The first fossil Dinematichthyidae (life-bearing coral brotulas) from the Early Pliocene of the Tartaro Formation, Luzon, Philippines

The first fossil Dinematichthyidae (life-bearing coral brotulas) from the Early Pliocene of the Tartaro Formation, Luzon, Philippines | 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 The first fossil Dinematichthyidae (life-bearing coral brotulas) from the Early Pliocene of the Tartaro Formation, Luzon, Philippines Werner Schwarzhans, Dominique P. Mediodia, Toby L. Vergara, Abigael L. Castro, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9531350/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 A large number of fossil otoliths have been collected from the Early Pliocene Tartaro Formation on Luzon, Philippines. The fauna is mainly represented by shallow-water fishes and will be described in a sequence of articles to come. Here we begin the sequence with a description of two otolith-based species of the family Dinematichthyidae (life-bearing coral brotulas, Ophidiiformes). They represent the first fossil record of the group from the Indo-West Pacific, which today forms the center of marine biodiversity for fishes and for the family Dinematichthyidae. Two new species are being described: Diancistrus kasei n. sp. and Ungusurculus phasmaticus n. sp. Dinematichthyidae otoliths Philippines Diancistrus Ungusurculus Early Pliocene Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Fossil otoliths from the Philippines have rarely been studied in the past. The most notable report is from van Hinsbergh & Helwerda ( 2019 ) regarding otoliths from the Late Pliocene and Early Pleistocene sedimentary rocks from Pangasinan Province (i.e., Bani and Anda [Cabarruyan Island]), Luzon Island. In recent years, a large number of otoliths from the Early Pliocene Tartaro Formation in the Ilocos-Central Luzon Basin (ICLB) of central Luzon (Fig. 1 – 4 ) have been collected (Mediodia et al., 2025). The Tartaro Formation has yielded a shallow-water fish community as witnessed by otoliths of predominantly Gobioidei and Apogonidae and including those of Dinematichthyidae. Here, we describe the first fossil record of the family Dinematichthyidae in the Philippines and in the Indo-West Pacific. In addition to the rich otolith assemblage recovered from the Tartaro Formation, otoliths have also been collected from Miocene to Pleistocene rocks from other localities on Luzon and other Philippine provinces such as from the Visayas (Panay, Negros, Cebu and Bobol) and Mindanao. In addition, some otoliths were also collected from Java, Indonesia. Most of these localities have yielded shallow water faunal associations, sometimes in the vicinity of coral reefs, which are particularly rich in fish otoliths of the Gobioidei and Apogonidae. Several lineages of these two groups have been retrieved for the first time in the fossil record. They are also rich in todays coral triangle, the center of marine biodiversity, but their otoliths have rarely been studied and figured. Therefore, particular efforts have been undertaken to build a comprehensive collection of extant comparative otoliths from the region in order to facilitate an adequate identification of the fossil specimens. The following sequences of the project will focus first on the Gobioidei in two or more parts, the Apogonidae, the Myctophidae, and other fish families. The Gobioidei and Apogonidae will provide new insights in the evolution of these two large groups of fishes and their ecological adaptation through time. The Myctophidae are of interest for superregional biostratigraphic purposes. In the course of these subsequent articles, emphasis will also be put on depicting otoliths of relevant extant fishes for correlation purposes. Collection Site and Geological Setting The specimens described in this study were collected from bulk sediment samples containing fossil otoliths in the type locality of Tartaro Formation (15°10'14.60"N, 121° 3'7.81" E) along Madlum River, Brgy. Tartaro, San Miguel, Bulacan (Fig. 1 – 4 ). This locality is situated in the southeastern portion of the Ilocos-Central Luzon Basin (ICLB; Fig. 1 ), which is composed of Oligocene to Pleistocene sediments. The ICLB serves as a catchment basin of the sediments from the Luzon Central Cordillera Range (to the east) and Zambales Mountain Range (to the west) (Mines and Geosciences Bureau [MGB], 2010). Tartaro Formation is described as a sequence of gently-dipping greenish-gray calcareous mudstone and poorly consolidated, loosely cemented fossiliferous sandstone (Melendres and Verzosa, 1960; MGB, 2010). The Tartaro Formation unconformably overlies the marine sediments of the Miocene Madlum Formation to the east. It is unconformably overlain by the shallow marine Pleistocene Alat Conglomerate Member of the Guadalupe Formation to the west (Gonzales et al., 1971 in Kase and Aguilar, 2006 ) (Fig. 4 ). Kase and Aguilar ( 2006 ) reported a late Early Pliocene age along the Madlum River using calcareous nannofossils. Using Sato’s (1999) calibration of planktonic and microfossil biostratigraphy against the revised Cenozoic magnetostratigraphy, the age of the sediments from which the otoliths were obtained was constrained approximately between 3.6 to 3.75 Ma (Kase and Aguilar, 2006 ). Various mollusks have been recorded from Tartaro Formation, including Melongena gigas and Strombus maximus (Kanno et al., 1982 ), Bulacanites obtusiplicatus (Kase & Aguilar, 2006 ), and Calyptraphorus sp. (Kase & Aguilar, 2014 ). In addition, brain corals ( Porites sp.) and mushroom corals ( Fungia spp.) were also reported from the formation (Kase & Aguilar, 2014 ). Oxygen isotope analysis of well-preserved Porites coral fossils from the Tartaro Formation was used to contradict the existence of a “permanent El Niño” condition during the Pliocene warm period (Watanabe et al., 2011 ). Tartaro Formation was likely deposited in a shallow, nearshore lagoonal environment (Kase & Aguilar, 2006 ; MGB, 2010). The exposure of the Tartaro Formation along Madlum River documents a lithological succession of limestone, marlstone, and sandy to silty mudstone. The fossil fish otoliths were recovered from four localities within the unconsolidated and disaggregated mudstone layer, 1 meter below the marlstone (localities 1–4; Fig. 2 – 4 ). Other fossils were also recovered, including fish remains (i.e., teeth, scales, dermal denticles, and vertebrae), echinoid spines, shell fragments (dominated by gastropods and bivalves), and bryozoans. Large benthic foraminifers (e.g., Order Rotaliida) and ostracods (e.g., Family Bairdiidae) were also recovered from the sediment samples. Material and Methods Photographs of the otoliths were captured with a Canon EOS 1000D that was mounted on a Wild M400 photomacroscope and remotely controlled from a computer. Individual pictures of every view of the objects taken at ranges of depths of field were stacked using Helicon Soft’s Helicon Focus software. When necessary, retouching and adjustments to exposure and contrast were made in Adobe Photoshop to enhance the images without altering any morphological features. The morphological terminology follows that of Koken ( 1884 ) with amendments by Chaine & Duvergier ( 1934 ) and Schwarzhans ( 1978 ). The abbreviations used are OL = otolith length, OH = otolith height, OT = otolith thickness, OCL = length of ostial colliculum, CCL = length of caudal colliculum, OCH = height of ostial colliculum, CCH = height of caudal colliculum, and SuL = sulcus length. The specimens described in the following section are housed at the National Museum of the Philippines (NMP) and NIGS-UP Geology Alumni Association (UPGAA) Geology Museum of the National Institute of Geological Sciences, College of Science, University of the Philippines (NIGSPAL). Extant otoliths depicted for comparison originated from voucher specimens at the Australian Museum, Sydney, Australia (AMS), the National Museum of Natural History, Washington D.C., U.S.A. (USNM), and the Western Australian Museum, Perth, Australia (WAM). Systematic part (by Schwarzhans, Mediodia and Fernando) Order Ophidiiformes Berg, 1937 Family Dinematichthyidae Whitley, 1928, sensu Møller et al., 2016 Genus Diancistrus Ogilby, 1899 Diancistrus kasei n. sp. Schwarzhans, Mediodia & Fernando Figure 5 A–F Holotype Figure 5 C–D, NMP-2519, San Miguel River (locality 1), Brgy. Sibul, San Miguel, Bulacan, Tartaro Formation, Early Pliocene. Paratypes 3 specimens, Fig. 5 A–B, E–F, NMP-2520 and NIGSPAL-FISH-010, same data as holotype. Name In honor of Tomoki Kase (Tokyo), in recognition of his contribution to the paleontology of the late Cenozoic of the Philippines and his providing of fossil otoliths. Diagnosis : OL:OH = 1.95–2.0; OH:OT = 2.3–2.6. Shape elongate fusiform with pointed anterior and slightly broader posterior tip. Dorsal and ventral rims regularly curved. Sulcus almost centrally positioned on inner face, with single colliculum; OL:SuL = 2.4–2.6. Sulcus inclined at 5–7° against sulcus axis. Outer face nearly flat. Description Small elongate fusiform otoliths reaching a size of about 2.5 mm in length (holotype 2.0 mm). Anterior tip pointed, axially positioned; posterior tip nearly symmetrical to anterior tip but more extended and broader. Dorsal rim gently curving, slightly concave above anterior tip, with broadly rounded pre- and postdorsal regions and without distinct angles. Postdorsal rim nearly straight, inclined at about 25 to 32°. Ventral rim regularly curved, deepest at or slightly in front of its middle. All rims smooth and sharp. Inner face distinctly convex, relatively smooth, with nearly centrally positioned, small, shallow, oval sulcus filled with single shallow colliculum. Sulcus slightly inclined against sulcus axis (5–7°). Dorsal depression very indistinct, marked with feeble crista superior against sulcus. Ventral furrow weak, very close to ventral rim of otolith, turning upwards and inwards anteriorly towards anterior tip of sulcus. Outer face flat to slightly convex, smooth. Discussion : Diancistrus kasei represents a typical otolith pattern of the genus Diancistrus characterized by a sulcus with a single colliculum, a fusiform otolith shape with a pointed anterior tip and a broader, somewhat expanded posterior tip and a smooth and convex inner face. The genus Diancistrus contains many extant species (see Schwarzhans, Møller & Nielsen, 2005 ) in the Indo-West Pacific of which the otoliths cannot always be clearly distinguished. The otoliths of Diancistrus kasei , however, are relatively easily distinguished by the combination of a very short sulcus (OL:SuL = 2.4–2.6), a low ratio OL:OH of 1.95–2.0 and the rather regularly curved dorsal rim without distinct angles. Few extant Diancistrus species have otoliths with similarly small sulci, in particular D. erythraeus (Fowler, 1946) (Fig. 5 G–H), D. leisi Schwarzhans, Møller & Nielsen, 2005 (Fig. 5 I–J) and certain specimens attributed to D. machidai Schwarzhans, Møller & Nielsen, 2005 (Fig. 5 K–L); the latter species is currently under review (ongoing research). The otoliths of D. leisi are more elongate than those of D. kasei (OL:OH = 2.05–2.1 vs. 1.95–2.0) and have a distinct postdorsal angle followed by a broad indentation of the postdorsal rim. Otoliths of D. erythraeus are similar to D. kasei in proportions but differ in the presence of a rounded postdorsal angle followed by a small indentation of the postdorsal rim and in the broadly rounded, blunt posterior tip of the otolith. The otolith here figured from D. cf. machidai from off the Batanes Islands, northern Philippines, resembles closest in size and shape of the sulcus and the gently curved development of the postdorsal rim but is slightly more elongate than D. kasei with a more strongly expanded posterior rim (OL:OH = 2.1 vs. 1.95–2.0). We assume that D. kasei is closest related to D . cf. machidai from the Batanes Islands. Genus Ungusurculus Schwarzhans & Møller, 2007 Ungusurculus phasmaticus n. sp. Schwarzhans, Mediodia & Fernando Figure 5 M–P Holotype Figure 5 M–N, NMP-2521, San Miguel River (locality 1), Brgy. Sibul, San Miguel, Bulacan, Tartaro Formation, Early Pliocene. Paratypes 2 specimens, Fig. 5 O–P, NMP-2522 and NIGSPAL-FISH-011, same data as holotype. Name From phasmaticus (Latin) = hidden, difficult to see, referring to the weakly expressed differentiation into ostium and cauda. Diagnosis : OL:OH = 2.05–2.15; OH:OT = 2.3–2.5. Shape elongate with pointed anterior and posterior tips. Dorsal rim flat and horizontal along long central section, with rounded predorsal and sharp postdorsal angle; pre- and postdorsal section of dorsal rim concave. Sulcus positioned asymmetrical anterior of middle of inner face, divided in weakly defined long ostial and short caudal colliculi; OL:SuL = 1.95–2.05; OCL:CCL = 3.5–3.8. Sulcus inclined at 5° against sulcus axis. Outer face slightly concave or flat. Description Small elongate otoliths reaching a size of about 2.15 mm in length (holotype). Anterior tip pointed, slightly supramedian; posterior tip nearly symmetrical to anterior tip but less pointed and slightly expanded. Dorsal rim flat, horizontal along about two-thirds of length, i.e., central portion; anteriorly concave above anterior tip and ascending at about 45° to rounded predorsal angle; posteriorly concave after sharp postdorsal angle and descending at about 35–42° to posterior tip of otolith. Ventral rim regularly curved, deepest at about its middle. All rims smooth and sharp. Inner face distinctly convex, relatively smooth, with slightly anteriorly shifted, moderately long, shallow sulcus filled showing a subtle distinction into a long, wide ostial colliculum and a short, narrower caudal colliculum; OCL:CCL = 3.5–3.8; OCH:CCH about 1.6. Sulcus slightly inclined against sulcus axis at 5°. Dorsal depression very indistinct, marked with feeble crista superior against sulcus. Ventral furrow weak, very close to ventral rim of otolith, turning upwards and inwards anteriorly towards anterior tip of sulcus. Outer face flat or slightly concave, smooth. Discussion The genus Ungusurculus was established based on a specialized organization of the pseudoclaspers, i.e., of a forked inner pseudoclasper. In some species, the forked inner pseudoclasper interlocks with a denticle on the proximal side of the outer pseudoclasper, forming an advanced capturing system. However, in two specimens, the forked inner pseudoclasper faces away from the outer pseudoclasper and does not interlock with a feature on the proximal side of the outer pseudoclasper ( U. philippinensis Schwarzhans & Møller, 2007, and U. williamsi Schwarzhans & Møller, 2007). Otoliths of Ungusurculus are characterized by a long, flat, horizontal dorsal rim with rounded predorsal and variably developed postdorsal angles and a sulcus with a single, fused colliculum. The only exception from this pattern is U. philippinensis (Fig. 5 Q–R), which shows a rounded dorsal rim and a separate, albeit very small caudal colliculum. Because of the combination of pseudoclasper and otolith patterns, U. philippinensis may be considered the most primitive species in the genus. Now, U. phasmaticus is intermediate in its otolith morphology between U. philippinensis and the morphologically more advanced species by combining the flat, long, horizontal dorsal rim with a sulcus that shows a subtle differentiation into a longer and wider ostium and a shorter and narrower cauda, a combination which clearly distinguishes it from all other species of the genus. Conclusions and Outlook This is the first report of otoliths found in the prolific Early Pliocene Tartaro Formation of Luzon, Philippines. It contains the first fossil record of Dinematichthyidae from the Indo-West Pacific, documenting that the genera Diancistrus and Ungusurculus have been firmly established in the region since that time. Dinematichthyid otoliths are relatively rare in the fossil record owing to their cryptic lifestyle in reefs and on abrasive coasts, both environments that do not favor fossilization. So far, fossil dinematichthyid otoliths have been recorded since the early Oligocene of Europe (Nolf, 2013 ) and the Miocene of Central America (Schwarzhans & Aguilera, 2016 ). In addition, a large assemblage of otoliths will be described from this and older strata from the Philippines in further articles under preparation, which will highlight the evolution of shallow-water fish communities in the region, known to constitute the center of marine biodiversity today (Hoeksema, 2007). Declarations Conflict of Interest and Funding The authors declare that they have no conflict of interest. This study was supported by the Emerging Interdisciplinary Research (EIDR) Program “Discovering the world of first hominins in the Philippines – geology, palaeoenvironment, and palaeoecology of archaic hominins in the Philippines – Project 3: Geological Environments” (OVPAA-EIDR Code EIDR-C08-008) under the Office of the Vice President for Academic Affairs of the University of the Philippines to AGSF. Data availability All materials studied, described and figured in this manuscript have been registered and deposited in public institutional scientific collections. All other data are contained in the text. Acknowledgements We want to extend our gratitude to the Mines and Geosciences Bureau (MGB), the National Museum of the Philippines, the National Institute of Geological Sciences, and the University of the Philippines. We cordially thank Tomoki Kase (National Science Museum, Tokyo) for generously providing rich otolith samples from the Tartaro Formation and important geographic and stratigraphic information to the sampled localities. Tomoki Kase and Steffen Kiel (Swedish Museum of Natural History, Stockholm) also kindly provided otoliths from other localities than the Tartaro Formation, which will be described in forthcoming sequences of the project. We are grateful for the support of Chien-Hsiang Lin (Biodiversity Research Center, Academia Sinica). We are also grateful to Chia-Hsin Hsu, Joeven Calvelo, John Phillip Baguio, Antero Borja II, Meyrick Tablizo, David Policarpio for their assistance during the collection and sample preparation. Meyrick U. Tablizo also kindly prepared the geological map depicted in Fig. 1. The senior author thanks Jeff M. Leis, Mark A. McGrouther and Tom Trnski (AMS), Susan L. Jewett and Jeffrey T. Williams (USNM), and Gerald R. Allen, J. Barry Hutchinson and Sue Morrison (WAM) for providing access to extracting otoliths from certain extant voucher fish specimens. References Chaine, J., & Duvergier, J. (1934). – Recherches sur les otolithes des poissons. Etude descriptive et comparative de la sagitta des téléostéens. Actes de la Société linnéenne de Bordeaux , 86 , 1–254. Gonzales, B. A., Ocampo, V. P., & Espiritu, E. A. (1971). – Geology of southeastern Nueva Ecija and eastern Bulacan provinces, Luzon Central Valley. Journal of the Geological Society of the Philippines , 25 (2), 2–41. Hoeksma, B. W. (2007). – Delineation of the Indo-Malayan centre of maximum marine biodiversity: The Coral Triangle. In W. Renema (Ed.), Biogeography, Time, and Place: Distributions, Barriers, and Islands (pp. 117–178). Springer. Kanno, S., O’Hara, S., & Caagusan, N. L. (1982). – Molluscan fauna from the Tartaro Formation (Upper Miocene) of central Luzon, Philippines. Geology and Paleontology of Southeast Asia , 24 , 51–128. Kase, T., & Aguilar, Y. M. (2014). – The Gastropod Genus Calyptraphorus (Rostellariidae: Stromboidea: Mollusca): A Lazarus Taxon from the Pliocene of the Philippines. Paleontological Research , 18 (3), 169–175. Kase, T., & Aguilar, Y. (2006). – Bulacanites obtusiplicatus gen. et sp. nov., a large lucinid bivalve (Mollusca) from the Pliocene of Central Luzon, Philippines. Memoirs of the National Science Museum , 44 (Tokyo), 175–183. Koken, E. (1884). – Über Fisch-Otolithen, insbesondere über diejenigen der norddeutschen Oligocän-Ablagerungen. Zeitschrift der Deutschen Geologischen Gesellschaft , 36 , 500–565. Mediodia, D., Castro, A., Tablizo, M., Policarpio, D., Calvelo, J., Baguio, J. P., Borja, A., Lin, C., & Fernando, A. G. (2024). – Paleoichthyology in the Philippines: A review of Cenozoic fish fossils with insights on its current status and future opportunities. 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(1978). – Otolith-morphology and its usage for higher systematical units with special reference to the Myctophiformes s.l. Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie , 15 , 167–185. Schwarzhans, W., & Aguilera, O. A. (2016). – Otoliths of the Ophidiiformes from the Neogene of tropical America. Palaeo Ichthyologica , 14 , 91–124. Schwarzhans, W., & Møller, P. R. (2007). – Review of the Dinematichthyini (Teleostei: Bythitidae) of the Indo-west Pacific. Part III. Beaglichthys, Brosmolus, Monothrix and eight new genera with description of 20 new species. The Beagle, Records of the Museums and Art Galleries of the Northern Territory , 23: 29–110. Schwarzhans, W., Møller, P. R., & Nielsen, J. G. (2005). – Review of the Dinematichthyini (Teleostei: Bythitidae) of the Indo-West Pacific. Part I. Diancistrus and two new genera with 26 new species. The Beagle Records of the Museums and Art Galleries of the Northern Territory , 21 , 73–163. van Hinsbergh, V. W. M., & Helwerda, R. A. (2019). – Fish otoliths from the Cabarruyan Piacenzian-Gelasian fauna found in the Philippines. Zootaxa , 4563 , 401–443. Watanabe, T., Suzuki, A., Minobe, S., Kawashima, T., Kameo, K., Minoshima, K., Aguilar, Y. M., Wani, R., Kawahata, H., Sowa, K., Nagai, T., & Kase, T. (2011). – Permanent El Niño during the Pliocene warm period not supported by coral evidence. Nature , 471 (7337), 209–211. https://doi.org/10.1038/nature09777 Captions Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 06 May, 2026 Reviewers invited by journal 06 May, 2026 Editor assigned by journal 27 Apr, 2026 First submitted to journal 26 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9531350","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":635366303,"identity":"16f696ba-a9eb-4b37-b5dd-f22097c8289a","order_by":0,"name":"Werner Schwarzhans","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5ElEQVRIiWNgGAWjYJACZjDJ3gAiLXhApARxWngOgxWTokUiGaEYrxaDG+kPPxe22eXLz3x/gOHjDgkZc/YGxhsf8GrJMZae2ZZs2Tg7mYFx5hkJHsueA8yWM/BoMbudw8bMu43ZgFk6mf03b5sEj8GNBDZpHrxa0p8BtdQbsEkeZmAGa7n/gE36D14tCWZALYcNeCSYoVpuMLBJ4/O+/f03xtK8/44bSPAkGzDOBGk5k9hs2YNHi2TP8Yefec5UG8i3H3zA8LHNxt7g+OGDN37gswYLYGwgUcMoGAWjYBSMAnQAAKcTQibhyI92AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-4842-7989","institution":"Natural History Museum of Denmark Zoological Museum: Statens Naturhistoriske Museum Zoologisk Museum","correspondingAuthor":true,"prefix":"","firstName":"Werner","middleName":"","lastName":"Schwarzhans","suffix":""},{"id":635366304,"identity":"d1311863-bf84-4ee0-9066-700a5473d882","order_by":1,"name":"Dominique P. 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Gardoña","email":"","orcid":"","institution":"UP Diliman: University of the Philippines Diliman","correspondingAuthor":false,"prefix":"","firstName":"Audric","middleName":"Brian R.","lastName":"Gardoña","suffix":""},{"id":635366308,"identity":"3fa3752f-3cbd-4de8-9e73-e38c10b36b84","order_by":5,"name":"Jaan Ruy Conrad P. Nogot","email":"","orcid":"","institution":"National Museum of the Philippines","correspondingAuthor":false,"prefix":"","firstName":"Jaan","middleName":"Ruy Conrad P.","lastName":"Nogot","suffix":""},{"id":635366309,"identity":"95c42e07-660d-41f6-a312-b3da8a449215","order_by":6,"name":"Aryssa Orven E. Martin","email":"","orcid":"","institution":"National Museum of the Philippines","correspondingAuthor":false,"prefix":"","firstName":"Aryssa","middleName":"Orven E.","lastName":"Martin","suffix":""},{"id":635366310,"identity":"3e58585d-9ce9-4575-a23b-8671f8bf1752","order_by":7,"name":"Allan Gil S. Fernando","email":"","orcid":"","institution":"UP Diliman: University of the Philippines Diliman","correspondingAuthor":false,"prefix":"","firstName":"Allan","middleName":"Gil S.","lastName":"Fernando","suffix":""}],"badges":[],"createdAt":"2026-04-26 11:00:51","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9531350/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9531350/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109291250,"identity":"f1e343f2-3eec-417a-b646-b2f7a3e5ba38","added_by":"auto","created_at":"2026-05-15 07:40:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":71506697,"visible":true,"origin":"","legend":"\u003cp\u003eSimplified geological map of the central part of the Luzon Island, Philippines, depicting the Ilocos-Central Luzon Basin (ICLB) and the Cagayan Valley Basin (CVB). The Tartaro Formation section in the ICLB is highlighted and the red quadrangle represents the area shown in Fig. 2. Areas not colored represent volcanic rocks and ophiolites.\u003c/p\u003e","description":"","filename":"Fig.1map.png","url":"https://assets-eu.researchsquare.com/files/rs-9531350/v1/024450f70b6e67431b74d797.png"},{"id":109291246,"identity":"fc7c2f78-cc4a-4653-85ee-a79ecf9ea9c8","added_by":"auto","created_at":"2026-05-15 07:40:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":80366270,"visible":true,"origin":"","legend":"\u003cp\u003eTopographic map showing the sampling site in Tartaro Formation, Bulacan, Luzon, Philippines. Philippines index map to the left and detailed map depicting localities sampled for otoliths to the right. In this report, all otoliths were obtained from locality 1.\u003c/p\u003e","description":"","filename":"Fig.2locationmapnewwithtopo.png","url":"https://assets-eu.researchsquare.com/files/rs-9531350/v1/642213687c6886f51afe390c.png"},{"id":109291247,"identity":"ba6c5653-a2dd-44ee-a328-20aca97281bb","added_by":"auto","created_at":"2026-05-15 07:40:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":39280820,"visible":true,"origin":"","legend":"\u003cp\u003ePhotograph of collection site 1 on the right river banks of the San Miguel River upstream of the Sibul road bridge.\u003c/p\u003e","description":"","filename":"Fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-9531350/v1/94facc3ddd7b8c7c6c13803d.png"},{"id":109296389,"identity":"85df594e-aa95-4479-92cb-78caa78ab534","added_by":"auto","created_at":"2026-05-15 08:46:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2857937,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic column of the Central Luzon Valley Basin, Tartaro region (modified from MGB, 2010). Generalized stratigraphic column on the left, schematized Tartaro Formation section along the San Miguel River on the right, composed from data kindly made available by Tomoki Kase.\u003c/p\u003e","description":"","filename":"Fig.4stratigraphy.png","url":"https://assets-eu.researchsquare.com/files/rs-9531350/v1/29d9d827b6a9028356970044.png"},{"id":109291249,"identity":"84f8a2c9-3e95-432f-9381-f43afc39ab07","added_by":"auto","created_at":"2026-05-15 07:40:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":17173420,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA–F\u003c/strong\u003e\u003cem\u003e Diancistrus kasei \u003c/em\u003en. sp., Tartaro Formation, Early Pliocene, Bulacan, Philippines; \u003cstrong\u003eC–D\u003c/strong\u003e holotype, NMP-2519; \u003cstrong\u003eA–B, E–F\u003c/strong\u003e paratypes, NMP-2520 and NIGSPAL-FISH-010. \u003cstrong\u003eG–H\u003c/strong\u003e \u003cem\u003eDiancistrus erythraeus\u003c/em\u003e (Fowler, 1946), USNM 374199, 24°27'N-124°12'E, extant. \u003cstrong\u003eI–J\u003c/strong\u003e \u003cem\u003eDiancistrus leisi\u003c/em\u003e Schwarzhans, Møller \u0026amp; Nielsen, 2005, AMS I. 33708062 10°60'S-144°01'E, extant. \u003cstrong\u003eK–L\u003c/strong\u003e \u003cem\u003eDiancistrus \u003c/em\u003ecf. \u003cem\u003emachidai\u003c/em\u003e Schwarzhans, Møller \u0026amp; Nielsen, 2005, USNM 374181, 20°24'N-121°56'E, extant. \u003cstrong\u003eM–P\u003c/strong\u003e \u003cem\u003eUngusurculus phasmaticus\u003c/em\u003e n. sp., Tartaro Formation, Early Pliocene, Bulacan, Philippines; \u003cstrong\u003eM–N\u003c/strong\u003e holotype, NMP-2521; \u003cstrong\u003eO–P \u003c/strong\u003eparatypes, NMP-2522 and NIGSPAL-FISH-011. \u003cstrong\u003eQ–R\u003c/strong\u003e \u003cem\u003eUngusurculus philippinensis\u003c/em\u003eSchwarzhans \u0026amp; Møller, 2007, holotype, WAM.31397-010, 12°16'N-119°51'E.\u003c/p\u003e","description":"","filename":"Fig.5DinematichthyidaePhilippines.png","url":"https://assets-eu.researchsquare.com/files/rs-9531350/v1/49de46002beb2de754c9d92d.png"}],"financialInterests":"","formattedTitle":"The first fossil Dinematichthyidae (life-bearing coral brotulas) from the Early Pliocene of the Tartaro Formation, Luzon, Philippines","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFossil otoliths from the Philippines have rarely been studied in the past. The most notable report is from van Hinsbergh \u0026amp; Helwerda (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) regarding otoliths from the Late Pliocene and Early Pleistocene sedimentary rocks from Pangasinan Province (i.e., Bani and Anda [Cabarruyan Island]), Luzon Island. In recent years, a large number of otoliths from the Early Pliocene Tartaro Formation in the Ilocos-Central Luzon Basin (ICLB) of central Luzon (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e) have been collected (Mediodia et al., 2025). The Tartaro Formation has yielded a shallow-water fish community as witnessed by otoliths of predominantly Gobioidei and Apogonidae and including those of Dinematichthyidae. Here, we describe the first fossil record of the family Dinematichthyidae in the Philippines and in the Indo-West Pacific.\u003c/p\u003e \u003cp\u003eIn addition to the rich otolith assemblage recovered from the Tartaro Formation, otoliths have also been collected from Miocene to Pleistocene rocks from other localities on Luzon and other Philippine provinces such as from the Visayas (Panay, Negros, Cebu and Bobol) and Mindanao. In addition, some otoliths were also collected from Java, Indonesia. Most of these localities have yielded shallow water faunal associations, sometimes in the vicinity of coral reefs, which are particularly rich in fish otoliths of the Gobioidei and Apogonidae. Several lineages of these two groups have been retrieved for the first time in the fossil record. They are also rich in todays coral triangle, the center of marine biodiversity, but their otoliths have rarely been studied and figured. Therefore, particular efforts have been undertaken to build a comprehensive collection of extant comparative otoliths from the region in order to facilitate an adequate identification of the fossil specimens. The following sequences of the project will focus first on the Gobioidei in two or more parts, the Apogonidae, the Myctophidae, and other fish families. The Gobioidei and Apogonidae will provide new insights in the evolution of these two large groups of fishes and their ecological adaptation through time. The Myctophidae are of interest for superregional biostratigraphic purposes. In the course of these subsequent articles, emphasis will also be put on depicting otoliths of relevant extant fishes for correlation purposes.\u003c/p\u003e"},{"header":"Collection Site and Geological Setting","content":"\u003cp\u003eThe specimens described in this study were collected from bulk sediment samples containing fossil otoliths in the type locality of Tartaro Formation (15\u0026deg;10'14.60\"N, 121\u0026deg; 3'7.81\" E) along Madlum River, Brgy. Tartaro, San Miguel, Bulacan (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This locality is situated in the southeastern portion of the Ilocos-Central Luzon Basin (ICLB; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which is composed of Oligocene to Pleistocene sediments. The ICLB serves as a catchment basin of the sediments from the Luzon Central Cordillera Range (to the east) and Zambales Mountain Range (to the west) (Mines and Geosciences Bureau [MGB], 2010). Tartaro Formation is described as a sequence of gently-dipping greenish-gray calcareous mudstone and poorly consolidated, loosely cemented fossiliferous sandstone (Melendres and Verzosa, 1960; MGB, 2010). The Tartaro Formation unconformably overlies the marine sediments of the Miocene Madlum Formation to the east. It is unconformably overlain by the shallow marine Pleistocene Alat Conglomerate Member of the Guadalupe Formation to the west (Gonzales et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1971\u003c/span\u003e in Kase and Aguilar, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Kase and Aguilar (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) reported a late Early Pliocene age along the Madlum River using calcareous nannofossils. Using Sato\u0026rsquo;s (1999) calibration of planktonic and microfossil biostratigraphy against the revised Cenozoic magnetostratigraphy, the age of the sediments from which the otoliths were obtained was constrained approximately between 3.6 to 3.75 Ma (Kase and Aguilar, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eVarious mollusks have been recorded from Tartaro Formation, including \u003cem\u003eMelongena gigas\u003c/em\u003e and \u003cem\u003eStrombus maximus\u003c/em\u003e (Kanno et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1982\u003c/span\u003e), \u003cem\u003eBulacanites obtusiplicatus\u003c/em\u003e (Kase \u0026amp; Aguilar, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), and \u003cem\u003eCalyptraphorus\u003c/em\u003e sp. (Kase \u0026amp; Aguilar, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In addition, brain corals (\u003cem\u003ePorites\u003c/em\u003e sp.) and mushroom corals (\u003cem\u003eFungia\u003c/em\u003e spp.) were also reported from the formation (Kase \u0026amp; Aguilar, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Oxygen isotope analysis of well-preserved \u003cem\u003ePorites\u003c/em\u003e coral fossils from the Tartaro Formation was used to contradict the existence of a \u0026ldquo;permanent El Ni\u0026ntilde;o\u0026rdquo; condition during the Pliocene warm period (Watanabe et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Tartaro Formation was likely deposited in a shallow, nearshore lagoonal environment (Kase \u0026amp; Aguilar, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; MGB, 2010). The exposure of the Tartaro Formation along Madlum River documents a lithological succession of limestone, marlstone, and sandy to silty mudstone. The fossil fish otoliths were recovered from four localities within the unconsolidated and disaggregated mudstone layer, 1 meter below the marlstone (localities 1\u0026ndash;4; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Other fossils were also recovered, including fish remains (i.e., teeth, scales, dermal denticles, and vertebrae), echinoid spines, shell fragments (dominated by gastropods and bivalves), and bryozoans. Large benthic foraminifers (e.g., Order Rotaliida) and ostracods (e.g., Family Bairdiidae) were also recovered from the sediment samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003ePhotographs of the otoliths were captured with a Canon EOS 1000D that was mounted on a Wild M400 photomacroscope and remotely controlled from a computer. Individual pictures of every view of the objects taken at ranges of depths of field were stacked using Helicon Soft\u0026rsquo;s Helicon Focus software. When necessary, retouching and adjustments to exposure and contrast were made in Adobe Photoshop to enhance the images without altering any morphological features.\u003c/p\u003e \u003cp\u003eThe morphological terminology follows that of Koken (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1884\u003c/span\u003e) with amendments by Chaine \u0026amp; Duvergier (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1934\u003c/span\u003e) and Schwarzhans (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). The abbreviations used are OL\u0026thinsp;=\u0026thinsp;otolith length, OH\u0026thinsp;=\u0026thinsp;otolith height, OT\u0026thinsp;=\u0026thinsp;otolith thickness, OCL\u0026thinsp;=\u0026thinsp;length of ostial colliculum, CCL\u0026thinsp;=\u0026thinsp;length of caudal colliculum, OCH\u0026thinsp;=\u0026thinsp;height of ostial colliculum, CCH\u0026thinsp;=\u0026thinsp;height of caudal colliculum, and SuL\u0026thinsp;=\u0026thinsp;sulcus length.\u003c/p\u003e \u003cp\u003eThe specimens described in the following section are housed at the National Museum of the Philippines (NMP) and NIGS-UP Geology Alumni Association (UPGAA) Geology Museum of the National Institute of Geological Sciences, College of Science, University of the Philippines (NIGSPAL). Extant otoliths depicted for comparison originated from voucher specimens at the Australian Museum, Sydney, Australia (AMS), the National Museum of Natural History, Washington D.C., U.S.A. (USNM), and the Western Australian Museum, Perth, Australia (WAM).\u003c/p\u003e \u003cp\u003e \u003cb\u003eSystematic part\u003c/b\u003e (by Schwarzhans, Mediodia and Fernando)\u003c/p\u003e \u003cp\u003eOrder Ophidiiformes Berg, 1937\u003c/p\u003e \u003cp\u003eFamily Dinematichthyidae Whitley, 1928, sensu M\u0026oslash;ller et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e\u003c/p\u003e \u003cp\u003eGenus \u003cem\u003eDiancistrus\u003c/em\u003e Ogilby, 1899\u003c/p\u003e \u003cp\u003e \u003cb\u003eDiancistrus kasei\u003c/b\u003e \u003cb\u003en. sp. Schwarzhans, Mediodia \u0026amp; Fernando\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;F\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eHolotype\u003c/strong\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC\u0026ndash;D, NMP-2519, San Miguel River (locality 1), Brgy. Sibul, San Miguel, Bulacan, Tartaro Formation, Early Pliocene.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eParatypes\u003c/strong\u003e \u003cp\u003e3 specimens, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;B, E\u0026ndash;F, NMP-2520 and NIGSPAL-FISH-010, same data as holotype.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eName\u003c/strong\u003e \u003cp\u003eIn honor of Tomoki Kase (Tokyo), in recognition of his contribution to the paleontology of the late Cenozoic of the Philippines and his providing of fossil otoliths.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDiagnosis\u003c/b\u003e: OL:OH\u0026thinsp;=\u0026thinsp;1.95\u0026ndash;2.0; OH:OT\u0026thinsp;=\u0026thinsp;2.3\u0026ndash;2.6. Shape elongate fusiform with pointed anterior and slightly broader posterior tip. Dorsal and ventral rims regularly curved. Sulcus almost centrally positioned on inner face, with single colliculum; OL:SuL\u0026thinsp;=\u0026thinsp;2.4\u0026ndash;2.6. Sulcus inclined at 5\u0026ndash;7\u0026deg; against sulcus axis. Outer face nearly flat.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eDescription\u003c/strong\u003e \u003cp\u003eSmall elongate fusiform otoliths reaching a size of about 2.5 mm in length (holotype 2.0 mm). Anterior tip pointed, axially positioned; posterior tip nearly symmetrical to anterior tip but more extended and broader. Dorsal rim gently curving, slightly concave above anterior tip, with broadly rounded pre- and postdorsal regions and without distinct angles. Postdorsal rim nearly straight, inclined at about 25 to 32\u0026deg;. Ventral rim regularly curved, deepest at or slightly in front of its middle. All rims smooth and sharp.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eInner face distinctly convex, relatively smooth, with nearly centrally positioned, small, shallow, oval sulcus filled with single shallow colliculum. Sulcus slightly inclined against sulcus axis (5\u0026ndash;7\u0026deg;). Dorsal depression very indistinct, marked with feeble crista superior against sulcus. Ventral furrow weak, very close to ventral rim of otolith, turning upwards and inwards anteriorly towards anterior tip of sulcus. Outer face flat to slightly convex, smooth.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDiscussion\u003c/b\u003e: \u003cem\u003eDiancistrus kasei\u003c/em\u003e represents a typical otolith pattern of the genus \u003cem\u003eDiancistrus\u003c/em\u003e characterized by a sulcus with a single colliculum, a fusiform otolith shape with a pointed anterior tip and a broader, somewhat expanded posterior tip and a smooth and convex inner face. The genus \u003cem\u003eDiancistrus\u003c/em\u003e contains many extant species (see Schwarzhans, M\u0026oslash;ller \u0026amp; Nielsen, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) in the Indo-West Pacific of which the otoliths cannot always be clearly distinguished. The otoliths of \u003cem\u003eDiancistrus kasei\u003c/em\u003e, however, are relatively easily distinguished by the combination of a very short sulcus (OL:SuL\u0026thinsp;=\u0026thinsp;2.4\u0026ndash;2.6), a low ratio OL:OH of 1.95\u0026ndash;2.0 and the rather regularly curved dorsal rim without distinct angles. Few extant \u003cem\u003eDiancistrus\u003c/em\u003e species have otoliths with similarly small sulci, in particular \u003cem\u003eD. erythraeus\u003c/em\u003e (Fowler, 1946) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eG\u0026ndash;H), \u003cem\u003eD. leisi\u003c/em\u003e Schwarzhans, M\u0026oslash;ller \u0026amp; Nielsen, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2005\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eI\u0026ndash;J) and certain specimens attributed to \u003cem\u003eD. machidai\u003c/em\u003e Schwarzhans, M\u0026oslash;ller \u0026amp; Nielsen, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2005\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eK\u0026ndash;L); the latter species is currently under review (ongoing research). The otoliths of \u003cem\u003eD. leisi\u003c/em\u003e are more elongate than those of \u003cem\u003eD. kasei\u003c/em\u003e (OL:OH\u0026thinsp;=\u0026thinsp;2.05\u0026ndash;2.1 vs. 1.95\u0026ndash;2.0) and have a distinct postdorsal angle followed by a broad indentation of the postdorsal rim. Otoliths of \u003cem\u003eD. erythraeus\u003c/em\u003e are similar to \u003cem\u003eD. kasei\u003c/em\u003e in proportions but differ in the presence of a rounded postdorsal angle followed by a small indentation of the postdorsal rim and in the broadly rounded, blunt posterior tip of the otolith. The otolith here figured from \u003cem\u003eD.\u003c/em\u003e cf. \u003cem\u003emachidai\u003c/em\u003e from off the Batanes Islands, northern Philippines, resembles closest in size and shape of the sulcus and the gently curved development of the postdorsal rim but is slightly more elongate than \u003cem\u003eD. kasei\u003c/em\u003e with a more strongly expanded posterior rim (OL:OH\u0026thinsp;=\u0026thinsp;2.1 vs. 1.95\u0026ndash;2.0). We assume that \u003cem\u003eD. kasei\u003c/em\u003e is closest related to \u003cem\u003eD\u003c/em\u003e. cf. \u003cem\u003emachidai\u003c/em\u003e from the Batanes Islands.\u003c/p\u003e \u003cp\u003eGenus \u003cem\u003eUngusurculus\u003c/em\u003e Schwarzhans \u0026amp; M\u0026oslash;ller, 2007\u003c/p\u003e \u003cp\u003e \u003cb\u003eUngusurculus phasmaticus\u003c/b\u003e \u003cb\u003en. sp. Schwarzhans, Mediodia \u0026amp; Fernando\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eM\u0026ndash;P\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eHolotype\u003c/strong\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eM\u0026ndash;N, NMP-2521, San Miguel River (locality 1), Brgy. Sibul, San Miguel, Bulacan, Tartaro Formation, Early Pliocene.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eParatypes\u003c/strong\u003e \u003cp\u003e2 specimens, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eO\u0026ndash;P, NMP-2522 and NIGSPAL-FISH-011, same data as holotype.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eName\u003c/strong\u003e \u003cp\u003eFrom phasmaticus (Latin) = hidden, difficult to see, referring to the weakly expressed differentiation into ostium and cauda.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDiagnosis\u003c/b\u003e: OL:OH\u0026thinsp;=\u0026thinsp;2.05\u0026ndash;2.15; OH:OT\u0026thinsp;=\u0026thinsp;2.3\u0026ndash;2.5. Shape elongate with pointed anterior and posterior tips. Dorsal rim flat and horizontal along long central section, with rounded predorsal and sharp postdorsal angle; pre- and postdorsal section of dorsal rim concave. Sulcus positioned asymmetrical anterior of middle of inner face, divided in weakly defined long ostial and short caudal colliculi; OL:SuL\u0026thinsp;=\u0026thinsp;1.95\u0026ndash;2.05; OCL:CCL\u0026thinsp;=\u0026thinsp;3.5\u0026ndash;3.8. Sulcus inclined at 5\u0026deg; against sulcus axis. Outer face slightly concave or flat.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eDescription\u003c/strong\u003e \u003cp\u003eSmall elongate otoliths reaching a size of about 2.15 mm in length (holotype). Anterior tip pointed, slightly supramedian; posterior tip nearly symmetrical to anterior tip but less pointed and slightly expanded. Dorsal rim flat, horizontal along about two-thirds of length, i.e., central portion; anteriorly concave above anterior tip and ascending at about 45\u0026deg; to rounded predorsal angle; posteriorly concave after sharp postdorsal angle and descending at about 35\u0026ndash;42\u0026deg; to posterior tip of otolith. Ventral rim regularly curved, deepest at about its middle. All rims smooth and sharp.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eInner face distinctly convex, relatively smooth, with slightly anteriorly shifted, moderately long, shallow sulcus filled showing a subtle distinction into a long, wide ostial colliculum and a short, narrower caudal colliculum; OCL:CCL\u0026thinsp;=\u0026thinsp;3.5\u0026ndash;3.8; OCH:CCH about 1.6. Sulcus slightly inclined against sulcus axis at 5\u0026deg;. Dorsal depression very indistinct, marked with feeble crista superior against sulcus. Ventral furrow weak, very close to ventral rim of otolith, turning upwards and inwards anteriorly towards anterior tip of sulcus. Outer face flat or slightly concave, smooth.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eDiscussion\u003c/strong\u003e \u003cp\u003eThe genus \u003cem\u003eUngusurculus\u003c/em\u003e was established based on a specialized organization of the pseudoclaspers, i.e., of a forked inner pseudoclasper. In some species, the forked inner pseudoclasper interlocks with a denticle on the proximal side of the outer pseudoclasper, forming an advanced capturing system. However, in two specimens, the forked inner pseudoclasper faces away from the outer pseudoclasper and does not interlock with a feature on the proximal side of the outer pseudoclasper (\u003cem\u003eU. philippinensis\u003c/em\u003e Schwarzhans \u0026amp; M\u0026oslash;ller, 2007, and \u003cem\u003eU. williamsi\u003c/em\u003e Schwarzhans \u0026amp; M\u0026oslash;ller, 2007). Otoliths of \u003cem\u003eUngusurculus\u003c/em\u003e are characterized by a long, flat, horizontal dorsal rim with rounded predorsal and variably developed postdorsal angles and a sulcus with a single, fused colliculum. The only exception from this pattern is \u003cem\u003eU. philippinensis\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eQ\u0026ndash;R), which shows a rounded dorsal rim and a separate, albeit very small caudal colliculum. Because of the combination of pseudoclasper and otolith patterns, \u003cem\u003eU. philippinensis\u003c/em\u003e may be considered the most primitive species in the genus. Now, \u003cem\u003eU. phasmaticus\u003c/em\u003e is intermediate in its otolith morphology between \u003cem\u003eU. philippinensis\u003c/em\u003e and the morphologically more advanced species by combining the flat, long, horizontal dorsal rim with a sulcus that shows a subtle differentiation into a longer and wider ostium and a shorter and narrower cauda, a combination which clearly distinguishes it from all other species of the genus.\u003c/p\u003e \u003c/p\u003e"},{"header":"Conclusions and Outlook","content":"\u003cp\u003eThis is the first report of otoliths found in the prolific Early Pliocene Tartaro Formation of Luzon, Philippines. It contains the first fossil record of Dinematichthyidae from the Indo-West Pacific, documenting that the genera \u003cem\u003eDiancistrus\u003c/em\u003e and \u003cem\u003eUngusurculus\u003c/em\u003e have been firmly established in the region since that time. Dinematichthyid otoliths are relatively rare in the fossil record owing to their cryptic lifestyle in reefs and on abrasive coasts, both environments that do not favor fossilization. So far, fossil dinematichthyid otoliths have been recorded since the early Oligocene of Europe (Nolf, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and the Miocene of Central America (Schwarzhans \u0026amp; Aguilera, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition, a large assemblage of otoliths will be described from this and older strata from the Philippines in further articles under preparation, which will highlight the evolution of shallow-water fish communities in the region, known to constitute the center of marine biodiversity today (Hoeksema, 2007).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of Interest and Funding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest. This study was supported by the Emerging Interdisciplinary Research (EIDR) Program \u0026ldquo;Discovering the world of first hominins in the Philippines \u0026ndash; geology, palaeoenvironment, and palaeoecology of archaic hominins in the Philippines \u0026ndash; Project 3: Geological Environments\u0026rdquo; (OVPAA-EIDR Code EIDR-C08-008) under the Office of the Vice President for Academic Affairs of the University of the Philippines to AGSF.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll materials studied, described and figured in this manuscript have been registered and deposited in public institutional scientific collections. All other data are contained in the text.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe want to extend our gratitude to the Mines and Geosciences Bureau (MGB), the National Museum of the Philippines, the National Institute of Geological Sciences, and the University of the Philippines. We cordially thank Tomoki Kase (National Science Museum, Tokyo) for generously providing rich otolith samples from the Tartaro Formation and important geographic and stratigraphic information to the sampled localities. Tomoki Kase and Steffen Kiel (Swedish Museum of Natural History, Stockholm) also kindly provided otoliths from other localities than the Tartaro Formation, which will be described in forthcoming sequences of the project. We are grateful for the support of Chien-Hsiang Lin (Biodiversity Research Center, Academia Sinica). We are also grateful to Chia-Hsin Hsu, Joeven Calvelo, John Phillip Baguio, Antero Borja II, Meyrick Tablizo, David Policarpio for their assistance during the collection and sample preparation. Meyrick U. Tablizo also kindly prepared the geological map depicted in Fig.\u0026nbsp;1. The senior author thanks Jeff M. Leis, Mark A. McGrouther and Tom Trnski (AMS), Susan L. Jewett and Jeffrey T. Williams (USNM), and Gerald R. Allen, J. Barry Hutchinson and Sue Morrison (WAM) for providing access to extracting otoliths from certain extant voucher fish specimens.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChaine, J., \u0026amp; Duvergier, J. (1934). \u0026ndash; Recherches sur les otolithes des poissons. 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(2019). \u0026ndash; Fish otoliths from the Cabarruyan Piacenzian-Gelasian fauna found in the Philippines. \u003cem\u003eZootaxa\u003c/em\u003e, \u003cem\u003e4563\u003c/em\u003e, 401\u0026ndash;443.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatanabe, T., Suzuki, A., Minobe, S., Kawashima, T., Kameo, K., Minoshima, K., Aguilar, Y. M., Wani, R., Kawahata, H., Sowa, K., Nagai, T., \u0026amp; Kase, T. (2011). \u0026ndash; Permanent El Ni\u0026ntilde;o during the Pliocene warm period not supported by coral evidence. \u003cem\u003eNature\u003c/em\u003e, \u003cem\u003e471\u003c/em\u003e(7337), 209\u0026ndash;211. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/nature09777 Captions\u003c/span\u003e\u003cspan address=\"10.1038/nature09777 Captions\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"Dinematichthyidae, otoliths, Philippines, Diancistrus, Ungusurculus, Early Pliocene","lastPublishedDoi":"10.21203/rs.3.rs-9531350/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9531350/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA large number of fossil otoliths have been collected from the Early Pliocene Tartaro Formation on Luzon, Philippines. The fauna is mainly represented by shallow-water fishes and will be described in a sequence of articles to come. Here we begin the sequence with a description of two otolith-based species of the family Dinematichthyidae (life-bearing coral brotulas, Ophidiiformes). They represent the first fossil record of the group from the Indo-West Pacific, which today forms the center of marine biodiversity for fishes and for the family Dinematichthyidae. Two new species are being described: \u003cem\u003eDiancistrus kasei\u003c/em\u003e n. sp. and \u003cem\u003eUngusurculus phasmaticus\u003c/em\u003e n. sp.\u003c/p\u003e","manuscriptTitle":"The first fossil Dinematichthyidae (life-bearing coral brotulas) from the Early Pliocene of the Tartaro Formation, Luzon, Philippines","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-15 07:40:00","doi":"10.21203/rs.3.rs-9531350/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-05-06T23:05:03+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-06T08:42:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-28T03:57:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Palaeobiodiversity and Palaeoenvironments","date":"2026-04-26T06:59:59+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":"cf4fb47a-b39d-44eb-9b66-6912eab46849","owner":[],"postedDate":"May 15th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"","date":"2026-05-06T23:05:03+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-06T08:42:21+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-15T07:40:00+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-15 07:40:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9531350","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9531350","identity":"rs-9531350","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}