Presence of Eodiscida (Trilobita) in the Cambrian Series 2 of the Iberian Chains (Northeast Spain)

Presence of Eodiscida (Trilobita) in the Cambrian Series 2 of the Iberian Chains (Northeast Spain) | 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 Presence of Eodiscida (Trilobita) in the Cambrian Series 2 of the Iberian Chains (Northeast Spain) Alexandre Sepúlveda, Juan Chirivella Martorell, Eladio Liñán, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8653291/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract The Cambrian Series 2 of the Iberian Peninsula is characterised by strong trilobite faunal endemism, which has hindered both regional and intercontinental correlations. In the Iberian Chains (Northeast Spain), the Marianian regional stage deposits of the Ribota and Huérmeda formations contain a trilobite fauna that is still insufficiently studied, despite its considerable biostratigraphic potential. This study documents the occurrence of the globally distributed Eodiscida in the lower part of the Huérmeda Formation (upper Marianian; base of the Stage 4 of the Cambrian). Morphometric analyses of cranidial shape demonstrate that specimens previously tentatively assigned to Hebediscus represent a new species, Hebediscus carlsi n. sp. Additional material from the same horizon is tentatively assigned to Hebediscina , constituting the first record of this genus in the Iberian Peninsula. The presence of Hebediscus and Hebediscina provides a robust basis for correlating the lower part of the Huérmeda Formation with coeval horizons in the West Gondwana margin, Avalonia, Siberia, Central Asian Orogenic Belt, and Australia, contributing to improved regional and intercontinental correlation of Cambrian Series 2 strata. trilobites geometric morphometrics systematics biostratigraphy upper Marianian (Cambrian Stage 4 Cambrian Series 2) Iberian Chains (NE Spain) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The strong endemism of Cambrian Series 2 trilobite faunas, and the resulting lack of intercontinental faunal connections, has hindered the formal ratification of this series and of Stages 3 and 4 of the Cambrian. These correlation difficulties have also affected the correlation of the regional stages of the Iberian Peninsula for this interval, traditionally including the Ovetian, Marianian and Bilbilian stages (Sdzuy, 1971 ; Liñán et al., 1993 , 2002 , 2004 ; Shergold, 1997 ; Gozalo et al., 2003 , 2008 ; Sundberg et al., 2016 ; Geyer, 2019 ; Peng et al., 2020 ). Therefore, the markers used to define the boundaries between these stages have been revised repeatedly (Sdzuy, 1971 ; Liñán and Gámez-Vintaned, 1993 ; Liñán et al., 1993 , 1996 , 2002 , 2004 ). In recent years, several authors have been working on the establishment of more robust correlations across the Iberian Peninsula, especially in the Marianian stage (Collantes et al., 2022 ; Liñán et al., 2024 ; Sepúlveda et al., 2024 ). In the Iberian Chains (Northeast Spain), one of the regions of the Iberian Peninsula with extensive Cambrian outcrops, the Marianian deposits are comprised in the Ribota and Huérmeda formations. Compared with other Cambrian intervals in this area, the trilobite fauna from this stratigraphic interval has remained relatively poorly studied, and only a limited number of works have addressed its systematics and biostratigraphy (Richter and Richter, 1948 ; Sdzuy, 1961 ; Liñán et al., 2003 ; Sepúlveda et al., 2018 , 2021 , 2022 , 2025 in press; Álvaro et al., 2019 ; Collantes et al., 2024 ). One of the most characteristic fossiliferous horizons within this interval occurs at the lower part of the Huérmeda Formation (see Lotze, 1961 ; Sdzuy, 1961 ), which has been correlated with the base of the upper Marianian. Trilobites from this horizon have recently been the focus of several detailed systematic studies (see Sepúlveda et al., 2018 , 2021 , 2022 , 2025 in press; Álvaro et al., 2019 ; Collantes et al., 2024 ). However, most of the taxa studied in these works have relatively limited potential for regional and intercontinental correlation The present study addresses the occurrence of the globally distributed Eodiscida Kobayashi, 1939 in the lower part of the Huérmeda Formation. Morphometric analyses of the cranidial morphology of specimens tentatively assigned to Hebediscus Whitehouse, 1936 by Sepúlveda et al. ( 2022 ), together with newly collected material and data from species of the genus from other regions, indicate that these specimens represent a distinct species, Hebediscus carlsi n. sp. The new species is characterised by a narrow (tr.) glabella with a subtruncate anterior glabellar margin, a short (sag.) preglabellar area, and a slightly curved anterior cranidial margin. Additional specimens from the same stratigraphic horizon display a different morphology and are tentatively assigned to the closely related genus Hebediscina Rasetti, 1972 , representing the first record of this genus in the Iberian Peninsula. Hebediscus has long been regarded as a key taxon for intercontinental correlation of the base of Cambrian Stage 4 (Geyer and Shergold, 2000 ; Geyer, 2005 ; Sundberg et al., 2016 ), with the majority of species occurring near this level across several palaeocontinents, including West Gondwana, Avalonia, Siberia, and Central Asian Orogenic Belt. The genus also provides an important correlation tool along the West Gondwana margin, having been reported from comparable stratigraphic positions in the Ossa-Morena area of the Iberian Peninsula and the Sectigena Zone of Morocco. Furthermore, Hebediscina has been recorded from a horizon equivalent to the lower part of the Huérmeda Formation in Australia. Geological and stratigraphic setting The material studied herein comes from the municipalities of Tierga and Mesones de Isuela, located in the northern sector of the Iberian Chains (Fig. 1 b), one of the areas of the Iberian Peninsula with extensive exposure of Palaeozoic rocks (Fig. 1 a). The Iberian Chains consists of two northwest-southwest parallel strings separated by the Tertiary Calatayud basin and form part of the Cantabrian and West-Asturian Leonese zones of the Iberian Peninsula (Gozalo and Liñán, 1988 ). The Iberian Chains are divided into the Badules, Mesones, and Herrera tectonostratigraphic units by the Jarque and Datos faults. The Cambrian Series 2 lithostratigraphic sequence of the Iberian Chains comprises, in ascending order, the Bámbola, Embid, Jalón, Ribota, Huérmeda, Daroca, and Valdemiedes formations (see Lotze, 1961 ; Schmidt-Thomé, 1973 ; Liñán et al., 1996 , 2002 , 2004 ; Gozalo et al., 2008 ). The specimens examined in this study were collected from the lower part of the Huérmeda Formation, in the level 23 of the Minas Tierga-1 (MT1) section, and levels 2 and 3 of the Mesones-9 (M9) section (Fig. 2 ), both located within the Mesones Unit. The stratigraphy of the MT1 section and the systematics of part of its trilobite fauna were presented by Sepúlveda et al. ( 2021 , 2022 ), with additional research provided by Collantes et al. ( 2024 ) and Sepúlveda et al. ( 2025 in press). Sepúlveda et al. ( 2022 ) also documented the stratigraphy of the M9 section and studied its trilobite fauna. The systematics of several species from this horizon from nearby sections was also examined by Álvaro et al. ( 2019 ). The Huérmeda Formation consists of a succession of green to dark blue shales, weathering to brown or blackish colours, and minor intercalations of yellow dolostone, marl, and sandstone. The base of this formation is readily identified above the upper massive dolostone bank of the Ribota Formation. The transition between the two formations is gradual, as thin dolostone beds occur in the lower part of the Huérmeda Formation in various sections and areas (see Scheuplein, 1967 ; Aliaga, 1968 ; Schmidt-Thomé, 1968 , 1973 ; Schmitz, 1971 ). The fine-grained detrital sediments of the Huérmeda Formation have been interpreted as having been deposited in an open-shelf sublittoral environment (Gámez et al., 1991 ; Álvaro et al., 1995 ). The trilobite-bearing shale facies in the lower part of this formation are indicative of more open marine conditions (Álvaro et al., 1995 ), which are also reflected in the wide geographical distribution of several taxa recorded from this horizon (see Sdzuy, 1961 , 1971 ; Álvaro et al., 2019 ; Sepúlveda et al., 2022 ; herein). Morphometric analysis A landmark-based geometric morphometric analysis was conducted to assess the cranidial shape affinities between specimens of Hebediscus carlsi n. sp. from the lower part of the Huérmeda Formation and species of the genus from other regions. The dataset comprises 46 specimens representing several species, including H . granulosus Lazarenko, 1962 , H. sublongus Korovnikov, 2007 d vagus Egorova in Egorova and Savitskiy, 1969 from Siberia; H . lemdadensis Geyer, 1988 from Morocco; H . planus (Hutchinson, 1962 ) and H . williamsi Westrop and Landing, 2011 from Newfoundland; multiple specimens assigned to H . attleborensis (Shaler and Foerste in Shaler, 1888 ) from Massachusetts, Morocco, Newfoundland, and Siberia (see Shaw, 1950 ; Hupé, 1953 ; Egorova and Savitskiy, 1969 ; Fletcher, 2006 ; Fletcher and Theokritoff, 2008 ; Rozanov and Varlamov, 2008 ); and Hebediscus carlsi n. sp. from the Huérmeda Formation. Several specimens of forms referred to Hebediscus in open nomenclature were also included, such as H . sp. 1 and H . sp. 2 from Newfoundland (see Westrop and Landing, 2011 ), and H . sp. indet. A and H . cf. lemdadensis from Morocco (see Geyer, 1988 ). The latter was subsequently reassigned to H . lemdadensis by Geyer ( 2005 ). The geographic origin of specimens assigned to H . attleborensis was controlled in order to evaluate the proposal that only the type material from Massachusetts should be retained within the species (see Westrop and Landing, 2011 ; Geyer and Landing, 2025 ). It should be noted that the specimen from Newfoundland assigned to H . attleborensis by Fletcher ( 2006 ) and Fletcher and Theokritoff ( 2008 ) was subsequently reassigned to H . sp. 1 by Westrop and Landing ( 2011 ). Several species assigned to Hebediscus , such as H . lermontovae Repina, 1960 , H. erbaensis Repina in Repina et al., 1964 , H. flexus Repina in Repina et al., 1964 , H. pokrovskayae Zadorozhnaya in Zhuravleva et al., 1967 , H. convexus Nikiforov in Repina et al., 1974 , H. durus Korobov, 1980 , as well as H . sp. indet. B sensu Geyer ( 1988 ) and specimens assigned to H . attleborensis by Repina ( 1972 ), were excluded from the analysis due to the poor preservation of the available cranidia. Details of specimen catalogue numbers and source publications for the images used in landmarking are provided in Supplementary Information 1 (SI1). Eight homologous anatomical landmarks (Fig. 3 ) were digitised on the available cranidia using TpsDig (Rohlf, 2009 , 2015 ). Prior to landmarking, images of specimens exhibiting oblique tectonic deformation were digitally retrodeformed using Adobe Photoshop. Specimens displaying strong sagittal or transverse compression were excluded from the analysis. Landmark coordinates were imported into the R environment (v. 4.3.2; R Core Team 2021 ) and analysed using the geomorph package (Adams and Otárola-Castillo, 2013 ). Landmarks were placed on the right side of the cranidia when possible; specimens landmarked on the left side were computationally mirrored prior to the analysis. Following Generalised Procrustes Alignment (GPA), a Principal Component Analysis (PCA) was performed on size-corrected Procrustes shape coordinates. Because a Procrustes regression of shape on centroid size revealed a significant heterogeneity of allometric slopes among species (logCS x species: F = 2.1079, p = 0.011), residuals were obtained by regressing Procrustes shape coordinates of each specimen on its centroid size expressed as a deviation from the mean centroid size of its species, and these residuals were used as size-corrected variables for PCA (see Kim et al., 2009 ; Zelditch et al., 2012 ; Klingenberg, 2016 ). Thin-plate spline (TPS) deformation grids included in the different figures depict shape variation between the mean configuration of specimens with positive scores and that of specimens with negative scores along each principal component (PC) and the reverse. Because pygidial morphology, which is critical for the systematics of Eodiscida, could not be incorporated into the landmark-based analysis, the results are interpreted as documenting cranidial shape differentiation within Hebediscus only. ChatGPT (OpenAI) was used to assist in debugging the R scripts used for the morphometric analyses; all analyses and interpretations were performed and verified by the authors. Results Principal Component 1 (PC1) explains 35.7% of the total Procrustes shape variance (Fig. 4 ). TPS deformation grids illustrate that shape variation along this axis is primarily associated with differences in the width (tr.) of the glabella relative to the cranidium, the width (tr.) of the frontal lobe, and the length (exsag.) of the palpebral lobes. Additional, comparatively minor contributions to the shape variation relate to differences in the length (exsag.) of the anterior facial sutures. Specimens with negative scores in PC1 are characterised by a wider (tr.) glabella, a wider (tr.) frontal lobe, shorter (exsag.) palpebral lobes, and longer (exsag.) anterior facial sutures. Conversely, specimens with positive scores exhibit a narrower (tr.) glabella, a narrower (tr.) frontal lobe, longer (exsag.) palpebral lobes, and shorter (exsag.) anterior facial sutures. In the latter region of morphospace in PC1, H . carlsi n. sp. is distinctly separated from the rest of species of Hebediscus , with specimens of H . vagus , H . lemdadensis , and one specimen of H . attleborensis from Siberia showing the greatest morphological similarity in the morphospace. The majority of species form relatively tight clusters along this axis. The main exception is H . attleborensis , as the specimens from Siberia, Morocco, and Newfoundland are notably distant from the specimen from Massachusetts. Notably, species from Newfoundland cluster tightly in the region of negative PC1 scores, with substantial overlap among species. PC2 explains 19.8% of the variance (Fig. 4 ) and also highlights the tight clustering of the species from Newfoundland, although with substantial overlap with the majority of the other species. However, the combined morphospace of the species from Newfoundland is clearly separated from that occupied by species from other regions when PC1 and PC2 are combined. Variation along PC2 mainly reflects differences in the width (tr.) of the frontal lobe and the length (exsag.) of the anterior facial sutures and palpebral lobes. Comparatively minor differences refer to the width (tr.) of the glabella and the length (sag.) of the preglabellar area. H . carlsi n. sp. overlaps in the morphospace with species from Newfoundland such H . williamsi , H . sp. 2, and the specimen assigned to H . attleborensis in PC2. In this region of the axis, the specimens are characterised by a wider (tr.) frontal lobe, longer (exsag.) anterior facial sutures, shorter (exsag.) palpebral lobes, and a slightly shorter (sag.) preglabellar area. In the opposite region of the morphospace, the specimen assigned to H . cf. lemdadensis is notably distant from the morphospace occupied by both H . lemdadensis and the remaining species of Hebediscus . As in PC1, specimens of H . attleborensis do not form a tight cluster, and the specimen from Massachusetts is notably distant from specimens from Morocco and Newfoundland. Although H . carlsi n. sp. forms a distinct cluster separated from the morphospace defined by the remaining species when PC1 and PC2 are combined (Fig. 4 ), their separation in morphospace from the main cluster of Hebediscus species is comparable with that of other species such as H . lemdadensis . As in PC2, the morphospace occupied by H . carlsi n. sp. exhibits a significant overlap with that of other species in PC3 (Fig. 5 ). This PC accounts for 14.5% of the total variance and is primarily associated with differences in the length (sag.) of the preglabellar area and the length (exsag.) of the palpebral lobes. The dispersion of the specimens of species such as H . planus , H . williamsi , H . vagus , and H . lemdadensis is notably wide, occupying regions associated with both positive and negative scores and indicating a wide intraspecific variability H . carlsi n. sp. is located in the region of morphospace characterised by longer (exsag.) palpebral lobes and a shorter (sag.) preglabellar area. In this region, this species overlaps with the morphospace of species such as H . planus , H . lemdadensis , and H . sp. indet A. The mean landmark configurations for the analysed species and forms are illustrated in Fig. 6 . H . carlsi n. sp. is clearly distinguished from other species of Hebediscus by landmarks 2, 3, and 4 (Fig. 3 ), which are positioned farther from the sagittal axis, indicating a relatively wide (tr.) cranidium compared to the glabella. This species is also characterised by a distinctly short (sag.) preglabellar area, reflected by the proximity of landmarks 1 and 7. The species from Newfoundland are separated from other taxa by their shorter (exsag.) palpebral lobes and wider (tr.) frontal lobe, consistent with their position in morphospace in Figs. 4 and 5 . The wide variability within the specimens currently assigned to H . attleborensis is also observable in Fig. 6 . The specimens from Massachusetts and Newfoundland exhibit markedly shorter (exsag.) palpebral lobes compared to the specimens from Siberia and Morocco, and the specimen from Massachusetts differ from that from Newfoundland by a longer (sag.) preglabellar area. Systematic Palaeontology Specimens from the Iberian Chains studied herein are housed in the Museo de Ciencias Naturales de la Universidad de Zaragoza, Spain, formerly the Museo Paleontológico de la Universidad de Zaragoza, under repository numbers MPZ 2021/366–369, and MPZ 2026/01–06. Specimens studied in this work were sampled under permission Reference Number 166/18-19-20-22-2025 from the Service of Prevention, Protection and Research of the Aragón Government. Class Trilobita Walch, 1771 Order Eodiscida Kobayashi, 1939 Superfamily Eodiscoidea Raymond, 1913 Family Hebediscidae Kobayashi, 1944 Genus Hebediscus Whitehouse, 1936 Type-species . Hebediscus attleborensis (Shaler and Foerste in Shaler, 1888 ), from the Brigus Formation (“Hoppin Slate”), Massachusetts (United States), by original designation, Cambrian Series 2. Discussion . Several cranidia recovered from the lower part of the Huérmeda Formation are notably reduced in size, with a length (sag.) ranging from slightly less than 1 mm to approximately 2 mm. The occurrence of several genera of the Redlichiida Richter, 1932 within the same stratigraphic interval suggests that these cranidia could represent juvenile individuals of one of those genera. However, their association with almost isopygous pygidia (see Fig. 7 a) instead indicates an affinity with the Eodiscida Kobayashi, 1939 . Among the families included within the Eodiscoidea Raymond, 1913 by Jell ( 1997 ), the specimens from the Huérmeda Formation exhibit greatest similarity to the Hebediscidae Kobayashi, 1944 . This interpretation is supported by their parallel-sided glabella lacking glabellar furrows and by a pygidial axis that is broad (tr.) anteriorly and tapers progressively posteriorly. The specimens also display some resemblance to members of the Calodiscidae Kobayashi, 1943 , particularly Neocobboldia Rasetti, 1952 and Korobovia Jell in Bengtson et al., 1990 . In these genera, however, the occipital furrow is relatively well defined, and in Neocobboldia the anterior border furrow is typically wider (tr.) than the anterior border. In contrast, the specimens from the Huérmeda Formation possess an anterior border that is wider (tr.) than the anterior border furrow and an occipital furrow that is weakly defined. A comparable morphology is observed in the yukoniid Hebediscina Rasetti, 1972 , although in that genus the glabella is distinctly narrower (tr.). The specimens discussed herein were tentatively assigned to Hebediscus Whitehouse, 1936 by Sepúlveda et al. ( 2022 ). Additional material recovered from the MT1 and M9 sections confirms that this taxon was well established in the lower part of the Huérmeda Formation of the Iberian Chains. A parallel-sided glabella with a subtruncate anterior margin and lacking glabellar furrows represents one of the principal diagnostic features observable in these generally poorly preserved specimens. Within the Hebediscidae, this morphology is more consistent with that of Hebediscus . The diagnosis of the genus provided by Jell ( 1997 ) includes several characters that cannot be assessed in the specimens from the Huérmeda Formation, such as a pygidium bearing seven or more axial rings. In the present specimens, as well as in Hebediscus planus (Hutchinson, 1962 ) and Hebediscus williamsi Westrop and Landing, 2011 , the number of axial rings is indeterminate. Geometric morphometric analysis indicates that the specimens from the Huérmeda Formation represent a distinct species of Hebediscus , characterised by a narrow (tr.) glabella in relation to the width (tr.) of the cranidium and by a short (sag.) preglabellar area. Their separation in morphospace is interpreted as intrageneric variation within Hebediscus rather than evidence for generic distinction, as the combination of qualitative characters observed in these specimens supports their assignment to Hebediscus rather than to a separate genus. The results further suggest a distinct cluster of cranidial morphologies among the Newfoundland material, including H . planus , H . williamsi , two forms left in open nomenclature by Westrop and Landing ( 2011 ), and a specimen assigned to Hebediscus attleborensis (Shaler and Foerste in Shaler, 1888 ) by Fletcher ( 1972 , 2006 ) and Fletcher and Theokritoff ( 2008 ), indicating a closer morphological affinity among these forms than with other species of the genus. Westrop and Landing ( 2011 ) argued that previous assignment of specimens from Newfoundland, Morocco and Siberia to H . attleborensis by different authors are unfounded. The results of the morphometric analysis presented here are consistent with this interpretation, given the pronounced separation in Procrustes morphospace between specimens of this species. Although Sepúlveda et al. ( 2022 ) considered the specimens from the Huérmeda Formation to represent the first record of the genus in the Iberian Chains, Clausen ( 2004 ) assigned several cranidia from the Valdemiedes Formation (upper Bilbilian) to juvenile individuals of the ellipsocephalid Alueva undulata Sdzuy, 1961 , which probably belong to Hebediscus (see Clausen, 2004 , Fig. 2.2–2.8). These specimens are, however, significantly younger than those from the Huérmeda Formation and other Hebediscus species, although they occupy a stratigraphic position comparable to that of various forms from Morocco tentatively assigned to the genus (see Geyer, 1988 ). Hebediscus carlsi n. sp. (Fig. 7 a–i) 2022 Hebediscus ? sp. – Sepúlveda et al., pp. 104–105, fig. 6A–D. 2024 Hebediscus ? sp. – Liñán et al., p. 725. 2024 Hebediscus ? sp. – Geyer, p. 355, fig. 132. 2025 Hebediscus ? sp. – Geyer and Landing, p. 25. Etymology . In tribute to Prof. Peter Carls, for his contribution to the knowledge of the geology and paleontology of the Palaeozoic of the Iberian Chains. Holotype . Internal mould of a cranidium (MPZ 2021/366) from the level 2 of the M9 section, lower part of the Huérmeda Formation (upper Marianian, Cambrian Series 2). Paratypes . Internal mould of two cranidia and one pygidium (MPZ 2021/367–369) the level 2 of the M9 section, lower part of the Huérmeda Formation (upper Marianian, Cambrian Series 2). Other material . Three cranidia and one pygidium (MPZ 2026/01–04) from the level 23 of the MT1 and level 2 of the M9 section, lower part of the Huérmeda Formation (upper Marianian, Cambrian Series 2). Diagnosis . A species of Hebediscus with a narrow (tr.) glabella with a subtruncate anterior margin; palpebral lobes moderately long (exsag.); preglabellar area short (sag.); anterior margin only slightly curved. Description . Cranidium subrectangular to subelliptical in outline; length (sag.) about 75% of cranidial width (tr.) across palpebral lobes. Glabella subrectangular and slightly tapering forward, moderately long (sag.), and convex with respect to the rest of the cranidium; length (sag.) about 75% of total cranidial length (sag.); sides faintly concave; width (tr.) at occipital lobe about 35% of cranidial width (tr.) across palpebral lobes; anterior margin flattened. Glabellar furrows obsolescent. Occipital furrow shallow. Occipital lobe relatively short (sag.), subsemicircular in outline, and curved backwards; length (sag.) about 12% of total cranidial length (sag.) and 15% of total glabellar length (sag.). Axial furrow deep and well-marked. Fixigena relatively wide (tr.) and slightly convex; width (tr.) across palpebral lobe about 80% of glabellar width (tr.) across palpebral lobe; moderately sloping up from axial furrow towards palpebral lobe, and sloping down posteriorly towards posterior border. Palpebral lobe moderately long (exsag.) and wide (tr.); length (exsag.) about 30% of total cranidial length (sag.); width (tr.) about 8% of cranidial width (tr.) across palpebral lobe. Eye ridge indistinct. Preocular area and preglabellar field deep and sloping down toward anterior border furrow. Anterior border furrow curved and moderately deep, subequal in depth than axial furrow.; slightly longer (sag.) in front of the glabella. Anterior border curved, convex, and relatively short (sag.); subequal in length all along. Anterior margin moderately curved. Posterior border convex in transverse profile. Pygidium subelliptical in outline and convex, with a prominent axis; length (sag.) about 75% of maximum pygidial width (tr.). Pygidial axis subconical and tapering posteriorly; length (sag.) about 85% of total pygidial length (sag.); width (tr.) anteriorly about 160% of pygidial axis width (tr.) posteriorly and about 40% of maximum pygidial width (tr.); posterior margin rounded and almost connected with pygidial border furrow; sides apparently straight. Axial furrow relatively shallow. Pleural field sloping up from lateral border to the axis. Pleural furrow not visible. Lateral and posterior border furrows moderately deep and well-marked all around. Lateral and posterior borders relatively narrow (tr. and sag.), convex, and subequal in length all around, very similar to anterior border of the cranidium. Posterior margin curved. Remarks . Geometric morphometric analysis of cranidial shape demonstrates that the specimens from the lower part of the Huérmeda Formation are clearly distinct from the majority of all previously described species of Hebediscus and can be regarded as representing a new species. These specimens differ from the rest of the species of the genus by a combination of a narrower (tr.) glabella with respect to the width (tr.) of the cranidium and, most notably, by a markedly short (sag.) preglabellar area. The reduced length (sag.) of the preglabellar area results in a less curved anterior cranidial margin, whereas in other species of the genus, such as those from Newfoundland and Siberia, the preglabellar area is conspicuously longer (sag.), and the anterior cranidial margin is distinctly curved or weakly pointed (see Korovnikov, 2007; Fletcher and Theokritoff, 2008; Westrop and Landing, 2011). Although the anterior border is short (sag.) in both the specimens from the Huérmeda Formation and other species of Hebediscus , the preglabellar field is distinctly shorter (sag.) in the former. A comparably reduced (sag.) preglabellar field is only known in various Moroccan specimens assigned to Hebediscus sp. indet. A and Hebediscus sp. indet. B by Geyer (1988, figs. 2, 3, 83, 84), the latter occurring at a similar stratigraphic position within the Sectigena Zone. These specimens also exhibit a narrow (tr.) glabella relative to the cranidium, closely resembling the specimens from the Huérmeda Formation. Conspecificity between Hebediscus sp. indet. B and the Spanish material is therefore plausible, although the poor preservation of the available pygidia of the latter prevents a detailed comparison with the distinctive pygidium of the Moroccan material. Other material showing a similar reduced (sag.) preglabellar area and a moderately curved anterior cranidial margin includes several specimens from Siberia previously assigned to H. attleborensis (see Repina, 1972, pl. 33, figs. 1, 2). However, Westrop and Landing (2011) argued that this species should be restricted to its type material from Massachusetts, and the Siberian specimens are therefore unlikely to belong to H. attleborensis . H . lemdadensis , another species with a comparable stratigraphic range from Morocco, also possesses a cranidium characterised by a relatively short (sag.) preglabellar area, although it appears slightly longer (sag.) than that of the specimens from the Huérmeda Formation. In addition, H . lemdadensis bears a distinct occipital spine, whereas the Spanish material lacks an occipital spine and shows a smooth posterior margin of the occipital lobe. Material from the Alconera Formation of the Ossa-Morena Zone, studied by Collantes (2023) and Collantes et al. (submitted) and assigned to Hebediscus , occupies a broadly similar stratigraphic position near the base of the upper Marianian. However, the poor preservation of this material prevents a confident comparison, and although the glabella appears narrow (tr.), the preglabellar area is proportionally longer (sag.) than in the specimens from the Huérmeda Formation. On the basis of the combination of cranidial characters and results of the morphometric analysis, Hebediscus carlsi n. sp. is proposed for the material from the lower part of the Huérmeda Formation. Family Yukoniidae S. Zhang in W. Zhang et al., 1980 Genus Hebediscina Rasetti, 1972 Type-species . Hebediscina sardoa Rasetti, 1972, from Matoppa Formation, Sardinia (Italy), by original designation, Cambrian Series 2. Hebediscina ? sp. (Figure 7j – o) Material and locality . Two cranidia preserved as internal moulds (MPZ 2026/05, 2026/06) from the level 23 of the MT1 section and level 3 of the M9 section, lower part of the Huérmeda Formation (upper Marianian, Cambrian Series 2). Other material studied . Two cranidia and two pygidia collected by Prof. Klaus Sdzuy in the level 23 of the lowermost Huérmeda Formation in the MT1 section in Tierga (according to the notes presented to Eladio Liñán and field data). These specimens are currently not available (Gerd Geyer, personal communication, 2021). Description and comparison . Two small cranidia recovered from the lower part of the Huérmeda Formation exhibit a markedly distinct morphology when compared with that of the co-occurring Hebediscus carlsi n. sp. These cranidia are characterised by an elongated (sag.) and notably narrow (tr.) glabella with a rounded anterior glabellar margin, attaining a width (tr.) of approximately 25% of the cranidial width (tr.) across the palpebral lobes. In H. carlsi n. sp., by contrast, the glabella reaches approximately 35% of the cranidial width (tr.) across the palpebral lobes, and the anterior glabellar margin is subtruncate. Additional differences include a longer (sag.) preglabellar area, comprising a longer (sag.) and distinctly depressed preglabellar field, the presence of well-defined preocular fields, and possibly longer (exsag.) palpebral lobes in the two cranidia discussed herein. Two pygidia collected by Prof. Klaus Sdzuy also differ from the pygidia associated with cranidia of H . carlsi n. sp. in having well-defined axial furrows to the sides, resulting in an axis with slightly indented sides. These features suggest that these specimens represent a distinct species and do not fit the typical morphology of Hebediscus . The distinctly narrow (tr.) glabella and the presence of well-developed preocular fields observed in these two cranidia suggest their tentative assignment to the Yukoniidae and, more specifically, to Hebediscina Rasetti, 1972. Comparable morphologies are also present in the calodiscid genera Neocobboldia and Korobovia . However, members of the Calodiscidae are characterised by a well-defined and complete occipital furrow, which is absent in the specimens from the Huérmeda Formation. In addition, Jell in Bengtson et al. (1990) listed the presence of a glabella without furrows as diagnostic for the genus, a condition which is also present in the specimens from the Huérmeda Formation. The prominent occipital spine that characterises the Yukoniidae, however, cannot be recognised in the present material. Furthermore, although the specimens are poorly preserved, the pygidium appears to possess up to three axial rings plus an articulating half-ring, whereas the diagnoses of Hebediscina and the Yukoniidae provided by Jell (1997) indicate the presence of four to seven axial rings. These discrepancies, in addition to the poor preservation of the material, prevent a confident generic assignment for the specimens from the Huérmeda Formation. Biostratigraphy and correlation Although Hebediscus exhibits a broad stratigraphic range in some regions, such as Morocco (see Geyer, 1988 ; Geyer and Landing, 2025 ) and Siberia (see Rozanov and Varlamov, 2008 ), the majority of species of the genus occur within a broadly comparable stratigraphic interval close to the boundary between Cambrian Stages 3 and 4 (see Geyer and Shergold, 2000 , table 1; Geyer, 2005 ). In the Iberian Peninsula, Hebediscus is consistently recorded from the base of the upper Marianian in both the Iberian Chains (see Sepúlveda et al., 2022 ; herein) and Ossa Morena Zone (see Collantes, 2023 ; Collantes et al., submitted). Along the West Gondwana margin, the genus is also present in the Sectigena Zone of Morocco (see Geyer, 1988 ; Geyer and Landing, 2025 ), which has been roughly correlated with the upper Marianian of Iberia (see Sundberg et al., 2016 ). In Morocco, however, Hebediscus has additionally been reported from older stratigraphic intervals, including the Antatlasia hollardi and Antatlasia gutta-pluviae zones, correlated with the lower and middle Marianian (see Sundberg et al., 2016 ), as well as from the younger Morocconus notabilis Zone, assigned to the Agdzian Stage (see Geyer, 1988 ; Geyer and Landing, 2025 ). In Avalonia, the type species of the genus comes from the Hebediscus attleborensis Subzone (uppermost Callavia broeggeri Zone) of the Branchian Series in Massachusetts (see Shaw, 1950 ; Landing, 1988 ; Fletcher and Theokritoff, 2008 ), which is generally correlated with the upper part of Stage 3 or the lower part of Stage 4 of the Cambrian (see Sundberg et al. 2016 ; Geyer, 2019 ). Hebediscus is also abundant in Newfoundland, where it also occurs in the uppermost Callavia broeggeri Zone (see Hutchinson, 1962 ; Fletcher, 1972 , 2006 ; Westrop and Landing, 2011 ). In Eastern Avalonia, the genus has been reported from a comparable stratigraphic position within the Callavia Zone in the Comley Quarry, England (see Cobbold, 1931 ; Rushton et al., 1999 ; Rushton, 2025 ). In Siberia and Central Asian Orogenic Belt ( sensu Zonenshain et al., 1990 ), the stratigraphic range of Hebediscus appears to be broader than in Avalonia (Astashkin et al., 1991 , 1995 ). The genus has been recorded from the Bergeroniellus micmacciformis - Erbiella Zone (see Rozanov and Varlamov, 2008 ), within the lower Botoman stage, which has been correlated with the lower Stage 4 of the Cambrian (see Geyer, 2019 ). Rozanov and Varlamov ( 2008 ) also reported the occurrence of the genus in the Bergerioniaspis ornata Zone, of a younger age in the upper Botoman stage (see Geyer, 2019 ), and Korovnikov ( 2007 ) and Korovnikov and Novozhilova ( 2012 ) indicated its occurrence in the Judomia mattajensis - Uktaspis granulata Zone, upper Atdabanian, slightly below the proposed boundary between Cambrian Stages 3 and 4 (see Geyer, 2019 ). Finally, Rasetti ( 1967 ) defined Hebediscus marginatus from the Elliptocephala asaphoides fauna in the Taconic Allochthon. This species is recorded together with Serrodiscus speciosus (Ford, 1873 ) in a level that has been correlated with the upper Marianian (Collantes et al., 2022 ). The stratigraphic position of this species would be equivalent to that of Hebediscus carlsi . However, Fritz ( 1973 ) assigned H . marginatus to Ekwipagetia Fritz, 1973 . The geographic distribution of Hebediscina is more restricted than that of Hebediscus . The type material of Hebediscina derives from the Matoppa Formation of Sardinia (see Rasetti, 1972 ), which has an older age and has been correlated with the Ovetian stage (Pillola, 1991 ; Pillola et al. 1995 ), a similar age to that of the occurrence of the genus in South China (see Lin, 2008 ; Zhang and Clarkson, 2012 ). In contrast, in Australia the genus occurs in the Pararaia janeae Zone (see Bengtson et al., 1990 ), which is correlated with the lower Stage 4 of the Cambrian (see Geyer, 2019 ; Laurie et al., 2024 ). Despite local extensions into older and younger intervals, Hebediscus and Hebediscina are characteristic of the interval surrounding the boundary between Cambrian Stages 3 and 4. Several authors have emphasised the potential of Hebediscus attleborensis , together with Calodiscus , Serrodiscus , and Triangulaspis (known as the “HCST band”), for the intercontinental correlation of this boundary (see Geyer and Shergold, 2000 ; Geyer, 2005 ). However, the assignment of H. attleborensis outside its type area in Massachusetts has been widely questioned (see Westrop and Landing, 2011 ). This topic was also recently discussed by Geyer and Landing ( 2025 ), who referred to the Moroccan material previously assigned to H. attleborensis by Hupé ( 1953 ) as Hebediscus new species 1. The morphometric results presented herein further support the interpretation that specimens from Morocco, Siberia, and Newfoundland previously assigned to H. attleborensis represent taxa distinct from the Massachusetts type material. Nevertheless, the generic occurrence of Hebediscus remains a useful biostratigraphic indicator for approximating the lower boundary of Cambrian Stage 4 across several palaeocontinents, including the lower part of the Huérmeda Formation in the Iberian Chains. The presence of Hebediscina additionally provides a tentative correlation with the Pararaia janeae Zone of Australia, where Hebediscus has not been recorded. In this region, Hebediscina occurs in association with Serrodiscus (Bengtson et al., 1990 ), a taxon also present at the base of the upper Marianian in the Ossa Morena and Central Iberian zones (see Collantes et al., 2022 ; Sepúlveda et al., 2024 ). Figure 8 summarises the paleogeographic distribution of both genera according to the early Cambrian palaeogeographic reconstruction of Pillola ( 1990 ) and McKerrow et al. ( 1992 ). Hebediscina is distributed in the redlichiid realm and the intermediate bigotinid realm, whereas Hebediscus is present in the intermediate bigotinid realm and Avalonia. Conclusions New material recovered from the lower part of the Huérmeda Formation (upper Marianian, Cambrian Series 2) documents the presence of Eodiscida in the Iberian Chains. Landmark-based morphometric analysis of cranidial shape of specimens previously tentatively assigned to Hebediscus , in conjunction with qualitative morphological observations, demonstrates that the material from the Huérmeda Formation represents a distinct species, herein described as Hebediscus carlsi n. sp. This species is characterised by a relatively narrow (tr.) glabella and a markedly short (sag.) preglabellar area, resulting in a less curved anterior cranidial margin. Specimens from the same stratigraphic horizon displaying distinct cranidial morphology are tentatively assigned to Hebediscina , constituting the first record of this genus in the Iberian Peninsula. Results of the morphometric analysis support previous suggestions that several specimens assigned to Hebediscus attleborensis outside its type area in Massachusetts do not belong to that species, reinforcing the view that H. attleborensis is unsuitable as a precise intercontinental index taxon. Nevertheless, the generic occurrence of Hebediscus , in association with other taxa, remains a valuable tool for broad correlation of the interval around the Cambrian Stage 3–4 boundary. The co-occurrence of Hebediscus and Hebediscina in the lower part of the Huérmeda Formation strengthens correlations between the Iberian Chains, the Ossa-Morena Zone, Morocco, Avalonia, Siberia, Central Asian Orogenic Belt, and Australia, and highlights the importance of Eodiscida for refining regional and intercontinental correlations within Cambrian Series 2. Declarations Acknowledgements . This is a contribution to the GIUV2017-395 Research Group of the Universitat de València and to the project IGCPs 652 “Reading geologic time in Palaeozoic sedimentary rocks”. We are grateful to Ms. Isabel Pérez Urresti (technician of the University of Zaragoza) who assisted us with the photography. Author contributions . Conceptualization: Alexandre Sepúlveda, Rodolfo Gozalo; Methodology: Alexandre Sepúlveda; Formal analysis and investigation: Alexandre Sepúlveda; Writing - original draft preparation: Alexandre Sepúlveda; Writing - review and editing: Alexandre Sepúlveda, Rodolfo Gozalo, Eladio Liñán, Juan B. Chirivella-Martorell; Data curation: Alexandre Sepúlveda, Rodolfo Gozalo, Eladio Liñán, Juan B. Chirivella-Martorell; Visualization: Alexandre Sepúlveda, Rodolfo Gozalo. Funding . This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Data Availability . The list of specimens included in the geometric morphometric analyses (catalogue numbers and source publications for images) is provided in Supplementary Information 1. Landmark coordinate data and analysis scripts are not publicly available. Competing Interests The authors declare no competing interests. References Adams, D. C., & Otárola-Castillo, E. 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09:52:38","extension":"png","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":252182,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFig6.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/207851942491bed2b33ce057.png"},{"id":101751324,"identity":"1e901e5f-6344-4468-9162-a68a44e08fa4","added_by":"auto","created_at":"2026-02-03 10:19:19","extension":"png","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":40858953,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFig7.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/56b579b5ee407c34a02e862f.png"},{"id":101202981,"identity":"4dbbc8c3-aa19-4458-81ff-89e394a9be12","added_by":"auto","created_at":"2026-01-27 09:38:23","extension":"png","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":2172160,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFig8.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/a599431b57915aa3da727159.png"},{"id":100969374,"identity":"6bf7071f-bd83-41de-8941-28c795ba5660","added_by":"auto","created_at":"2026-01-23 09:52:38","extension":"xml","order_by":30,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":204048,"visible":true,"origin":"","legend":"","description":"","filename":"PBPED26000120structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/7ce11587913a1590c2e9e93e.xml"},{"id":100969377,"identity":"e2fb2644-bb10-4731-a4e7-8b9ed6b1659e","added_by":"auto","created_at":"2026-01-23 09:52:38","extension":"html","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":224296,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/d80d786d362db4b5d56fff3e.html"},{"id":100969351,"identity":"521f335b-c113-48d3-93b0-0f6c20414d71","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":19894090,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Map of the Iberian Peninsula showing pre-Hercynian outcrop areas. (b) Location of the studied sections in the Iberian Chains; modified from Gozalo and Liñán (1988). SPZ, South Portuguese Zone; OMZ, Ossa-Morena Zone; CIZ, Central Iberian Zone; WALZ, West Asturian-Leonese Zone; CZ, Cantabrian Zone; DM, Demanda Mountains; IC, Iberian Chains; PY, Pyrenees; CCR, Catalan Coastal Range; BC, Betic Chain. 1, Minas-Tierga 1 section (Tierga); 2, Mesones-9 section (Mesones de Isuela).\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/c9e228f766914c871e871ec2.png"},{"id":100969348,"identity":"6e40440e-0c7a-4723-ae4b-e76dfbc29a07","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":11679874,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic logs of the MT1 and M9 sections and distribution of the studied taxa. Modified from Sepúlveda et al. (2022). Fm., Formation; ISCS, International Subcommission on Cambrian Stratigraphy.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/7ebdd7da176e2571e534399a.png"},{"id":101202712,"identity":"90c07870-8a6e-4fc1-8173-f9c1f70d1d6c","added_by":"auto","created_at":"2026-01-27 09:37:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":17365620,"visible":true,"origin":"","legend":"\u003cp\u003eLandmarks (red dots) chosen for the morphometric analysis of the \u003cem\u003eHebediscus\u003c/em\u003e species. 1, intersection of anterior cranidial margin and sagittal axis; 2, distal lateral point of the frontal area; 3, anterior tip of the palpebral lobe; 4, posterior tip of the palpebral lobe; 5, intersection of posterior margin of occipital lobe and posterior margin of posterior border; 6, intersection of posterior margin of occipital lobe and sagittal axis; 7, intersection of anterior glabellar margin and sagittal axis; 8, intersection of glabellar margin and ocular ridge.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/e9ddd4ce28817e202857d44d.png"},{"id":101204231,"identity":"1ead2823-8e59-4d57-8530-db4674675347","added_by":"auto","created_at":"2026-01-27 09:42:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":23579720,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the specimens of the different species regarding PC1 (35.7% of the variance) and PC2 (19.8% of the variance) in the PCA of the landmarks. Filled shapes correspond to species or forms from Newfoundland. Thin-plate splines show shape variation of the mean configuration of the specimens with positive values towards that of the specimens with negative values for each axis, and the reverse.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/9c4bbdb482a54e08c536fd15.png"},{"id":100969355,"identity":"ef7192a1-8eb6-4744-aeb8-16c7161d46e7","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":23547012,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the specimens of the different species regarding PC1 (35.7% of the variance) and PC3 (14.5% of the variance) in the PCA of the landmarks. Filled shapes correspond to species or forms from Newfoundland. Thin-plate splines show shape variation of the mean configuration of the specimens with positive values towards that of the specimens with negative values for each axis, and the reverse.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/ece6622be2477f807cb00c7b.png"},{"id":100969360,"identity":"23db1204-1c81-47dc-9ccd-c40c61fa7600","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":9952466,"visible":true,"origin":"","legend":"\u003cp\u003eMean landmark configuration of each species. Each configuration has been anchored at landmark 6, corresponding to the intersection of the sagittal axis and the posterior margin of occipital lobe (see Fig. 3). X and Y axes have been flipped to match the original position of landmarks.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/c1e782922bb5ec7425ee5f51.png"},{"id":100969349,"identity":"49dca336-ae48-4fc3-aa1f-9e1876f4429d","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1600415,"visible":true,"origin":"","legend":"\u003cp\u003ea–i, \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp., a, small slab containing MPZ 2021/366–369; level 2 of the M9 section. b, internal mould of a cranidium. MPZ 2021/366. Holotype. c, internal mould of a cranidium. MPZ 2021/367. d, internal mould of a cranidium. MPZ 2021/368. e, internal mould of a cranidium. MPZ 2026/02; level 23 of the MT1 section. f, internal mould of a cranidium. MPZ 2026/03; level 23 of the MT1 section. g, internal mould of a cranidium. MPZ 2026/01; level 23 of the MT1 section. h, internal mould of a pygidium. MPZ 2021/369; level 2 of the M9 section. i, internal mould of a pygidium. MPZ 2026/04; level 2 of the M9 section. j–o, \u003cem\u003eHebediscina\u003c/em\u003e? sp. j, internal mould of a cranidium. Level 23 of the MT1 section. k, internal mould of a cranidium. MPZ 2026/05; level 3 of the M9 section. l, internal mould of a cranidium. MPZ 2026/06; level 23 of the MT1 section. m, internal mould of a cranidium. Level 23 of the MT1 section. n, internal mould of a cranidium. Level 23 of the MT1 section. o, internal mould of a cranidium. Level 23 of the MT1 section. Specimens in j, m–o currently not available (Gerd Geyer, 2021, personal communication). Scale bars represent: 0.5 mm (d-g, i), 1 mm (a–c, h, j–o).\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/f30f56bb6292e5a9e874c227.png"},{"id":101202798,"identity":"80d654d5-8b5c-43b3-9865-44531d3cc5e4","added_by":"auto","created_at":"2026-01-27 09:37:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":30889986,"visible":true,"origin":"","legend":"\u003cp\u003eEarly Cambrian continental reconstruction showing occurrences of \u003cem\u003eHebediscus\u003c/em\u003e and \u003cem\u003eHebediscina\u003c/em\u003e. Modified from Pillola (1990) and McKerrow et al. (1992). Box marks the occurrence of \u003cem\u003eHebediscus\u003c/em\u003e and \u003cem\u003eHebediscina\u003c/em\u003e in the Iberian Chains.\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/d8e41dee6bbcbd8a54203321.png"},{"id":100969346,"identity":"e96bf3c3-cc2c-420b-9c02-e1a404f4232e","added_by":"auto","created_at":"2026-01-23 09:52:37","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":15376,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Information 1. Specimens included in the morphometric analysis.\u003c/p\u003e","description":"","filename":"SupplementaryInformation1.docx","url":"https://assets-eu.researchsquare.com/files/rs-8653291/v1/3978efb06d6559b0f39c20e6.docx"}],"financialInterests":"","formattedTitle":"Presence of Eodiscida (Trilobita) in the Cambrian Series 2 of the Iberian Chains (Northeast Spain)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe strong endemism of Cambrian Series 2 trilobite faunas, and the resulting lack of intercontinental faunal connections, has hindered the formal ratification of this series and of Stages 3 and 4 of the Cambrian. These correlation difficulties have also affected the correlation of the regional stages of the Iberian Peninsula for this interval, traditionally including the Ovetian, Marianian and Bilbilian stages (Sdzuy, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1993\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Shergold, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Gozalo et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Sundberg et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Peng et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, the markers used to define the boundaries between these stages have been revised repeatedly (Sdzuy, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n and G\u0026aacute;mez-Vintaned, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1993\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1996\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). In recent years, several authors have been working on the establishment of more robust correlations across the Iberian Peninsula, especially in the Marianian stage (Collantes et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the Iberian Chains (Northeast Spain), one of the regions of the Iberian Peninsula with extensive Cambrian outcrops, the Marianian deposits are comprised in the Ribota and Hu\u0026eacute;rmeda formations. Compared with other Cambrian intervals in this area, the trilobite fauna from this stratigraphic interval has remained relatively poorly studied, and only a limited number of works have addressed its systematics and biostratigraphy (Richter and Richter, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1948\u003c/span\u003e; Sdzuy, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e1961\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2025\u003c/span\u003e in press; \u0026Aacute;lvaro et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Collantes et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). One of the most characteristic fossiliferous horizons within this interval occurs at the lower part of the Hu\u0026eacute;rmeda Formation (see Lotze, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1961\u003c/span\u003e; Sdzuy, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e1961\u003c/span\u003e), which has been correlated with the base of the upper Marianian. Trilobites from this horizon have recently been the focus of several detailed systematic studies (see Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2025\u003c/span\u003e in press; \u0026Aacute;lvaro et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Collantes et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, most of the taxa studied in these works have relatively limited potential for regional and intercontinental correlation\u003c/p\u003e \u003cp\u003eThe present study addresses the occurrence of the globally distributed Eodiscida Kobayashi, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1939\u003c/span\u003e in the lower part of the Hu\u0026eacute;rmeda Formation. Morphometric analyses of the cranidial morphology of specimens tentatively assigned to \u003cem\u003eHebediscus\u003c/em\u003e Whitehouse, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1936\u003c/span\u003e by Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), together with newly collected material and data from species of the genus from other regions, indicate that these specimens represent a distinct species, \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. The new species is characterised by a narrow (tr.) glabella with a subtruncate anterior glabellar margin, a short (sag.) preglabellar area, and a slightly curved anterior cranidial margin. Additional specimens from the same stratigraphic horizon display a different morphology and are tentatively assigned to the closely related genus \u003cem\u003eHebediscina\u003c/em\u003e Rasetti, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, representing the first record of this genus in the Iberian Peninsula. \u003cem\u003eHebediscus\u003c/em\u003e has long been regarded as a key taxon for intercontinental correlation of the base of Cambrian Stage 4 (Geyer and Shergold, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Geyer, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Sundberg et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), with the majority of species occurring near this level across several palaeocontinents, including West Gondwana, Avalonia, Siberia, and Central Asian Orogenic Belt. The genus also provides an important correlation tool along the West Gondwana margin, having been reported from comparable stratigraphic positions in the Ossa-Morena area of the Iberian Peninsula and the \u003cem\u003eSectigena\u003c/em\u003e Zone of Morocco. Furthermore, \u003cem\u003eHebediscina\u003c/em\u003e has been recorded from a horizon equivalent to the lower part of the Hu\u0026eacute;rmeda Formation in Australia.\u003c/p\u003e"},{"header":"Geological and stratigraphic setting","content":"\u003cp\u003eThe material studied herein comes from the municipalities of Tierga and Mesones de Isuela, located in the northern sector of the Iberian Chains (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), one of the areas of the Iberian Peninsula with extensive exposure of Palaeozoic rocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The Iberian Chains consists of two northwest-southwest parallel strings separated by the Tertiary Calatayud basin and form part of the Cantabrian and West-Asturian Leonese zones of the Iberian Peninsula (Gozalo and Li\u0026ntilde;\u0026aacute;n, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The Iberian Chains are divided into the Badules, Mesones, and Herrera tectonostratigraphic units by the Jarque and Datos faults. The Cambrian Series 2 lithostratigraphic sequence of the Iberian Chains comprises, in ascending order, the B\u0026aacute;mbola, Embid, Jal\u0026oacute;n, Ribota, Hu\u0026eacute;rmeda, Daroca, and Valdemiedes formations (see Lotze, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1961\u003c/span\u003e; Schmidt-Thom\u0026eacute;, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Li\u0026ntilde;\u0026aacute;n et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1996\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Gozalo et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe specimens examined in this study were collected from the lower part of the Hu\u0026eacute;rmeda Formation, in the level 23 of the Minas Tierga-1 (MT1) section, and levels 2 and 3 of the Mesones-9 (M9) section (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e2\u003c/span\u003e), both located within the Mesones Unit. The stratigraphy of the MT1 section and the systematics of part of its trilobite fauna were presented by Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), with additional research provided by Collantes et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2025\u003c/span\u003e in press). Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) also documented the stratigraphy of the M9 section and studied its trilobite fauna. The systematics of several species from this horizon from nearby sections was also examined by \u0026Aacute;lvaro et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Hu\u0026eacute;rmeda Formation consists of a succession of green to dark blue shales, weathering to brown or blackish colours, and minor intercalations of yellow dolostone, marl, and sandstone. The base of this formation is readily identified above the upper massive dolostone bank of the Ribota Formation. The transition between the two formations is gradual, as thin dolostone beds occur in the lower part of the Hu\u0026eacute;rmeda Formation in various sections and areas (see Scheuplein, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Aliaga, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1968\u003c/span\u003e; Schmidt-Thom\u0026eacute;, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e1968\u003c/span\u003e, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Schmitz, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). The fine-grained detrital sediments of the Hu\u0026eacute;rmeda Formation have been interpreted as having been deposited in an open-shelf sublittoral environment (G\u0026aacute;mez et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; \u0026Aacute;lvaro et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). The trilobite-bearing shale facies in the lower part of this formation are indicative of more open marine conditions (\u0026Aacute;lvaro et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1995\u003c/span\u003e), which are also reflected in the wide geographical distribution of several taxa recorded from this horizon (see Sdzuy, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e1961\u003c/span\u003e, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; \u0026Aacute;lvaro et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; herein).\u003c/p\u003e"},{"header":"Morphometric analysis","content":"\u003cp\u003eA landmark-based geometric morphometric analysis was conducted to assess the cranidial shape affinities between specimens of \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. from the lower part of the Hu\u0026eacute;rmeda Formation and species of the genus from other regions. The dataset comprises 46 specimens representing several species, including \u003cem\u003eH\u003c/em\u003e. \u003cem\u003egranulosus\u003c/em\u003e Lazarenko, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e1962\u003c/span\u003e, H. \u003cem\u003esublongus\u003c/em\u003e Korovnikov, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2007\u003c/span\u003ed \u003cem\u003evagus\u003c/em\u003e Egorova in Egorova and Savitskiy, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1969\u003c/span\u003e from Siberia; \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e from Morocco; \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eplanus\u003c/em\u003e (Hutchinson, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1962\u003c/span\u003e) and \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ewilliamsi\u003c/em\u003e Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e from Newfoundland; multiple specimens assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e (Shaler and Foerste in Shaler, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1888\u003c/span\u003e) from Massachusetts, Morocco, Newfoundland, and Siberia (see Shaw, \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e1950\u003c/span\u003e; Hup\u0026eacute;, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1953\u003c/span\u003e; Egorova and Savitskiy, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Fletcher, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Fletcher and Theokritoff, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Rozanov and Varlamov, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2008\u003c/span\u003e); and \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. from the Hu\u0026eacute;rmeda Formation. Several specimens of forms referred to \u003cem\u003eHebediscus\u003c/em\u003e in open nomenclature were also included, such as \u003cem\u003eH\u003c/em\u003e. sp. 1 and \u003cem\u003eH\u003c/em\u003e. sp. 2 from Newfoundland (see Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), and \u003cem\u003eH\u003c/em\u003e. sp. indet. A and \u003cem\u003eH\u003c/em\u003e. cf. \u003cem\u003elemdadensis\u003c/em\u003e from Morocco (see Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The latter was subsequently reassigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e by Geyer (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The geographic origin of specimens assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e was controlled in order to evaluate the proposal that only the type material from Massachusetts should be retained within the species (see Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Geyer and Landing, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). It should be noted that the specimen from Newfoundland assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e by Fletcher (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) and Fletcher and Theokritoff (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) was subsequently reassigned to \u003cem\u003eH\u003c/em\u003e. sp. 1 by Westrop and Landing (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSeveral species assigned to \u003cem\u003eHebediscus\u003c/em\u003e, such as \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elermontovae\u003c/em\u003e Repina, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1960\u003c/span\u003e, H. \u003cem\u003eerbaensis\u003c/em\u003e Repina in Repina et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1964\u003c/span\u003e, H. \u003cem\u003eflexus\u003c/em\u003e Repina in Repina et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1964\u003c/span\u003e, H. \u003cem\u003epokrovskayae\u003c/em\u003e Zadorozhnaya in Zhuravleva et al., \u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e1967\u003c/span\u003e, H. \u003cem\u003econvexus\u003c/em\u003e Nikiforov in Repina et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e1974\u003c/span\u003e, H. \u003cem\u003edurus\u003c/em\u003e Korobov, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1980\u003c/span\u003e, as well as \u003cem\u003eH\u003c/em\u003e. sp. indet. B \u003cem\u003esensu\u003c/em\u003e Geyer (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) and specimens assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e by Repina (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e1972\u003c/span\u003e), were excluded from the analysis due to the poor preservation of the available cranidia. Details of specimen catalogue numbers and source publications for the images used in landmarking are provided in Supplementary Information 1 (SI1).\u003c/p\u003e \u003cp\u003eEight homologous anatomical landmarks (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3\u003c/span\u003e) were digitised on the available cranidia using TpsDig (Rohlf, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Prior to landmarking, images of specimens exhibiting oblique tectonic deformation were digitally retrodeformed using Adobe Photoshop. Specimens displaying strong sagittal or transverse compression were excluded from the analysis. Landmark coordinates were imported into the R environment (v. 4.3.2; R Core Team \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and analysed using the geomorph package (Adams and Ot\u0026aacute;rola-Castillo, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Landmarks were placed on the right side of the cranidia when possible; specimens landmarked on the left side were computationally mirrored prior to the analysis. Following Generalised Procrustes Alignment (GPA), a Principal Component Analysis (PCA) was performed on size-corrected Procrustes shape coordinates. Because a Procrustes regression of shape on centroid size revealed a significant heterogeneity of allometric slopes among species (logCS x species: F\u0026thinsp;=\u0026thinsp;2.1079, p\u0026thinsp;=\u0026thinsp;0.011), residuals were obtained by regressing Procrustes shape coordinates of each specimen on its centroid size expressed as a deviation from the mean centroid size of its species, and these residuals were used as size-corrected variables for PCA (see Kim et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zelditch et al., \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Klingenberg, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Thin-plate spline (TPS) deformation grids included in the different figures depict shape variation between the mean configuration of specimens with positive scores and that of specimens with negative scores along each principal component (PC) and the reverse. Because pygidial morphology, which is critical for the systematics of Eodiscida, could not be incorporated into the landmark-based analysis, the results are interpreted as documenting cranidial shape differentiation within \u003cem\u003eHebediscus\u003c/em\u003e only. ChatGPT (OpenAI) was used to assist in debugging the R scripts used for the morphometric analyses; all analyses and interpretations were performed and verified by the authors.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003ePrincipal Component 1 (PC1) explains 35.7% of the total Procrustes shape variance (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e). TPS deformation grids illustrate that shape variation along this axis is primarily associated with differences in the width (tr.) of the glabella relative to the cranidium, the width (tr.) of the frontal lobe, and the length (exsag.) of the palpebral lobes. Additional, comparatively minor contributions to the shape variation relate to differences in the length (exsag.) of the anterior facial sutures. Specimens with negative scores in PC1 are characterised by a wider (tr.) glabella, a wider (tr.) frontal lobe, shorter (exsag.) palpebral lobes, and longer (exsag.) anterior facial sutures. Conversely, specimens with positive scores exhibit a narrower (tr.) glabella, a narrower (tr.) frontal lobe, longer (exsag.) palpebral lobes, and shorter (exsag.) anterior facial sutures. In the latter region of morphospace in PC1, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. is distinctly separated from the rest of species of \u003cem\u003eHebediscus\u003c/em\u003e, with specimens of \u003cem\u003eH\u003c/em\u003e. \u003cem\u003evagus\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e, and one specimen of \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e from Siberia showing the greatest morphological similarity in the morphospace. The majority of species form relatively tight clusters along this axis. The main exception is \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e, as the specimens from Siberia, Morocco, and Newfoundland are notably distant from the specimen from Massachusetts. Notably, species from Newfoundland cluster tightly in the region of negative PC1 scores, with substantial overlap among species.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePC2 explains 19.8% of the variance (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and also highlights the tight clustering of the species from Newfoundland, although with substantial overlap with the majority of the other species. However, the combined morphospace of the species from Newfoundland is clearly separated from that occupied by species from other regions when PC1 and PC2 are combined. Variation along PC2 mainly reflects differences in the width (tr.) of the frontal lobe and the length (exsag.) of the anterior facial sutures and palpebral lobes. Comparatively minor differences refer to the width (tr.) of the glabella and the length (sag.) of the preglabellar area. \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. overlaps in the morphospace with species from Newfoundland such \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ewilliamsi\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. sp. 2, and the specimen assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e in PC2. In this region of the axis, the specimens are characterised by a wider (tr.) frontal lobe, longer (exsag.) anterior facial sutures, shorter (exsag.) palpebral lobes, and a slightly shorter (sag.) preglabellar area. In the opposite region of the morphospace, the specimen assigned to \u003cem\u003eH\u003c/em\u003e. cf. \u003cem\u003elemdadensis\u003c/em\u003e is notably distant from the morphospace occupied by both \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e and the remaining species of \u003cem\u003eHebediscus\u003c/em\u003e. As in PC1, specimens of \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e do not form a tight cluster, and the specimen from Massachusetts is notably distant from specimens from Morocco and Newfoundland. Although \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. forms a distinct cluster separated from the morphospace defined by the remaining species when PC1 and PC2 are combined (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e), their separation in morphospace from the main cluster of \u003cem\u003eHebediscus\u003c/em\u003e species is comparable with that of other species such as \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eAs in PC2, the morphospace occupied by \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. exhibits a significant overlap with that of other species in PC3 (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This PC accounts for 14.5% of the total variance and is primarily associated with differences in the length (sag.) of the preglabellar area and the length (exsag.) of the palpebral lobes. The dispersion of the specimens of species such as \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eplanus\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ewilliamsi\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003evagus\u003c/em\u003e, and \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e is notably wide, occupying regions associated with both positive and negative scores and indicating a wide intraspecific variability \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. is located in the region of morphospace characterised by longer (exsag.) palpebral lobes and a shorter (sag.) preglabellar area. In this region, this species overlaps with the morphospace of species such as \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eplanus\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e, and \u003cem\u003eH\u003c/em\u003e. sp. indet A.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe mean landmark configurations for the analysed species and forms are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e6\u003c/span\u003e. \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ecarlsi\u003c/em\u003e n. sp. is clearly distinguished from other species of \u003cem\u003eHebediscus\u003c/em\u003e by landmarks 2, 3, and 4 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e3\u003c/span\u003e), which are positioned farther from the sagittal axis, indicating a relatively wide (tr.) cranidium compared to the glabella. This species is also characterised by a distinctly short (sag.) preglabellar area, reflected by the proximity of landmarks 1 and 7. The species from Newfoundland are separated from other taxa by their shorter (exsag.) palpebral lobes and wider (tr.) frontal lobe, consistent with their position in morphospace in Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The wide variability within the specimens currently assigned to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e is also observable in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The specimens from Massachusetts and Newfoundland exhibit markedly shorter (exsag.) palpebral lobes compared to the specimens from Siberia and Morocco, and the specimen from Massachusetts differ from that from Newfoundland by a longer (sag.) preglabellar area.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Systematic Palaeontology","content":"\u003cp\u003eSpecimens from the Iberian Chains studied herein are housed in the Museo de Ciencias Naturales de la Universidad de Zaragoza, Spain, formerly the Museo Paleontol\u0026oacute;gico de la Universidad de Zaragoza, under repository numbers MPZ 2021/366\u0026ndash;369, and MPZ 2026/01\u0026ndash;06. Specimens studied in this work were sampled under permission Reference Number 166/18-19-20-22-2025 from the Service of Prevention, Protection and Research of the Arag\u0026oacute;n Government.\u003c/p\u003e \u003cp\u003eClass Trilobita Walch, \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e1771\u003c/span\u003e\u003c/p\u003e \u003cp\u003eOrder Eodiscida Kobayashi, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1939\u003c/span\u003e\u003c/p\u003e \u003cp\u003eSuperfamily Eodiscoidea Raymond, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1913\u003c/span\u003e\u003c/p\u003e \u003cp\u003eFamily Hebediscidae Kobayashi, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1944\u003c/span\u003e\u003c/p\u003e \u003cp\u003eGenus \u003cem\u003eHebediscus\u003c/em\u003e Whitehouse, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1936\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eType-species\u003c/b\u003e. \u003cem\u003eHebediscus attleborensis\u003c/em\u003e (Shaler and Foerste in Shaler, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1888\u003c/span\u003e), from the Brigus Formation (\u0026ldquo;Hoppin Slate\u0026rdquo;), Massachusetts (United States), by original designation, Cambrian Series 2.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDiscussion\u003c/b\u003e. Several cranidia recovered from the lower part of the Hu\u0026eacute;rmeda Formation are notably reduced in size, with a length (sag.) ranging from slightly less than 1 mm to approximately 2 mm. The occurrence of several genera of the Redlichiida Richter, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e1932\u003c/span\u003e within the same stratigraphic interval suggests that these cranidia could represent juvenile individuals of one of those genera. However, their association with almost isopygous pygidia (see Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) instead indicates an affinity with the Eodiscida Kobayashi, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1939\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong the families included within the Eodiscoidea Raymond, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1913\u003c/span\u003e by Jell (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), the specimens from the Hu\u0026eacute;rmeda Formation exhibit greatest similarity to the Hebediscidae Kobayashi, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1944\u003c/span\u003e. This interpretation is supported by their parallel-sided glabella lacking glabellar furrows and by a pygidial axis that is broad (tr.) anteriorly and tapers progressively posteriorly. The specimens also display some resemblance to members of the Calodiscidae Kobayashi, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1943\u003c/span\u003e, particularly \u003cem\u003eNeocobboldia\u003c/em\u003e Rasetti, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1952\u003c/span\u003e and \u003cem\u003eKorobovia\u003c/em\u003e Jell in Bengtson et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e. In these genera, however, the occipital furrow is relatively well defined, and in \u003cem\u003eNeocobboldia\u003c/em\u003e the anterior border furrow is typically wider (tr.) than the anterior border. In contrast, the specimens from the Hu\u0026eacute;rmeda Formation possess an anterior border that is wider (tr.) than the anterior border furrow and an occipital furrow that is weakly defined. A comparable morphology is observed in the yukoniid \u003cem\u003eHebediscina\u003c/em\u003e Rasetti, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, although in that genus the glabella is distinctly narrower (tr.).\u003c/p\u003e \u003cp\u003eThe specimens discussed herein were tentatively assigned to \u003cem\u003eHebediscus\u003c/em\u003e Whitehouse, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1936\u003c/span\u003e by Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Additional material recovered from the MT1 and M9 sections confirms that this taxon was well established in the lower part of the Hu\u0026eacute;rmeda Formation of the Iberian Chains. A parallel-sided glabella with a subtruncate anterior margin and lacking glabellar furrows represents one of the principal diagnostic features observable in these generally poorly preserved specimens. Within the Hebediscidae, this morphology is more consistent with that of \u003cem\u003eHebediscus\u003c/em\u003e. The diagnosis of the genus provided by Jell (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) includes several characters that cannot be assessed in the specimens from the Hu\u0026eacute;rmeda Formation, such as a pygidium bearing seven or more axial rings. In the present specimens, as well as in \u003cem\u003eHebediscus planus\u003c/em\u003e (Hutchinson, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1962\u003c/span\u003e) and \u003cem\u003eHebediscus williamsi\u003c/em\u003e Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, the number of axial rings is indeterminate.\u003c/p\u003e \u003cp\u003eGeometric morphometric analysis indicates that the specimens from the Hu\u0026eacute;rmeda Formation represent a distinct species of \u003cem\u003eHebediscus\u003c/em\u003e, characterised by a narrow (tr.) glabella in relation to the width (tr.) of the cranidium and by a short (sag.) preglabellar area. Their separation in morphospace is interpreted as intrageneric variation within \u003cem\u003eHebediscus\u003c/em\u003e rather than evidence for generic distinction, as the combination of qualitative characters observed in these specimens supports their assignment to \u003cem\u003eHebediscus\u003c/em\u003e rather than to a separate genus. The results further suggest a distinct cluster of cranidial morphologies among the Newfoundland material, including \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eplanus\u003c/em\u003e, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003ewilliamsi\u003c/em\u003e, two forms left in open nomenclature by Westrop and Landing (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), and a specimen assigned to \u003cem\u003eHebediscus attleborensis\u003c/em\u003e (Shaler and Foerste in Shaler, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e1888\u003c/span\u003e) by Fletcher (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) and Fletcher and Theokritoff (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), indicating a closer morphological affinity among these forms than with other species of the genus. Westrop and Landing (\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) argued that previous assignment of specimens from Newfoundland, Morocco and Siberia to \u003cem\u003eH\u003c/em\u003e. \u003cem\u003eattleborensis\u003c/em\u003e by different authors are unfounded. The results of the morphometric analysis presented here are consistent with this interpretation, given the pronounced separation in Procrustes morphospace between specimens of this species.\u003c/p\u003e \u003cp\u003eAlthough Sep\u0026uacute;lveda et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) considered the specimens from the Hu\u0026eacute;rmeda Formation to represent the first record of the genus in the Iberian Chains, Clausen (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) assigned several cranidia from the Valdemiedes Formation (upper Bilbilian) to juvenile individuals of the ellipsocephalid \u003cem\u003eAlueva undulata\u003c/em\u003e Sdzuy, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e1961\u003c/span\u003e, which probably belong to \u003cem\u003eHebediscus\u003c/em\u003e (see Clausen, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2004\u003c/span\u003e, Fig.\u0026nbsp;2.2\u0026ndash;2.8). These specimens are, however, significantly younger than those from the Hu\u0026eacute;rmeda Formation and other \u003cem\u003eHebediscus\u003c/em\u003e species, although they occupy a stratigraphic position comparable to that of various forms from Morocco tentatively assigned to the genus (see Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp.\u003c/p\u003e \u003cp\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e7\u003c/span\u003ea\u0026ndash;i)\u003c/p\u003e\u003cp\u003e2022 \u003cem\u003eHebediscus\u003c/em\u003e? sp. \u0026ndash; Sep\u0026uacute;lveda et al., pp. 104\u0026ndash;105, fig. 6A\u0026ndash;D.\u003c/p\u003e\n\u003cp\u003e2024 \u003cem\u003eHebediscus\u003c/em\u003e? sp. \u0026ndash; Li\u0026ntilde;\u0026aacute;n et al., p. 725.\u003c/p\u003e\n\u003cp\u003e2024 \u003cem\u003eHebediscus\u003c/em\u003e? sp. \u0026ndash; Geyer, p. 355, fig. 132.\u003c/p\u003e\n\u003cp\u003e2025 \u003cem\u003eHebediscus\u003c/em\u003e? sp. \u0026ndash; Geyer and Landing, p. 25.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEtymology\u003c/strong\u003e. In tribute to Prof. Peter Carls, for his contribution to the knowledge of the geology and paleontology of the Palaeozoic of the Iberian Chains.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHolotype\u003c/strong\u003e. Internal mould of a cranidium (MPZ 2021/366) from the level 2 of the M9 section, lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian, Cambrian Series 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eParatypes\u003c/strong\u003e. Internal mould of two cranidia and one pygidium (MPZ 2021/367\u0026ndash;369) the level 2 of the M9 section, lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian, Cambrian Series 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOther material\u003c/strong\u003e. Three cranidia and one pygidium (MPZ 2026/01\u0026ndash;04) from the level 23 of the MT1 and level 2 of the M9 section, lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian, Cambrian Series 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDiagnosis\u003c/strong\u003e. A species of \u003cem\u003eHebediscus\u003c/em\u003e with a narrow (tr.) glabella with a subtruncate anterior margin; palpebral lobes moderately long (exsag.); preglabellar area short (sag.); anterior margin only slightly curved.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDescription\u003c/strong\u003e. Cranidium subrectangular to subelliptical in outline; length (sag.) about 75% of cranidial width (tr.) across palpebral lobes. Glabella subrectangular and slightly tapering forward, moderately long (sag.), and convex with respect to the rest of the cranidium; length (sag.) about 75% of total cranidial length (sag.); sides faintly concave; width (tr.) at occipital lobe about 35% of cranidial width (tr.) across palpebral lobes; anterior margin flattened. Glabellar furrows obsolescent. Occipital furrow shallow. Occipital lobe relatively short (sag.), subsemicircular in outline, and curved backwards; length (sag.) about 12% of total cranidial length (sag.) and 15% of total glabellar length (sag.). Axial furrow deep and well-marked. Fixigena relatively wide (tr.) and slightly convex; width (tr.) across palpebral lobe about 80% of glabellar width (tr.) across palpebral lobe; moderately sloping up from axial furrow towards palpebral lobe, and sloping down posteriorly towards posterior border. Palpebral lobe moderately long (exsag.) and wide (tr.); length (exsag.) about 30% of total cranidial length (sag.); width (tr.) about 8% of cranidial width (tr.) across palpebral lobe. Eye ridge indistinct. Preocular area and preglabellar field deep and sloping down toward anterior border furrow. Anterior border furrow curved and moderately deep, subequal in depth than axial furrow.; slightly longer (sag.) in front of the glabella. Anterior border curved, convex, and relatively short (sag.); subequal in length all along. Anterior margin moderately curved. Posterior border convex in transverse profile.\u003c/p\u003e\n\u003cp\u003ePygidium subelliptical in outline and convex, with a prominent axis; length (sag.) about 75% of maximum pygidial width (tr.). Pygidial axis subconical and tapering posteriorly; length (sag.) about 85% of total pygidial length (sag.); width (tr.) anteriorly about 160% of pygidial axis width (tr.) posteriorly and about 40% of maximum pygidial width (tr.); posterior margin rounded and almost connected with pygidial border furrow; sides apparently\u0026nbsp;straight. Axial furrow relatively shallow. Pleural field sloping up from lateral border to the axis. Pleural furrow not visible. Lateral and posterior border furrows moderately deep and well-marked all around. Lateral and posterior borders relatively narrow (tr. and sag.), convex, and subequal in length all around, very similar to anterior border of the cranidium. Posterior margin curved.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRemarks\u003c/strong\u003e. Geometric morphometric analysis of cranidial shape demonstrates that the specimens from the lower part of the Hu\u0026eacute;rmeda Formation are clearly distinct from the majority of all previously described species of \u003cem\u003eHebediscus\u003c/em\u003e and can be regarded as representing a new species. These specimens differ from the rest of the species of the genus by a combination of a narrower (tr.) glabella with respect to the width (tr.) of the cranidium and, most notably, by a markedly short (sag.) preglabellar area. The reduced length (sag.) of the preglabellar area results in a less curved anterior cranidial margin, whereas in other species of the genus, such as those from Newfoundland and Siberia, the preglabellar area is conspicuously longer (sag.), and the anterior cranidial margin is distinctly curved or weakly pointed (see Korovnikov, 2007; Fletcher and Theokritoff, 2008; Westrop and Landing, 2011). Although the anterior border is short (sag.) in both the specimens from the Hu\u0026eacute;rmeda Formation and other species of \u003cem\u003eHebediscus\u003c/em\u003e, the preglabellar field is distinctly shorter (sag.) in the former.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA comparably reduced (sag.) preglabellar field is only known in various Moroccan specimens assigned to \u003cem\u003eHebediscus\u003c/em\u003e sp. indet. A and \u003cem\u003eHebediscus\u003c/em\u003e sp. indet. B by Geyer (1988, figs. 2, 3, 83, 84), the latter occurring at a similar stratigraphic position within the \u003cem\u003eSectigena\u003c/em\u003e Zone. These specimens also exhibit a narrow (tr.) glabella relative to the cranidium, closely resembling the specimens from the Hu\u0026eacute;rmeda Formation. Conspecificity between \u003cem\u003eHebediscus\u003c/em\u003e sp. indet. B and the Spanish material is therefore plausible, although the poor preservation of the available pygidia of the latter prevents a detailed comparison with the distinctive pygidium of the Moroccan material. Other material showing a similar reduced (sag.) preglabellar area and a moderately curved anterior cranidial margin includes several specimens from Siberia previously assigned to \u003cem\u003eH. attleborensis\u003c/em\u003e (see Repina, 1972, pl. 33, figs. 1, 2). However, Westrop and Landing (2011) argued that this species should be restricted to its type material from Massachusetts, and the Siberian specimens are therefore unlikely to belong to \u003cem\u003eH. attleborensis\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eH\u003c/em\u003e.\u003cem\u003e\u0026nbsp;lemdadensis\u003c/em\u003e, another species with a comparable stratigraphic range from Morocco, also possesses a cranidium characterised by a relatively short (sag.) preglabellar area, although it appears slightly longer (sag.) than that of the specimens from the Hu\u0026eacute;rmeda Formation. In addition, \u003cem\u003eH\u003c/em\u003e. \u003cem\u003elemdadensis\u003c/em\u003e bears a distinct occipital spine, whereas the Spanish material lacks an occipital spine and shows a smooth posterior margin of the occipital lobe. Material from the Alconera Formation of the Ossa-Morena Zone, studied by Collantes (2023) and Collantes et al. (submitted) and assigned to \u003cem\u003eHebediscus\u003c/em\u003e, occupies a broadly similar stratigraphic position near the base of the upper Marianian. However, the poor preservation of this material prevents a confident comparison, and although the glabella appears narrow (tr.), the preglabellar area is proportionally longer (sag.) than in the specimens from the Hu\u0026eacute;rmeda Formation.\u003c/p\u003e\n\u003cp\u003eOn the basis of the combination of cranidial characters and results of the morphometric analysis, \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. is proposed for the material from the lower part of the Hu\u0026eacute;rmeda Formation.\u003c/p\u003e\n\u003cp\u003eFamily Yukoniidae S. Zhang in W. Zhang et al., 1980\u003c/p\u003e\n\u003cp\u003eGenus \u003cem\u003eHebediscina\u003c/em\u003e Rasetti, 1972\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eType-species\u003c/strong\u003e. \u003cem\u003eHebediscina sardoa\u003c/em\u003e Rasetti, 1972, from Matoppa Formation, Sardinia (Italy), by original designation, Cambrian Series 2.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eHebediscina\u003c/em\u003e? sp.\u003c/p\u003e\n\u003cp\u003e(Figure 7j\u003cstrong\u003e\u0026ndash;\u003c/strong\u003eo)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterial and locality\u003c/strong\u003e. Two cranidia preserved as internal moulds (MPZ 2026/05, 2026/06) from the level 23 of the MT1 section and level 3 of the M9 section, lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian, Cambrian Series 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOther material studied\u003c/strong\u003e. Two cranidia and two pygidia collected by Prof. Klaus Sdzuy in the level 23 of the lowermost Hu\u0026eacute;rmeda Formation in the MT1 section in Tierga (according to the notes presented to Eladio Li\u0026ntilde;\u0026aacute;n and field data). These specimens are currently not available (Gerd Geyer, personal communication, 2021).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDescription and comparison\u003c/strong\u003e. Two small cranidia recovered from the lower part of the Hu\u0026eacute;rmeda Formation exhibit a markedly distinct morphology when compared with that of the co-occurring \u003cem\u003eHebediscus\u003c/em\u003e \u003cem\u003ecarlsi\u0026nbsp;\u003c/em\u003en. sp. These cranidia are characterised by an elongated (sag.) and notably narrow (tr.) glabella with a rounded anterior glabellar margin, attaining a width (tr.) of approximately 25% of the cranidial width (tr.) across the palpebral lobes. In \u003cem\u003eH.\u003c/em\u003e \u003cem\u003ecarlsi\u0026nbsp;\u003c/em\u003en. sp., by contrast, the glabella reaches approximately 35% of the cranidial width (tr.) across the palpebral lobes, and the anterior glabellar margin is subtruncate. Additional differences include a longer (sag.) preglabellar area, comprising a longer (sag.) and distinctly depressed preglabellar field, the presence of well-defined preocular fields, and possibly longer (exsag.) palpebral lobes in the two cranidia discussed herein. Two pygidia collected by Prof. Klaus Sdzuy also differ from the pygidia associated with cranidia of \u003cem\u003eH\u003c/em\u003e\u003cem\u003e. carlsi\u003c/em\u003e n. sp. in having well-defined axial furrows to the sides, resulting in an axis with slightly indented sides. These features suggest that these specimens represent a distinct species and do not fit the typical morphology of \u003cem\u003eHebediscus\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eThe distinctly narrow (tr.) glabella and the presence of well-developed preocular fields observed in these two cranidia suggest their tentative assignment to the Yukoniidae and, more specifically, to \u003cem\u003eHebediscina\u003c/em\u003e Rasetti, 1972. Comparable morphologies are also present in the calodiscid genera \u003cem\u003eNeocobboldia\u003c/em\u003e and \u003cem\u003eKorobovia\u003c/em\u003e. However, members of the Calodiscidae are characterised by a well-defined and complete occipital furrow, which is absent in the specimens from the Hu\u0026eacute;rmeda Formation. In addition, Jell in Bengtson et al. (1990) listed the presence of a glabella without furrows as diagnostic for the genus, a condition which is also present in the specimens from the Hu\u0026eacute;rmeda Formation. The prominent occipital spine that characterises the Yukoniidae, however, cannot be recognised in the present material. Furthermore, although the specimens are poorly preserved, the pygidium appears to possess up to three axial rings plus an articulating half-ring, whereas the diagnoses of \u003cem\u003eHebediscina\u003c/em\u003e and the Yukoniidae provided by Jell (1997) indicate the presence of four to seven axial rings. These discrepancies, in addition to the poor preservation of the material, prevent a confident generic assignment for the specimens from the Hu\u0026eacute;rmeda Formation.\u003c/p\u003e"},{"header":"Biostratigraphy and correlation","content":"\u003cp\u003eAlthough \u003cem\u003eHebediscus\u003c/em\u003e exhibits a broad stratigraphic range in some regions, such as Morocco (see Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Geyer and Landing, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) and Siberia (see Rozanov and Varlamov, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), the majority of species of the genus occur within a broadly comparable stratigraphic interval close to the boundary between Cambrian Stages 3 and 4 (see Geyer and Shergold, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2000\u003c/span\u003e, table 1; Geyer, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). In the Iberian Peninsula, \u003cem\u003eHebediscus\u003c/em\u003e is consistently recorded from the base of the upper Marianian in both the Iberian Chains (see Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; herein) and Ossa Morena Zone (see Collantes, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Collantes et al., submitted). Along the West Gondwana margin, the genus is also present in the \u003cem\u003eSectigena\u003c/em\u003e Zone of Morocco (see Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Geyer and Landing, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), which has been roughly correlated with the upper Marianian of Iberia (see Sundberg et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In Morocco, however, \u003cem\u003eHebediscus\u003c/em\u003e has additionally been reported from older stratigraphic intervals, including the \u003cem\u003eAntatlasia hollardi\u003c/em\u003e and \u003cem\u003eAntatlasia gutta-pluviae\u003c/em\u003e zones, correlated with the lower and middle Marianian (see Sundberg et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), as well as from the younger \u003cem\u003eMorocconus notabilis\u003c/em\u003e Zone, assigned to the Agdzian Stage (see Geyer, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Geyer and Landing, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Avalonia, the type species of the genus comes from the \u003cem\u003eHebediscus attleborensis\u003c/em\u003e Subzone (uppermost \u003cem\u003eCallavia broeggeri\u003c/em\u003e Zone) of the Branchian Series in Massachusetts (see Shaw, \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e1950\u003c/span\u003e; Landing, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Fletcher and Theokritoff, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), which is generally correlated with the upper part of Stage 3 or the lower part of Stage 4 of the Cambrian (see Sundberg et al. \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). \u003cem\u003eHebediscus\u003c/em\u003e is also abundant in Newfoundland, where it also occurs in the uppermost \u003cem\u003eCallavia broeggeri\u003c/em\u003e Zone (see Hutchinson, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1962\u003c/span\u003e; Fletcher, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1972\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In Eastern Avalonia, the genus has been reported from a comparable stratigraphic position within the \u003cem\u003eCallavia\u003c/em\u003e Zone in the Comley Quarry, England (see Cobbold, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1931\u003c/span\u003e; Rushton et al., \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Rushton, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Siberia and Central Asian Orogenic Belt (\u003cem\u003esensu\u003c/em\u003e Zonenshain et al., \u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e1990\u003c/span\u003e), the stratigraphic range of \u003cem\u003eHebediscus\u003c/em\u003e appears to be broader than in Avalonia (Astashkin et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1991\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). The genus has been recorded from the \u003cem\u003eBergeroniellus micmacciformis\u003c/em\u003e-\u003cem\u003eErbiella\u003c/em\u003e Zone (see Rozanov and Varlamov, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), within the lower Botoman stage, which has been correlated with the lower Stage 4 of the Cambrian (see Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Rozanov and Varlamov (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) also reported the occurrence of the genus in the \u003cem\u003eBergerioniaspis ornata\u003c/em\u003e Zone, of a younger age in the upper Botoman stage (see Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and Korovnikov (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) and Korovnikov and Novozhilova (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) indicated its occurrence in the \u003cem\u003eJudomia mattajensis\u003c/em\u003e-\u003cem\u003eUktaspis granulata\u003c/em\u003e Zone, upper Atdabanian, slightly below the proposed boundary between Cambrian Stages 3 and 4 (see Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFinally, Rasetti (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1967\u003c/span\u003e) defined \u003cem\u003eHebediscus marginatus\u003c/em\u003e from the \u003cem\u003eElliptocephala asaphoides\u003c/em\u003e fauna in the Taconic Allochthon. This species is recorded together with \u003cem\u003eSerrodiscus speciosus\u003c/em\u003e (Ford, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1873\u003c/span\u003e) in a level that has been correlated with the upper Marianian (Collantes et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The stratigraphic position of this species would be equivalent to that of \u003cem\u003eHebediscus carlsi\u003c/em\u003e. However, Fritz (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1973\u003c/span\u003e) assigned \u003cem\u003eH\u003c/em\u003e. \u003cem\u003emarginatus\u003c/em\u003e to \u003cem\u003eEkwipagetia\u003c/em\u003e Fritz, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1973\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe geographic distribution of \u003cem\u003eHebediscina\u003c/em\u003e is more restricted than that of \u003cem\u003eHebediscus\u003c/em\u003e. The type material of \u003cem\u003eHebediscina\u003c/em\u003e derives from the Matoppa Formation of Sardinia (see Rasetti, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e1972\u003c/span\u003e), which has an older age and has been correlated with the Ovetian stage (Pillola, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Pillola et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e1995\u003c/span\u003e), a similar age to that of the occurrence of the genus in South China (see Lin, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Zhang and Clarkson, \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In contrast, in Australia the genus occurs in the \u003cem\u003ePararaia janeae\u003c/em\u003e Zone (see Bengtson et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e), which is correlated with the lower Stage 4 of the Cambrian (see Geyer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Laurie et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite local extensions into older and younger intervals, \u003cem\u003eHebediscus\u003c/em\u003e and \u003cem\u003eHebediscina\u003c/em\u003e are characteristic of the interval surrounding the boundary between Cambrian Stages 3 and 4. Several authors have emphasised the potential of \u003cem\u003eHebediscus attleborensis\u003c/em\u003e, together with \u003cem\u003eCalodiscus\u003c/em\u003e, \u003cem\u003eSerrodiscus\u003c/em\u003e, and \u003cem\u003eTriangulaspis\u003c/em\u003e (known as the \u0026ldquo;HCST band\u0026rdquo;), for the intercontinental correlation of this boundary (see Geyer and Shergold, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Geyer, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, the assignment of \u003cem\u003eH. attleborensis\u003c/em\u003e outside its type area in Massachusetts has been widely questioned (see Westrop and Landing, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This topic was also recently discussed by Geyer and Landing (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), who referred to the Moroccan material previously assigned to \u003cem\u003eH. attleborensis\u003c/em\u003e by Hup\u0026eacute; (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1953\u003c/span\u003e) as \u003cem\u003eHebediscus\u003c/em\u003e new species 1. The morphometric results presented herein further support the interpretation that specimens from Morocco, Siberia, and Newfoundland previously assigned to \u003cem\u003eH. attleborensis\u003c/em\u003e represent taxa distinct from the Massachusetts type material. Nevertheless, the generic occurrence of \u003cem\u003eHebediscus\u003c/em\u003e remains a useful biostratigraphic indicator for approximating the lower boundary of Cambrian Stage 4 across several palaeocontinents, including the lower part of the Hu\u0026eacute;rmeda Formation in the Iberian Chains. The presence of \u003cem\u003eHebediscina\u003c/em\u003e additionally provides a tentative correlation with the \u003cem\u003ePararaia janeae\u003c/em\u003e Zone of Australia, where \u003cem\u003eHebediscus\u003c/em\u003e has not been recorded. In this region, \u003cem\u003eHebediscina\u003c/em\u003e occurs in association with \u003cem\u003eSerrodiscus\u003c/em\u003e (Bengtson et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e), a taxon also present at the base of the upper Marianian in the Ossa Morena and Central Iberian zones (see Collantes et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Sep\u0026uacute;lveda et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e8\u003c/span\u003e summarises the paleogeographic distribution of both genera according to the early Cambrian palaeogeographic reconstruction of Pillola (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) and McKerrow et al. (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). \u003cem\u003eHebediscina\u003c/em\u003e is distributed in the redlichiid realm and the intermediate bigotinid realm, whereas \u003cem\u003eHebediscus\u003c/em\u003e is present in the intermediate bigotinid realm and Avalonia.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eNew material recovered from the lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian, Cambrian Series 2) documents the presence of Eodiscida in the Iberian Chains. Landmark-based morphometric analysis of cranidial shape of specimens previously tentatively assigned to \u003cem\u003eHebediscus\u003c/em\u003e, in conjunction with qualitative morphological observations, demonstrates that the material from the Hu\u0026eacute;rmeda Formation represents a distinct species, herein described as \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. This species is characterised by a relatively narrow (tr.) glabella and a markedly short (sag.) preglabellar area, resulting in a less curved anterior cranidial margin. Specimens from the same stratigraphic horizon displaying distinct cranidial morphology are tentatively assigned to \u003cem\u003eHebediscina\u003c/em\u003e, constituting the first record of this genus in the Iberian Peninsula.\u003c/p\u003e \u003cp\u003eResults of the morphometric analysis support previous suggestions that several specimens assigned to \u003cem\u003eHebediscus attleborensis\u003c/em\u003e outside its type area in Massachusetts do not belong to that species, reinforcing the view that \u003cem\u003eH. attleborensis\u003c/em\u003e is unsuitable as a precise intercontinental index taxon. Nevertheless, the generic occurrence of \u003cem\u003eHebediscus\u003c/em\u003e, in association with other taxa, remains a valuable tool for broad correlation of the interval around the Cambrian Stage 3\u0026ndash;4 boundary. The co-occurrence of \u003cem\u003eHebediscus\u003c/em\u003e and \u003cem\u003eHebediscina\u003c/em\u003e in the lower part of the Hu\u0026eacute;rmeda Formation strengthens correlations between the Iberian Chains, the Ossa-Morena Zone, Morocco, Avalonia, Siberia, Central Asian Orogenic Belt, and Australia, and highlights the importance of Eodiscida for refining regional and intercontinental correlations within Cambrian Series 2.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eThis is a contribution to the GIUV2017-395 Research Group of the Universitat de Val\u0026egrave;ncia and to the project IGCPs 652 \u0026ldquo;Reading geologic time in Palaeozoic sedimentary rocks\u0026rdquo;. We are grateful to Ms. Isabel P\u0026eacute;rez Urresti (technician of the University of Zaragoza) who assisted us with the photography.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e. Conceptualization: Alexandre Sep\u0026uacute;lveda, Rodolfo Gozalo; Methodology: Alexandre Sep\u0026uacute;lveda; Formal analysis and investigation: Alexandre Sep\u0026uacute;lveda; Writing - original draft preparation: Alexandre Sep\u0026uacute;lveda; Writing - review and editing: Alexandre Sep\u0026uacute;lveda, Rodolfo Gozalo, Eladio Li\u0026ntilde;\u0026aacute;n, Juan B. Chirivella-Martorell; Data curation: Alexandre Sep\u0026uacute;lveda, Rodolfo Gozalo, Eladio Li\u0026ntilde;\u0026aacute;n, Juan B. Chirivella-Martorell; Visualization: Alexandre Sep\u0026uacute;lveda, Rodolfo Gozalo.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e. This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e. The list of specimens included in the geometric morphometric analyses (catalogue numbers and source publications for images) is provided in Supplementary Information 1. Landmark coordinate data and analysis scripts are not publicly available.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdams, D. C., \u0026amp; Ot\u0026aacute;rola-Castillo, E. 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American Geophysical Union.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":false,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"palaeobiodiversity-and-palaeoenvironments","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pbpe","sideBox":"Learn more about [Palaeobiodiversity and Palaeoenvironments](https://www.springer.com/journal/12549)","snPcode":"12549","submissionUrl":"https://www.editorialmanager.com/pbpe/default2.aspx","title":"Palaeobiodiversity and Palaeoenvironments","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"trilobites, geometric morphometrics, systematics, biostratigraphy, upper Marianian (Cambrian Stage 4, Cambrian Series 2), Iberian Chains (NE Spain)","lastPublishedDoi":"10.21203/rs.3.rs-8653291/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8653291/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Cambrian Series 2 of the Iberian Peninsula is characterised by strong trilobite faunal endemism, which has hindered both regional and intercontinental correlations. In the Iberian Chains (Northeast Spain), the Marianian regional stage deposits of the Ribota and Hu\u0026eacute;rmeda formations contain a trilobite fauna that is still insufficiently studied, despite its considerable biostratigraphic potential. This study documents the occurrence of the globally distributed Eodiscida in the lower part of the Hu\u0026eacute;rmeda Formation (upper Marianian; base of the Stage 4 of the Cambrian). Morphometric analyses of cranidial shape demonstrate that specimens previously tentatively assigned to \u003cem\u003eHebediscus\u003c/em\u003e represent a new species, \u003cem\u003eHebediscus carlsi\u003c/em\u003e n. sp. Additional material from the same horizon is tentatively assigned to \u003cem\u003eHebediscina\u003c/em\u003e, constituting the first record of this genus in the Iberian Peninsula. The presence of \u003cem\u003eHebediscus\u003c/em\u003e and \u003cem\u003eHebediscina\u003c/em\u003e provides a robust basis for correlating the lower part of the Hu\u0026eacute;rmeda Formation with coeval horizons in the West Gondwana margin, Avalonia, Siberia, Central Asian Orogenic Belt, and Australia, contributing to improved regional and intercontinental correlation of Cambrian Series 2 strata.\u003c/p\u003e","manuscriptTitle":"Presence of Eodiscida (Trilobita) in the Cambrian Series 2 of the Iberian Chains (Northeast Spain)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-23 09:52:26","doi":"10.21203/rs.3.rs-8653291/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-01-25T12:53:39+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-21T19:00:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-21T07:11:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Palaeobiodiversity and Palaeoenvironments","date":"2026-01-20T16:52:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"palaeobiodiversity-and-palaeoenvironments","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pbpe","sideBox":"Learn more about [Palaeobiodiversity and Palaeoenvironments](https://www.springer.com/journal/12549)","snPcode":"12549","submissionUrl":"https://www.editorialmanager.com/pbpe/default2.aspx","title":"Palaeobiodiversity and Palaeoenvironments","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a3c4ed56-2c07-4ae8-b1a9-343da8d66052","owner":[],"postedDate":"January 23rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-23T09:52:26+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-23 09:52:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8653291","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8653291","identity":"rs-8653291","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}