canals, connective vascular canals, a pulp cavity, main transverse vascular canals, secondary transverse vascular canals and ascending vascular canals. The two longitudinal vascular canals are 130 to 150 \u0026mu;m in diameter and nearly the same mesio-distal length as the tooth (Figure 4N, 4O). The upper and lower longitudinal vascular canals are interconnected by several short vertical or oblique connective vascular canals (Figure 4R, 4S). The upper longitudinal vascular canal is interconnected with a small pulp cavity above (Figure 4Q). There are four parallel main transverse vascular canals in the middle of the root, with diameters ranging from 52 to 93 \u0026mu;m. The main transverse vascular canals run labiolingually from the lingual face of the root and terminate in the basal depression (Figure 4O, 4U, 4V). They connect to the overlying longitudinal vascular canals through a few short connective canals (Figure 4W). The secondary transverse vascular canals are shorter and narrower than the main transverse vascular canals (Figure 4V, 4W). The main and secondary transverse vascular canals are sometimes interconnected by short connective vascular canals (Figure 4U). A main transverse vascular canal and two secondary vascular canals extend labially from the middle part of the lower longitudinal vascular canal and are interconnected at their extremities by two longitudinal connective vascular canals, without opening externally. The ascending vascular canals are short and interconnected with transverse vascular canals. They open on both apical and basal faces of the root (Figure 4O, 4U). In addition to the vascular canals, there are long, narrow and randomly extended irregular canals, likely a result of microbial activity (Underwood et al., 1999; Cappetta, 2012). They are primarily distributed around the pulp cavity (Figure 4X) and may open on the root surface (Figure 4X, 4Y).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eRemarks\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGMPKU-P-4266 resembles \u003cem\u003eRosaodus\u003c/em\u003e, a cladodont-like shark from the late Ladinian of the Nimaigu section (Li et al., 2022), with a conical and lingually curved main cusp, a labially depressed basal root and a swollen lingual root. However, it differs from \u003cem\u003eRosaodus\u003c/em\u003e by possessing radially arranged ridges on the lingual face of the main cusp, large foramina in the depression of the basal face of the root and double rows of foramina on the lingual face of the root. Additionally, the well-defined high main cusp and lingually displaced root with a basal labial depression where some foramina open, are reminiscent of two Anisian Neoselachii: \u003cem\u003eMucrovenator\u0026nbsp;\u003c/em\u003eand\u003cem\u003e\u0026nbsp;Rhomaleodus\u003c/em\u003e (Cuny et al., 2001; Andreev and Cuny, 2012). However, GMPKU-P-4266 exhibits an unornamented labial crown face and two rows of foramina on the lingual root face, whereas the labial crown face of \u003cem\u003eMucrovenator\u0026nbsp;\u003c/em\u003eand \u003cem\u003eRhomaleodus\u003c/em\u003e are both ornamented with vertical ridges, and the lingual face of the root displays only a single row of foramina. Besides, the imperforate labial root face and flat crown-root junction of \u003cem\u003eMucrovenator\u003c/em\u003e, and the bifurcated ridges and constricted crown-root transition of \u003cem\u003eRhomaleodus\u003c/em\u003e also differ from those of GMPKU-P-4266. These differences therefore preclude assigning GMPKU-P-4266 to \u003cem\u003eMucrovenator\u0026nbsp;\u003c/em\u003eor to\u003cem\u003e\u0026nbsp;Rhomaleodus\u003c/em\u003e. Nevertheless, its vascularization displaying large foramina openings in the mesiodistal depression on the basal face of the root points to an affinity with Neoselachii.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNeoselachii gen. et sp. indet.\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 5\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eReferred specimens\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOne anterior tooth, GMPKU-P-4267\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLocality and horizon\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNimaigu village, Wusha Town, Xingyi City, Guizhou Province, China. Layer 186, Zhuganpo Member, \u0026lsquo;Falang\u0026rsquo; Formation (late Ladinian, Middle Triassic).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription of morphological characteristics\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe tooth measures 0.56 mm mesiodistally, 0.37 mm labiolingually and 0.68 mm in height. The crown bears a slender main cusp without lateral cusplet. The main cusp displays two sharp cutting edges laterally (Figure 5E) and a keel-like protrusion on the lower part of its lingual face. It is strongly biconvex, curved lingually and slightly inclined distally (Figure 5B, 5E). The crown has no ornamentation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe root is low and consists of two symmetrical lobes. The lobes are triangular, flattened and elongated mesiodistally in apical and basal views (Figure 5C, 5D). They lean downward at an angle of approximately 45\u0026deg;, giving the root an inverted V-shaped outline in labial and lingual views (Figure 5A, 5B). The central part of the lingual face of the root is swollen and partly separated by a nutritive canal forming a large foramen (Figure 5C). The basal root face is flat and shows an unroofed median canal on the lingual part (Figure 5D). The root vascularization reminds therefore of a hemiaulacorhize type.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eRemarks\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGMPKU-P-4267 reminds of an undetermined neoselachian shark from the Ladinian-Carnian interval of Guanling, Guizhou Province (Chen et al., 2007). They share a slender and lingually curved main cusp, unornamented crown, V-shaped and triangular root with a lingually unroofed median canal. However, the tooth from Guanling exhibits a pair of lateral cusplets on the crown, several foramina on the lingual face of the root lobes and a labially incised crown-root junction (Chen et al., 2007: Figs. 4A, 4D). These differences may be explained by some heterodonty pattern (monognathic, dignathic, gynandric or ontogenetic), but with only two teeth recovered so far, no pattern can be demonstrated. Besides, the tooth from Guanling displays a less roofed median canal on the basal face of the root (Chen et al., 2007: Fig. 4C), perhaps resulting from intraspecific variation. However, the tooth from Guanling (6 mm mesiodistally) is significantly larger than the tooth from Xingyi (0.56 mm mesiodistally), yet the size data for the former do not correspond to the scales shown in the plate (Chen et al., 2007: Figs. 4A-4D). Therefore, the specimens from Xingyi and Guanling could belong to the same species. At the minimum, they are closely related. In accordance with Chen et al. (2007), we assign GMPKU-P-4267 to the Neoselachii based on its hemiaulacorhize-like vascularization.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Based on the presence of a well-developed median lingual protuberance and median vascular canal, Chen et al. (2007) proposedthat the Guanling specimen might be closely related to the Palaeozoic Neoselachii \u003cem\u003eCooleyella\u003c/em\u003e, which has been recovered from the Mississippian to the Guadalupian (Ivanov and Duffin, 2024). However, \u003cem\u003eCooleyella\u003c/em\u003e displays one or two foramina on the basal face of the root (Duffin and Ward, 1983; Duffin et al., 1996; Ivanov and Duffin, 2024), which is not the case in the Chinese specimens from Xingyi and Guanling. The slender, conical main cusp, bilobate root with a flat basal face showing a partially roofed median canal, and a central foramen on the lingual root of the Chinese material, are reminiscent of the teeth of certain Scyliorhinidae, such as \u003cem\u003eApristurus laurussonii\u003c/em\u003e and \u003cem\u003ePseudoscyliorhinus reussi\u003c/em\u003e (Herman et al., 1990; Underwood and Ward, 2008; Cappetta, 2012). However, the root lobes of the Chinese specimens are extending downward and labially aligned, whereas those of Scyliorhinidae are coplanar and labially displaced. In addition, the unornamented crown, non-porous labial root lobes and the absence of labial root protrusion also preclude the attribution of GMPKU-P-4267 to the Scyliorhinidae.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSuperorder Squalomorphii? Compagno, 1973\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOrder Hexanchiformes? de Buen, 1926\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFamily Hexanchidae? Gray 1851\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHexanchidae? gen. et sp. indet.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 6\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eReferred specimens\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTwo isolated teeth, GMPKU-P-4268 and 4269.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLocality and horizon\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNimaigu village, Wusha Town, Xingyi City, Guizhou Province, China; Layers 145-146, Zhuganpo Member, \u0026lsquo;Falang\u0026rsquo; Formation (late Ladinian, Middle Triassic). Changdi Township, Luoping County, Qujing City, Yunnan Province; Zhuganpo Member, \u0026lsquo;Falang\u0026rsquo; Formation (early Carnian, Late Triassic).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eof morphological characteristics\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe broken teeth measure 1.18-1.33 mm mesiodistally, 0.22-0.25 mm labiolingually and 0.68-1.47 mm in height. The crown is compressed\u0026nbsp;labiolingually (Figure 6J). It bears a triangular main cusp flanked by three pairs of smaller lateral cusplets. The lateral cusplets on each side of the main cusp decrease in height laterally, and the outmost pair of cusplets is much reduced (Figure 6F). All cusps are distally inclined and separated by V-shaped notches. The cutting edges of the cusps are well developed and interconnected. No ornamentation is present on the crown. The base of the crown,\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eor the possible uppermost part of the root, protrudes slightly toward the lingual side (Figure 6I, 6J).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eRemarks\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGMPKU-P-4268 and 4269 resemble teeth of Hexanchidae because of their labiolingually compressed crown, distally inclined triangular cusps comprising a main cusp flanked by smaller lateral cusplets whose height decreases laterally (Cappetta, 2012; Cappetta and Grant-Mackie, 2018). These teeth are also comparable to Hexanchidae gen. et sp. indet. from the late Permian of Japan and ?\u003cem\u003eparanotidanus\u003c/em\u003e sp. from the middle Jurassic of England (Underwood and Ward, 2004; Burrow et al., 2008). However, the root is missing in our material, which makes it difficult to ascribe it to Hexanchidae with certainty, and more complete specimens are needed to determine their affiliation. Here, we tentatively assign them to Hexanchidae considering their\u0026nbsp; crown morphology.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eBiostratigraphy and Palaeoecology\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStratigraphically, one tooth of Hexanchidae? gen. et sp. indet. (GMPKU-P-4269) is recovered from layers 145-146 of the Zhuganpo Member of the ‘Fanglang’ Formation at the Nimaigu section (late Ladinian, Zou et al., 2015a). The age of layers 145-146 were considered to be the late Ladinian that below the early Carnian \u003cem\u003eTrachyceras\u003c/em\u003e beds (Zou et al., 2015a) (Figure 1B). Another tooth of Hexanchidae? gen. et sp. indet. (GMPKU-P-4268) is collected from the Zhuganpo Member of the ‘Fanglang’ Formation at the Yize section, present above the first occurrences of conodonts \u003cem\u003eQuadralella polygnathiformis\u003c/em\u003e and \u003cem\u003eQuadralella intermedia\u003c/em\u003e at this section (early Carnian, Zhang and Sun, 2023). Nevertheless, their biostratigraphic frameworks were established using different fossil groups (ammonoid zones in the Nimaigu section versus conodont zones in the Yize section). Whether these two sections are completely synchronous requires further verification through detailed stratigraphic measurements and microfacies analysis. The remaining three taxa are distributed between layers 79 and 186 exclusively at the Nimaigu section, occurring from the late Ladinian \u003cem\u003eHaoceras xingyiense\u003c/em\u003e Zone but not extending into the early Carnian \u003cem\u003eTrachyceras\u003c/em\u003e beds (Zou et al., 2015a) (Figure 1B). Therefore, Hexanchidae? gen. et sp. indet. is the only taxon may across the Ladinian-Carnian boundary, whereas the remaining three taxa are confined to the late Ladinian. Six chondrichthyan taxa previously described from the Nimaigu section include Elasmobranchii incertae sedis (aff. \u003cem\u003eRosaodus\u003c/em\u003e sp., \u003cem\u003eRosaodus\u003c/em\u003e \u003cem\u003exingyiensis\u003c/em\u003e), Euselachii (Euselachii gen. et sp. indet., \u003cem\u003eFavusodus\u003c/em\u003e \u003cem\u003eorientalis\u003c/em\u003e, \u003cem\u003eKeichouodus\u003c/em\u003e \u003cem\u003enimaiguensis\u003c/em\u003e), and a possible Holocephali (aff. \u003cem\u003eArctacanthus\u003c/em\u003e sp.) (Li et al., 2022). The chondrichthyan teeth described in this study add three new euselachians: Neoselachii gen. et sp. indet. 1, Neoselachii gen. et sp. indet. 2 and Hexanchidae? gen. et sp. indet., and possibly a fourth one, Euselachii gen. et sp. indet., so that at least nine chondrichthyan taxa have been found from the Nimaigu section. From a paleogeographic point of view, the four chondrichthyans described herein are endemic taxa unknown outside South China.\u003c/p\u003e\n\u003cp\u003eThe newly described Euselachii gen. et sp. indet. has a grasping-swallowing dentition with cladodont-like crowns. It displays stronger protrusions of the crown than those of the previously reported Euselachii gen. et sp. indet (Li et al., 2022). Neoselachii gen. et sp. indet. 1 exhibit grasping type tooth characterized by a conical main cusp flanked by lateral cusplets, whereas Neoselachii gen. et sp. indet. 2 displays tearing type tooth featuring a slender main cusp with sharp cutting edges. Hexanchidae? gen. et sp. indet. exhibits an extensively labio-lingually compressed crown with triangular cusps, indicative of cutting-type teeth (Cappetta, 2012). Consequently, the newly described taxa possess grasping-swallowing, sharp-grasping and cutting-type dentition and support previous observations that the shark fauna from Nimaigu section lacks durophagous forms (Li et al., 2022), which makes it different from other Ladinian-Carnian shark assemblages that were predominantly represented by durophagous sharks (Chen et al., 2007; Pla et al., 2013; Manzanares et al., 2018; Manzanares et al., 2020).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDental histology\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe dental histology of Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 was examined using micro-CT scanning, allowing three-dimensional reconstruction. The dental histology of Neoselachii gen. et sp. indet. 2 and Hexanchidae? gen. et sp. indet. is not presented due to artificial damage and poor preservation. The crown dentine of both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 consists entirely of compact orthodentine, which enfolds the pulp cavity. An ascending pulp cavity is present within the main cusp of Neoselachii gen. et sp. indet. 1, indicating it is a typical orthodont tooth, whereas no ascending pulp cavity is observed in Euselachii gen. et sp. indet.. Porous osteodentine is present only in the root of these two taxa, which is illustrated by a dense network of vascular canals, including connective vascular canals and ascending vascular canals. However, Euselachii gen. et sp. indet. exhibits a single longitudinal vascular canal associated with a vascular plexus, whereas Neoselachii gen. et sp. indet. 1 possesses two longitudinal vascular canals and numerous transverse vascular canals.\u003c/p\u003e\n\u003cp\u003eThe non-neoselachian euselachian sharks comprise Hybodontiformes, Protacrodontoidea, Sphenacanthidae and some euselachians with uncertain affinities. Investigations focusing on the dental histology of hybodont sharks are comparatively abundant (e.g., Seilacher, 1943; Patterson, 1966; Johnson, 1981; Maisey, 1983; Heckert et al., 2007; Stumpf et al., 2021; Cicimurri et al., 2024). There are osteodont (e.g., \u003cem\u003eTribodus limae\u003c/em\u003e, Lane and Maisey, 2012), pseudoosteodont (e.g., \u003cem\u003eLissodus minimus\u003c/em\u003e, Patterson, 1966; \u003cem\u003eCrassodus reifi\u003c/em\u003e, Maisch and Matzke, 2016) and orthodont (e.g., \u003cem\u003ePalaeobates angustissimus\u003c/em\u003e, Patterson, 1966; \u003cem\u003eLissodus\u003c/em\u003e \u003cem\u003esardiniensis\u003c/em\u003e,Fischer et al., 2010) histotypes in hybodont sharks. Sometimes, both pseudoosteodont and orthodont histotypes may occur within the same hybodont species (Błażejowski, 2004). Comparatively, studies on dental histology of other non-neoselachian euselachian sharks remain scarce, and only osteodont and orthodont histotypes have been described so far (e.g., Ivanov et al., 2017; Ivanov et al., 2022; Ivanov, 2022). The Euselachii gen. et sp. indet. described here exhibits an orthodont tooth characterized of a large longitudinal vascular canal, rather than a pulp cavity/pulp cavities that run vertically in most orthodont teeth. A longitudinal vascular canal is also present in \u003cem\u003eGzhelodus serratus\u0026nbsp;\u003c/em\u003e(Protacrodontoidea, Euselachii) from the Late Carboniferous of Russia (Ivanov, 2022). Characterized by high, basally fused cusps, it lacks an ascending pulp cavity but exhibits a moderately developed longitudinal vascular canal accompanied by a few “dental tubules”. However, \u003cem\u003eGzhelodus serratus\u003c/em\u003e distinguishes itself from Euselachii gen. et sp. indet. by containing numerous transverse vascular canals. Another euselachian taxon, \u003cem\u003eDesinia radiata\u0026nbsp;\u003c/em\u003e(Sphenacanthidae, Euselachii) from the Middle-Late Permian of Russia, also possess longitudinal vascular canals (Ivanov et al., 2022). It has a high main cusp flanked by well-separated cusplets. However, it exhibits two slender longitudinal vascular canals, of which the upper one connects to a pulp cavity that extends to the top of the main cusp. Additionally, orthodont hybodont teeth with flat crown possesses a thick longitudinal vascular canal and lacks ascending pulp cavity as well (e.g., \u003cem\u003ePalaeobates angustissimus\u003c/em\u003e, Böttcher, 2024). The multicuspid teeth of the hybodont shark \u003cem\u003eLamarodus triangulus\u003c/em\u003e, characterized by low and bulky cusps, also features a large longitudinal vascular canal, yet lacks an ascending pulp cavity (Ivanov et al., 2020). In summary, the presence of a longitudinal vascular canal, unaccompanied by one or more ascending pulp cavities, seems to be independent of crown morphology.\u003c/p\u003e\n\u003cp\u003eIn neoselachian sharks, orthodont, pseudoosteodont and osteodont histotypes are present, and the pseudoosteodont histotype is the most widespread in extant sharks and believed to be the plesiomorphic condition (Moyer et al., 2015; Schnetz et al., 2016; Mollen and Hovestadt, 2018; Jambura et al., 2020, Malyshkina et al., 2020). GMPKU-P-4266 exhibits a baso-labial depression where several unroofed canals are present, reminiscent of the polyhemiaulacorhize vascularization characteristic of Synechodontiformes (Klug, 2010). The dental histology of Synechodontiformes is poorly understood, with studies limited to \u003cem\u003eRomphaidon\u003c/em\u003e,\u003cem\u003e\u0026nbsp;Synechodus\u0026nbsp;\u003c/em\u003eand \u003cem\u003eWimanodon\u003c/em\u003e (Mollen and Hovestadt, 2018; Jambura et al., 2020; Saugen et al., 2024). \u003cem\u003eRomphaidon\u0026nbsp;\u003c/em\u003eand\u003cem\u003e\u0026nbsp;Wimanodon\u0026nbsp;\u003c/em\u003eexhibit a pseudoosteodont histotype, whereas both orthodont and pseudoosteodont histotypes are known to coexist within the genus \u003cem\u003eSynechodus\u0026nbsp;\u003c/em\u003e(Mollen and Hovestadt, 2018; Jambura et al., 2020; Saugen et al., 2024). GMPKU-P-4266 displays an orthodont histotype with an ascending pulp cavity within the main cusp. Its vascular system resembles that of \u003cem\u003eSynechodus\u003c/em\u003e sp. from the Early Cretaceous of northern France, as both share the presence of longitudinal vascular canal, ascending pulp cavity, and transverse vascular canals (Mollen and Hovestadt, 2018). However, compared with GMPKU-P-4266, the longitudinal vascular canal of \u003cem\u003eSynechodus\u003c/em\u003e sp. is significantly narrower, and only a single longitudinal vascular canal is present. Besides, the meshed secondary vascular canals of \u003cem\u003eSynechodus\u003c/em\u003e sp. are not present in Neoselachii gen. et sp. indet. 1. Additionally, the polyhemiaulacorhize vascularization of Synechodontiformes is defined by the presence of unroofed canals within the labial depression on the basal face of the root (Klug, 2010; Cappetta, 2012). The detailed illustration and description of the three-dimensional vascular system in Synechodontiformes is helpful for a comprehensive understanding of this type of root vascularization.\u003c/p\u003e\n\n"},{"header":"Conclusion","content":"\u003cp\u003eFour endemic euselachian sharks comprising Euselachii gen. et sp. indet., Neoselachii gen. et sp. indet. 1, Neoselachii gen. et sp. indet. 2, and Hexanchidae? gen. et sp. indet. are described from the Ladinian-Carnian interval of the Zhuganpo Member, ‘Falang’ Formation in Guizhou and Yunnan Provinces. In the study, Hexanchidae? gen. et sp. indet. represent the only taxon may across the Ladinian-Carnian boundary, whereas Euselachii gen. et sp. indet. and both Neoselachii gen. et sp. indet. 1 and 2 are confined to the late Ladinian. Palaeoecologically, Euselachii gen. et sp. indet. exhibits grasping-and-swallowing dentition; Neoselachii gen. et sp. indet. 1 and 2 exhibit grasping type and tearing type tooth, respectively; and Hexanchidae? gen. et sp. indet. bears teeth adapted for cutting. These findings further confirm that the Ladinian-Carnian shark assemblage at the Nimaigu section was dominated primarily by non-durophagous sharks. From a histological point of view, both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 display an orthodont histotype. Euselachii gen. et sp. indet. possesses a large longitudinal vascular canal but lacks an ascending pulp cavity. This feature also occurs in hybodonts with both flat crowns and multicuspid crowns bearing well-developed cusps, suggesting that its presence may be independent of tooth morphology. Neoselachii gen. et sp. indet. 1 displays a vascularization somewhat similar to the polyhemiaulacorhize type of synechodontiform sharks; however, its internal vascular architecture differs from that of the Cretaceous \u003cem\u003eSynechodus\u003c/em\u003e sp. by the presence of two large longitudinal vascular canals.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank Chai Jun (Lecturer, Beijing City University), Liu Shuang (Assistant Researcher, National Natural History Museum of China), Yin Yalei (Lecturer, Shenyang Normal University), Dai Yanlin (PetroChina Kunlun Gas Co., Ltd. Beijing Branch) and Tetsuya Sato for their assistance in collecting rock samples; Xu Xiuping (staff of the Plant Science Facility of the Institute of Botany, Chinese Academy of Sciences) for conducting the micro-CT scanning of the samples, as well as Wang Mingcui for dissolving the rock samples and picking shark remains in the laboratory.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZS and JL organized and designed of the study; ZS and JL conducted field work and collected samples; SZ, JL and GC identified the fish remains and wrote the manuscript; SZ analysed CT data and reconstructed dental histology, All authors revised the paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was financially supported by the National Natural Science Foundation of China (42172009, 41920104001), China Geological Survey (121201102000150012-09) and Natural Science Basic Research Program of Shaanxi (2025JC-YBQN-409).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe micro-CT data and project files used in this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAndreev, P. S., \u0026amp; Cuny, G. (2012). New Triassic stem selachimorphs (Chondrichthyes, Elasmobranchii) and their bearing on the evolution of dental enameloid in Neoselachii. \u003cem\u003eJournal of Vertebrate Paleontology\u003c/em\u003e, 32(2): 255-266. https://doi.org/10.1080/02724634.2012.644646\u003c/li\u003e\n\u003cli\u003eBenton, M. J., Zhang, Q. Y., Hu, S. Z., Chen, Z. Q., Wen, W., Liu, J., Huang, J. Y., Zhou, C. Y., Xie, T., Tong, J. N., \u0026amp; Choo, B. (2013). Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass extinction. \u003cem\u003eEarth\u003c/em\u003e-\u003cem\u003eScience Reviews\u003c/em\u003e, 125, 199-243. https://doi.org/10.1016/j.earscirev.2013.05.014\u003c/li\u003e\n\u003cli\u003eBłażejowski, B. (2004). Shark teeth from the Lower Triassic of Spitsbergen and their histology. \u003cem\u003ePolish Polar Research\u003c/em\u003e, 25(2): 153-167.\u003c/li\u003e\n\u003cli\u003eB\u0026ouml;ttcher, R. (2024). Root resorption during tooth replacement in sharks-a unique character of the Hybodontiformes (Chondrichthyes, Elasmobranchii). \u003cem\u003ePalaeodiversity\u003c/em\u003e, 17(1): 121-194. https://doi.org/10.18476/pale.v17.a6\u003c/li\u003e\n\u003cli\u003eBonaparte, C. L. J. (1838). Selachorum tabula analytica. \u003cem\u003eNuovi Annali delle Scienze Naturali Bologna\u003c/em\u003e, 1: 195-214.\u003c/li\u003e\n\u003cli\u003eBurrow, C. J., Hovestadt, D. C., Hovestadt-Euler, M., Turner, S., \u0026amp; Young, G. C. (2008). New information on the Devonian shark \u003cem\u003eMcmurdodus\u003c/em\u003e, based on material from western Queensland, Australia. \u003cem\u003eActa Geologica Polonica\u003c/em\u003e, 58(2): 155-163.\u003c/li\u003e\n\u003cli\u003eCappetta, H. (2012).\u003cem\u003e \u003c/em\u003eChondrichthyes. Mesozoic and Cenozoic Elasmobranchii: teeth. In Schultze H.P. (Ed.), \u003cem\u003eHandbook of Paleoichthyology\u003c/em\u003e (Volume 3E). M\u0026uuml;nchen: Friedrich Pfeil.\u003c/li\u003e\n\u003cli\u003eCappetta, H., \u0026amp; Grant-Mackie, J. (2018). Discovery of the most ancient \u003cem\u003eNotidanodon\u003c/em\u003e tooth (Neoselachii: Hexanchiformes) in the Late Jurassic of New Zealand. New considerations on the systematics and range of the genus. \u003cem\u003ePalaeovertebrata\u003c/em\u003e, 42(1). https://doi.org/10.18563/pv.42.1.e1\u003c/li\u003e\n\u003cli\u003eChai, J., Ni, P. G., Zhou, M., Lu, H., Sun, Z. Y., \u0026amp; Jiang, D. Y. (2019). Palaeoenvironment analysis of the Lower Fossil Assemblage of Middle Triassic Xingyi Fauna, Xingyi City, Guizhou Province. \u003cem\u003eJournal of Stratigraphy\u003c/em\u003e, 43(3): 29-42 (in Chinese with English abstract). https://doi.org/10.19839/j.cnki.dcxzz.2019.03.003\u003c/li\u003e\n\u003cli\u003eChen, L. D. (2002). New data of Middle-Late Triassic elasmobranch ichthyoliths from \u0026ldquo;Falang Formation\u0026rdquo; in Guanling, Guizhou.\u003cem\u003e Acta Micropalaeontologica Sinica\u003c/em\u003e, 19: 276-287 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eChen, L. D., \u0026amp; Cuny, G. (2003). Discovery of the Middle-Late Triassic elasmobranch ichthyoliths from Guanling area, Guizhou, SW China. \u003cem\u003eGeological Bulletin of China\u003c/em\u003e,22(4): 236-247.\u003c/li\u003e\n\u003cli\u003eChen, L. D., Cuny, G., \u0026amp; Wang, X. F. (2007). The chondrichthyan fauna from the Middle-Late Triassic of Guanling (Guizhou Province, SW China). \u003cem\u003eHistorical Biology\u003c/em\u003e, 19(4): 291-300. https://doi.org/10.1080/08912960701248234\u003c/li\u003e\n\u003cli\u003eCicimurri, D., Ciampaglio, C., Hoenig, M., Shell, R., Fuelling, L., Peterman, D., Cline, D. A., \u0026amp; Jacquemin, S. (2024). A description of the new hybodont shark genus, \u003cem\u003eColumnaodus\u003c/em\u003e, from the Burlington and Keokuk Limestones (Carboniferous, Mississippian, Osagean) of Illinois and Iowa, USA. \u003cem\u003eDiversity\u003c/em\u003e, 16(5): 276. https://doi.org/10.3390/d16050276\u003c/li\u003e\n\u003cli\u003eCompagno, L. J. V. (1973). Interrelationships of living elasmobranchs. \u003cem\u003eZoological\u003c/em\u003e \u003cem\u003eJournal of the Linnean Society\u003c/em\u003e, 53: 15-61.\u003c/li\u003e\n\u003cli\u003eCompagno, L. J. V. (1977). Phyletic relationships of living sharks and rays. \u003cem\u003eAmerican\u003c/em\u003e \u003cem\u003eZoologist\u003c/em\u003e, 17(02): 303-322.\u003c/li\u003e\n\u003cli\u003eCuny, G., Rieppel, O., \u0026amp; Sander, P. M. (2001). The shark fauna from the Middle Triassic (Anisian) of north-western Nevada. \u003cem\u003eZoological Journal of the Linnean Society\u003c/em\u003e, 133(3): 285-301. https://doi.org/10.1006/zjls.2000.0273\u003c/li\u003e\n\u003cli\u003ede Buen, F. (1926). Cat\u0026aacute;logo ictiol\u0026oacute;gico del Mediterr\u0026aacute;neo espa\u0026ntilde;ol y de Marruecos, recopilando lo publicado sobre peces de las costas mediterr\u0026aacute;nea y pr\u0026oacute;ximas del Atl\u0026aacute;ntico (Mar de Espa\u0026ntilde;a). In de Buen, O. (Ed.), \u003cem\u003eResultados de las campa\u0026ntilde;as realizadas por acuerdos internacionales\u003c/em\u003e (N\u0026uacute;m. 2). Spain: Instituto Espa\u0026ntilde;ol de Oceanograf\u0026iacute;a.\u003c/li\u003e\n\u003cli\u003eDuffin, C. J., \u0026amp; Ward, D. J. (1983). Neoselachian sharks\u0026apos; teeth from the Lower Carboniferous of Britain and the Lower Permian of the U.S.A. \u003cem\u003ePalaeontology\u003c/em\u003e, 26(1): 93-110.\u003c/li\u003e\n\u003cli\u003eDuffin, C. J., Richter, M., \u0026amp; Neis, P. A. (1996). Shark remains from the late Carboniferous of the Amazon Basin, Brazil. \u003cem\u003eNeues Jahrbuch f\u0026uuml;r Geologie und Pal\u0026auml;ontologie\u003c/em\u003e, \u003cem\u003eMonatshefte\u003c/em\u003e, 4: 232-256. https://doi.org/10.1127/njgpm/1996/1996/232\u003c/li\u003e\n\u003cli\u003eEnos, P., Wei, J. Y., \u0026amp; Lehrmann, D. J. (1998). Death in Guizhou\u0026mdash;Late Triassic drowning of the Yangtze carbonate platform. \u003cem\u003eSedimentary Geology\u003c/em\u003e, 118(1-4): 55-76. https://doi.org/10.1016/S0037-0738(98)00005-0\u003c/li\u003e\n\u003cli\u003eFang, G. Y., Sun, Y. L., Ji, C., \u0026amp; Wu, F. X. (2023). First record of \u003cem\u003eSaurichthys\u003c/em\u003e (Actinopterygii: Saurichthyidae) from the Late Triassic of eastern Paleo-Tethys. \u003cem\u003eVertebrata PalAsiatica\u003c/em\u003e, 61(1): 1-16. https://doi.org/10.19615/j.cnki.2096-9899.221013.\u003c/li\u003e\n\u003cli\u003eFischer, J., Schneider, J. W., \u0026amp; Ronchi, A. (2010). New hybondontoid shark from the Permocarboniferous (Gzhelian-Asselian) of Guardia Pisano (Sardinia, Italy). \u003cem\u003eActa Palaeontologica Polonica\u003c/em\u003e, 55(2): 241-264. http://dx.doi.org/10.4202/app.2009.0019\u003c/li\u003e\n\u003cli\u003eGinter, M., Hampe, O., \u0026amp; Duffin, C.J. (2010). Chondrichthyes (Paleozoic Elasmobranchii: teeth). In H.P. Schultze (Ed.), \u003cem\u003eHandbook of Paleoichthyology\u003c/em\u003e (Volume 3D). M\u0026uuml;nchen: Friedrich Pfeil.\u003c/li\u003e\n\u003cli\u003eGray, J. E. (1851). \u003cem\u003eList of the Specimens of Fish in the Collection of the British Museum\u003c/em\u003e: \u003cem\u003ePart\u003c/em\u003e \u003cem\u003eI\u003c/em\u003e., \u003cem\u003eChondropterygii\u003c/em\u003e. London: Printed by order of the Trustees, British Museum.\u003c/li\u003e\n\u003cli\u003eHay, O. P. (1902). Bibliography and catalogue of the fossil vertebrate of North America. \u003cem\u003eBulletin of the United States Geological Survey\u003c/em\u003e, 179: 1-868.\u003c/li\u003e\n\u003cli\u003eHeckert, A. B., Ivanov, A., \u0026amp; Lucas, S. G. (2007). Dental morphology of the hybodontoid shark \u003cem\u003eLonchidion humblei\u003c/em\u003e Murry from the Upper Triassic Chinle Group, USA. \u003cem\u003eNew Mexico Museum of Natural History and Science Bulletin\u003c/em\u003e, 41: 45-48.\u003c/li\u003e\n\u003cli\u003eHerman, J., Hovestadt-Euler, M., \u0026amp; Hovestadt, D. C. (1990). Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living superspecific taxa of chondrichthyan fishes. Part A: Selachii. No. 2b: Order: Carcharhiniformes-Familiy: Scyliorhinidae. \u003cem\u003eBulletin de l\u0026rsquo;Institut royal des Sciences naturelles de Belgique\u003c/em\u003e, \u003cem\u003eBiologie\u003c/em\u003e, 60: 181-230.\u003c/li\u003e\n\u003cli\u003eHuxley, T. H. (1880). On the application of the laws of evolution to the arrangement of the Vertebrata, and more particularly of the Mammalia. \u003cem\u003eProceedings of the Zoological Society of London\u003c/em\u003e, 1880: 649-662.\u003c/li\u003e\n\u003cli\u003eIvanov, A. O. (2022). New late Carboniferous chondrichthyans from the European Russia. \u003cem\u003eBulletin of Geosciences\u003c/em\u003e, 97(2): 219-234. https://doi.org/10.3140/bull.geosci.1845\u003c/li\u003e\n\u003cli\u003eIvanov, A. O., \u0026amp; Duffin, C. J. (2024). Late Palaeozoic anachronistid chondrichthyans. \u003cem\u003eHistorical Biology\u003c/em\u003e, 1-19. https://doi.org/10.1080/08912963.2024.2388208\u003c/li\u003e\n\u003cli\u003eIvanov, A. O., Duffin, C. J., \u0026amp; Naugolnykh, S. V. (2017). A new euselachian shark from the early Permian of the Middle Urals, Russia. \u003cem\u003eActa Palaeontologica Polonica\u003c/em\u003e, 62(2): 290-298. https://doi.org/10.4202/app.00347.2017\u003c/li\u003e\n\u003cli\u003eIvanov, A. O., Kovalenko, E. S., Murashev, M. M., \u0026amp; Podurets, K. M. (2022). Euselachian sharks (Elasmobranchii, Chondrichthyes) from the Middle and Late Permian of European Russia. \u003cem\u003ePaleontological Journal\u003c/em\u003e, 56(11): 1372-1384. https://doi.org/10.1134/S0031030122110065\u003c/li\u003e\n\u003cli\u003eIvanov, A. O., Nestell, M. K., Nestell, G. P., \u0026amp; Bell Jr, G. L. (2020). New fish assemblages from the Middle Permian from the Guadalupe Mountains, West Texas, USA. \u003cem\u003ePalaeoworld\u003c/em\u003e, 29(2): 239-256. https://doi.org/10.1016/j.palwor.2018.10.003\u003c/li\u003e\n\u003cli\u003eJambura, P. L., T\u0026uuml;rtscher, J., Kindlimann, R., Metscher, B., Pfaff, C., Stumpf, S., Weber, G. W., \u0026amp; Kriwet, J. (2020). Evolutionary trajectories of tooth histology patterns in modern sharks (Chondrichthyes, Elasmobranchii). \u003cem\u003eJournal of Anatomy\u003c/em\u003e, 236(5): 753-771. https://doi.org/10.1111/joa.13145\u003c/li\u003e\n\u003cli\u003eJiang, D. Y., Motani, R., Li, C., Hao, W. C., Sun, Y. L., Sun, Z. Y., \u0026amp; Schmitz, L. (2005). Guanling Biota: a marker of Triassic biotic recovery from the end-Permian extinction in the ancient Guizhou sea. \u003cem\u003eActa Geologica Sinica\u003c/em\u003e, 79(6): 729-738. https://doi.org/10.1111/j.1755-6724.2005.tb00926.x\u003c/li\u003e\n\u003cli\u003eJiang, D. Y., Zhou, M., Motani, R., Tintori, A., Fraser, N. C., Huang, J. D., Rieppel, O., Ji, C., Fu, W. L., Sun, Z. Y., \u0026amp; Lu, H. (2023). Emergence and ecological transition of the Mesozoic marine reptiles: evidence from the Early Triassic Chaohu and the Middle Triassic Xingyi faunas. \u003cem\u003ePalaeogeography\u003c/em\u003e, \u003cem\u003ePalaeoclimatology\u003c/em\u003e, \u003cem\u003ePalaeoecology\u003c/em\u003e, 628, 111750. https://doi.org/10.1016/j.palaeo.2023.111750\u003c/li\u003e\n\u003cli\u003eJohnson, G. D. (1981). Hybodontoidei (Chondrichthyes) from the Wichita-albany Group (Early Permian) of Texas. \u003cem\u003eJournal of Vertebrate Paleontology\u003c/em\u003e, 1(1): 1-41.\u003c/li\u003e\n\u003cli\u003eKlug, S. (2010). Monophyly, phylogeny and systematic position of the Synechodontiformes (Chondrichthyes, Neoselachii). \u003cem\u003eZoologica Scripta\u003c/em\u003e, 39(1): 37-49. https://doi.org/10.1111/j.1463-6409.2009.00399.x\u003c/li\u003e\n\u003cli\u003eKoot, M. B., Cuny, G., Orchard, M. J., Richoz, S., Hart, M. B., \u0026amp; Twitchett, R. J. (2015). New hybodontiform and neoselachian sharks from the Lower Triassic of Oman. \u003cem\u003eJournal of Systematic Palaeontology\u003c/em\u003e, 13(10): 891-917. https://doi.org/10.1080/14772019.2014.963179\u003c/li\u003e\n\u003cli\u003eLane, J. A., \u0026amp; Maisey, J. G. (2012). The visceral skeleton and jaw suspension in the durophagous hybodontid shark \u003cem\u003eTribodus limae\u003c/em\u003e from the Lower Cretaceous of Brazil. \u003cem\u003eJournal of Paleontology\u003c/em\u003e, 86(5): 886-905. https://doi.org/10.1016/j.jsames.2014.04.002\u003c/li\u003e\n\u003cli\u003eLi, J. C., Sun, Z. Y., Cuny, G., Ji, C., Jiang, D. Y., \u0026amp; Zhou, M. (2022). An unusual shark assemblage from the Ladinian-Carnian interval of South China. \u003cem\u003ePapers in Palaeontology\u003c/em\u003e, 8(1): e1404. https://doi.org/10.1002/spp2.1404\u003c/li\u003e\n\u003cli\u003eLi, Y. X., Xiao, J. F., Wei, J. Y., \u0026amp; Lehrmann, D. J. (2005). Ladinian-Carnian transgression and the evolution of Yangtze Carbonate Platform in southwestern Guizhou. \u003cem\u003eActa Geoscientica Sinica\u003c/em\u003e, 26(2): 249-253 (in Chinese with English abstract). https://doi.org/10.1111/1755-6724.2005.tb00926.x\u003c/li\u003e\n\u003cli\u003eLi, Z. G., Sun, Z. Y., Jiang, D. Y., \u0026amp; Ji, C. (2016). LA-ICP-MS Zircon U-Pb age of the fossil layer of Triassic Xingyi Fauna from Xingyi, Guizhou, and its significance. \u003cem\u003eGeological Review\u003c/em\u003e, 62(3): 779-790 (in Chinese with English abstract). https://doi.org/10.16509/j.georeview.2016.03.018\u003c/li\u003e\n\u003cli\u003eLu, H., Jiang, D. Y., Motani, R., Ni, P. G., Sun, Z. Y., Tintori, A., Xiao, S. Z., Zhou, M., Ji, C., \u0026amp; Fu, W. L. (2018). Middle Triassic Xingyi Fauna: showing turnover of marine reptiles from coastal to oceanic environments. \u003cem\u003ePalaeoworld\u003c/em\u003e, 27, 107-116. https://doi.org/10.1016/j.palwor.2017.05.005\u003c/li\u003e\n\u003cli\u003eMa, L. T., Ji, C., Sun, Z. Y., Yang, P. F., \u0026amp; Zou, X. D. (2013). Biodiversity and stratigraphic distribution of the Triassic Xingyi marine reptile fauna, Guizhou Province. \u003cem\u003eJournal of Stratigraphy\u003c/em\u003e, 37(2): 178-185 (in Chinese with English abstract). https://doi.org/10.19839/j.cnki.dcxzz.2013.02.006\u003c/li\u003e\n\u003cli\u003eMaisch, M. W., \u0026amp; Matzke, A. T. (2016). A new hybodontid shark (Chondrichthyes, Hybodontiformes) from the lower Jurassic Posidonienschiefer Formation of Dotternhausen, SW Germany. \u003cem\u003eNeues Jahrbuch f\u0026uuml;r Geologie und Pal\u0026auml;ontologie\u003c/em\u003e, \u003cem\u003eAbhandlungen\u003c/em\u003e, 280(3): 241-257. https://doi.org/10.1127/njgpa/2016/0577\u003c/li\u003e\n\u003cli\u003eMaisey, J. G. (1983). Cranial anatomy of \u003cem\u003eHybodus basanus\u003c/em\u003e Egerton from the Lower Cretaceous of England. \u003cem\u003eAmerican Museum Novitates\u003c/em\u003e, 2758: 1-64.\u003c/li\u003e\n\u003cli\u003eMalyshkina, T. P., Jagt-Yazykova, E. A., Kolchanov, V. V., \u0026amp; Nazarkin, M. V. (2020). First shark record from the Upper Cretaceous of the Kuril Islands, Far East Russia. \u003cem\u003eCretaceous Research\u003c/em\u003e, 115: 104551. https://doi.org/10.1016/j.cretres.2020.104551\u003c/li\u003e\n\u003cli\u003eManzanares, E., Escudero-Mozo, M. J., Ferr\u0026oacute;n, H., Mart\u0026iacute;nez-P\u0026eacute;rez, C., \u0026amp; Botella, H. (2020). Middle Triassic sharks from the Catalan Coastal Ranges (NE Spain) and faunal colonization patterns during the westward transgression of Tethys. \u003cem\u003ePalaeogeography\u003c/em\u003e, \u003cem\u003ePalaeoclimatology\u003c/em\u003e, \u003cem\u003ePalaeoecology\u003c/em\u003e, 539: 109489. https://doi.org/10.1016/j.palaeo.2019.109489\u003c/li\u003e\n\u003cli\u003eManzanares, E., Pla, C., Ferr\u0026oacute;n, H. G., \u0026amp; Botella, H. (2018). Middle-Late Triassic chondrichthyans remains from the Betic Range (Spain). \u003cem\u003eJournal of Iberian Geology\u003c/em\u003e, 44: 129-138. https://doi.org/10.1007/s41513-017-0027-1\u003c/li\u003e\n\u003cli\u003eMollen, F. H., \u0026amp; Hovestadt, D. C. (2018). A new partial skeleton of a palaeospinacid shark (Neoselachii, Synechodontiformes) from the Albian of northern France, with a review of the taxonomic history of Early Cretaceous species of \u003cem\u003eSynechodus\u003c/em\u003e Woodward, 1888. \u003cem\u003eGeodiversitas\u003c/em\u003e, 40(4): 557-574. https://doi.org/10.5252/geodiversitas2018v40a25\u003c/li\u003e\n\u003cli\u003eMoyer, J. K., Riccio, M. L., \u0026amp; Bemis, W. E. (2015). Development and microstructure of tooth histotypes in the blue shark, \u003cem\u003ePrionace glauca\u003c/em\u003e (Carcharhiniformes: Carcharhinidae) and the great white shark, \u003cem\u003eCarcharodon carcharias\u003c/em\u003e (Lamniformes: Lamnidae). \u003cem\u003eJournal of Morphology\u003c/em\u003e, 276(7): 797-817. https://doi.org/10.1002/jmor.20380\u003c/li\u003e\n\u003cli\u003ePatterson, C. (1966). British Wealden sharks. \u003cem\u003eBulletin of the British Museum\u003c/em\u003e (\u003cem\u003eNatural History\u003c/em\u003e), 11: 283-350. \u003c/li\u003e\n\u003cli\u003ePla, C., M\u0026aacute;rquez-Aliaga, A., \u0026amp; Botella, H. (2013). The chondrichthyan fauna from the Middle Triassic (Ladinian) of the Iberian Range (Spain). \u003cem\u003eJournal of Vertebrate Paleontology\u003c/em\u003e, 33(4): 770-785. https://doi.org/10.1080/02724634.2013.748668\u003c/li\u003e\n\u003cli\u003eSaugen, S. M., Roberts, A. J., Engelschi\u0026oslash;n, V. S., \u0026amp; Hurum, J. H. (2024). A new assemblage of Lower Triassic neoselachians (Chondrichthyes) from the Grippia Bonebed of Spitsbergen, Norway. \u003cem\u003eJournal of Vertebrate Paleontology\u003c/em\u003e, 44(3), e2426544. https://doi.org/10.1080/02724634.2024.2426544\u003c/li\u003e\n\u003cli\u003eSchnetz, L., Pfaff, C., \u0026amp; Kriwet, J. (2016). Tooth development and histology patterns in lamniform sharks (Elasmobranchii, Lamniformes) revisited. \u003cem\u003eJournal of Morphology\u003c/em\u003e, 277(12): 1584-1598. https://doi.org/10.1002/jmor.20597\u003c/li\u003e\n\u003cli\u003eSeilacher, A. (1943). Elasmobranchier-Reste aus dem oberen Muschelkalk und dem Keuper W\u0026uuml;rttembergs. \u003cem\u003eNeues Jahrbuch f\u0026uuml;r Mineralogie\u003c/em\u003e, \u003cem\u003eGeologie und Pal\u0026auml;ontologie\u003c/em\u003e, \u003cem\u003eMonatshefte B\u003c/em\u003e, 1943: 256-292.\u003c/li\u003e\n\u003cli\u003eStumpf, S., L\u0026oacute;pez‐Romero, F. A., Kindlimann, R., Lacombat, F., Pohl, B., \u0026amp; Kriwet, J. (2021). A unique hybodontiform skeleton provides novel insights into Mesozoic chondrichthyan life. \u003cem\u003ePapers in Palaeontology\u003c/em\u003e, 7(3): 1479-1505. https://doi.org/10.1002/spp2.1350\u003c/li\u003e\n\u003cli\u003eThies, D., Vespermann, J., \u0026amp; Solcher, J. (2014). Two new neoselachian sharks (Elasmobranchii, Neoselachii, Synechodontiformes) from the Rhaetian (Late Triassic) of Europe. \u003cem\u003ePalaeontographica\u003c/em\u003e, \u003cem\u003eAbteilung A\u003c/em\u003e, 303(4-6): 137-167. https://doi.org/10.1127/pala/303/2014/137\u003c/li\u003e\n\u003cli\u003eTintori, A., Sun, Z. Y., Ni, P. G., Lombardo, C., Jiang, D. Y., \u0026amp; Motani, R. (2015). Oldest stem Teleostei from the late Ladinian (Middle Triassic) of southern China. \u003cem\u003eRivista Italiana di Paleontologia e Stratigrafia\u003c/em\u003e, 121(3): 285-296. https://doi.org/10.13130/2039-4942/6519\u003c/li\u003e\n\u003cli\u003eUnderwood, C. J., Mitchell, S. F., \u0026amp; Veltkamp, C. J. (1999). Microborings in mid-Cretaceous fish teeth. \u003cem\u003eProceedings of the Yorkshire Geological Society\u003c/em\u003e, 52(3): 269-274. https://doi.org/10.1144/pygs.52.3.269\u003c/li\u003e\n\u003cli\u003eUnderwood, C. J., \u0026amp; Ward, D. J. (2004). Neoselachian sharks and rays from the British Bathonian (Middle Jurassic). \u003cem\u003ePalaeontology\u003c/em\u003e, 47(3): 447-501. https://doi.org/10.1111/j.0031-0239.2004.00386.x\u003c/li\u003e\n\u003cli\u003eUnderwood, C. J., \u0026amp; Ward, D. J. (2008). Sharks of the Order Carcharhiniformes from the British Coniacian, Santonian and Campanian (Upper Cretaceous). \u003cem\u003ePalaeontology\u003c/em\u003e, 51(3): 509-536. https://doi.org/10.1111/j.1475-4983.2008.00757.x\u003c/li\u003e\n\u003cli\u003eWang, X. F., Bachmann, G., Hans, H., Sander, P., Cuny, G., Chen, X. H., Wang, C. S., Chen, L. D., Cheng, L., Meng, F. S., \u0026amp; Xu, G. H. (2008). The Late Triassic black shales of the Guanling area, Guizhou Province, South-west China: a unique marine reptile andpelagic crinoid fossil lagerstatte. \u003cem\u003ePalaeontology\u003c/em\u003e, 51 (1), 27-61. https://doi.org/10.1111/j.1475-4983.2007.00735.x\u003c/li\u003e\n\u003cli\u003eYin, H. F. (1982). Discussion on the Ladinian stage in China. \u003cem\u003eGeological Review\u003c/em\u003e, 28(3): 235-239 (in Chinese with English abstract).\u003c/li\u003e\n\u003cli\u003eZhang, B. M., Chen, X. H., Cheng, L., \u0026amp; Zhang, M. (2012). Middle Triassic (Ladinian) elasmobranch scales from the southwestern Guizhou, China. \u003cem\u003eActa Micropalaeontologica Sinica\u003c/em\u003e, 29(1): 52-61 (in Chinese with English abstract). https://doi.org/10.1007/s11783-011-0280-z\u003c/li\u003e\n\u003cli\u003eZhang, Z. T., \u0026amp; Sun, Y. D. (2023). The Ladinian-Carnian conodont fauna at Yize, Yunnan, southwestern China, with implications for conodont palaeoecology and palaeogeography. \u003cem\u003eGeological Magazine\u003c/em\u003e, 160(4): 776-793. https://doi.org/10.1017/S0016756822001236\u003c/li\u003e\n\u003cli\u003eZou, X. D., Balini, M., Jiang, D. Y., Tintori, A., Sun, Z. Y., \u0026amp; Sun, Y. L. (2015a). Ammonoids from the Zhuganpo Member of the Falang Formation at Nimaigu and their relevance for dating the Xingyi fossil-lagerst\u0026auml;tte (late Ladinian, Guizhou, China). \u003cem\u003eRivista Italiana di Paleontologia e Stratigrafia\u003c/em\u003e, 121(2): 135-161. https://doi.org/10.13130/2039-4942/6511\u003c/li\u003e\n\u003cli\u003eZou, X. D., Guo, W., Jiang, D. Y., \u0026amp; Sun, Z. Y. (2015b). Preliminary analysis of environment of fossils reservoir of Xingyi Fauna in Guizhou Province. \u003cem\u003eActa Scientiarum Naturalium Universitatis Pekinensis\u003c/em\u003e, 51(3): 472-484 (in Chinese with English abstract). https://doi.org/10.13209/j.0479-8023.2014.179\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Chondrichthyans, Euselachii, Vascular system, Histology, Triassic","lastPublishedDoi":"10.21203/rs.3.rs-7193674/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7193674/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA taxonomic study of four tooth genera of euselachian sharks from the Ladinian-Carnian interval of the Guizhou and Yunnan Provinces, South China is presented. They include one euselachian shark of uncertain affinity, two indeterminate neoselachian sharks and one potential hexanchid shark. These four taxa display non-durophagous feeding behaviors, including grasping-swallowing, grasping, tearing and cutting strategies. High-resolution micro-CT scans reveal that both Euselachii gen. et sp. indet. and Neoselachii gen. et sp. indet. 1 possess orthodont teeth. Euselachii gen. et sp. indet. exhibits a prominent longitudinal vascular canal but lacks an ascending pulp cavity, while Neoselachii gen. et sp. indet. 1 features two longitudinal vascular canals and a vascular cavity that ascends into the main cusp.\u003c/p\u003e","manuscriptTitle":"New euselachian teeth from the Ladinian-Carnian interval of Guizhou and Yunnan Provinces, South China","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-29 11:39:51","doi":"10.21203/rs.3.rs-7193674/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5b08e227-e4b9-4b37-a7e5-0a023a754207","owner":[],"postedDate":"July 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-28T18:38:57+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-29 11:39:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7193674","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7193674","identity":"rs-7193674","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}