The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N Spain): biostratigraphical and paleobiogeographical implications

2025  47  22 geodiversitas Geodiversitas est une revue en flux continu publiée par les Publications scientifiques du Muséum, Paris Geodiversitas is a fast track journal published by the Museum Science Press, Paris Les Publications scientifiques du Muséum publient aussi / The Museum Science Press also publish: Adansonia, Zoosystema, Anthropozoologica, European Journal of Taxonomy, Naturae, Cryptogamie sous-sections Algologie, Bryologie, Mycologie, Comptes Rendus Palevol Diffusion – Publications scientifiques Muséum national d’Histoire naturelle CP 41 – 57 rue Cuvier F-75231 Paris cedex 05 (France) Tél. : 33 (0)1 40 79 48 05 / Fax : 33 (0)1 40 79 38 40 [email protected] / http://sciencepress.mnhn.fr © Publications scientifiques du Muséum national d’Histoire naturelle, Paris, 2025 ISSN (imprimé / print) : 1280-9659/ ISSN (électronique / electronic) : 1638-9395 Directeur De la publication / Publication director : Gilles Bloch, Président du Muséum national d’Histoire naturelle réDacteur en chef / editor-in-chief : Didier Merle assistant De réDaction / assistant editor : Emmanuel Côtez ([email protected]) Mise en page / Page layout : Emmanuel Côtez coMité scientifique / scientific board : Christine Argot (Muséum national d’Histoire naturelle, Paris) Beatrix Azanza (Museo Nacional de Ciencias Naturales, Madrid) Raymond L. Bernor (Howard University, Washington DC) Henning Blom (Uppsala University) Gaël Clément (Muséum national d’Histoire naturelle, Paris) Ted Daeschler (Academy of Natural Sciences, Philadelphie) Cédric Del Rio (Muséum national d’Histoire naturelle) Gregory D. Edgecombe (The Natural History Museum, Londres) Ursula Göhlich (Natural History Museum Vienna) Jin Meng (American Museum of Natural History, New York) Brigitte Meyer-Berthaud (CIRAD, Montpellier) Zhu Min (Chinese Academy of Sciences, Pékin) Isabelle Rouget (Muséum national d’Histoire naturelle, Paris) Sevket Sen (Muséum national d’Histoire naturelle, Paris, retraité) Stanislav Štamberg (Museum of Eastern Bohemia, Hradec Králové) Paul Taylor (The Natural History Museum, Londres, retraité) couverture / cover : Réalisée à partir des Figures de l’article/Made from the Figures of the article. Geodiversitas est indexé dans / Geodiversitas is indexed in: – Science Citation Index Expanded (SciSearch®) – ISI Alerting Services® – Current Contents® / Physical, Chemical, and Earth Sciences® – Scopus® Geodiversitas est distribué en version électronique par / Geodiversitas is distributed electronically by: – BioOne® (http://www.bioone.org) Les articles ainsi que les nouveautés nomenclaturales publiés dans Geodiversitas sont référencés par / Articles and nomenclatural novelties published in Geodiversitas are referenced by: – ZooBank® (http://zoobank.org) 749 GEODIVERSITAS • 2025 • 47 (22) © Publications scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com KEY WORDS Bivalvia, Sellaea, rudists, ammonoids, Spain, Cretaceous, Albian, Basque-Cantabrian basin, paleobiogeography, biostratigraphy. Valentin RINEAU Centre de recherche en paléontologie — Paris (CR2P UMR 7207), CNRS, MNHN, Sorbonne Université, 4 place Jussieu, F-75252 Paris (France) [email protected] Jean-Pierre MASSE Aix-Marseille Université, CEREGE, Place Victor Hugo, F-13331 Marseille cedex 03 (France) Pedro Angel FERNÁNDEZ-MENDIOLA Joanaitz PÉREZ-MALO Mikel A. LÓPEZ-HORGUE Universidad del Pais Vasco UPV/EHU, Facultad de Ciencia y Tecnología, Departamento de Geología, Sarriena s/n, Leioa, Bizkaia 48940, Basque Country (Spain) Submitted on 20 September 2024 | accepted on 20 December 2024 | published on 11 December 2025 The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N Spain): biostratigraphical and paleobiogeographical implications urn:lsid:zoobank.org:pub:C0796D42-7BB1-4F74-9063-41535B624B1E Rineau V., Masse J.-P., Fernández-Mendiola P. A., Pérez-Malo J. & López-Horgue M. A. 2025. — The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N Spain): biostratigraphical and paleobiogeographical implications. Geodiversitas 47 (22): 749-766. https://doi.org/10.5252/geodiversitas2025v47a22. http://geodiversitas.com/47/22 ABSTRACT During the Cretaceous, the gradual and extensive diversification of rudists led this group to colonise the carbonate platforms of tropical seas all over the world, structuring new ecosystems. The Albian genus Sellaea Di Stefano, 1889 has a worldwide distribution ranging from the Caribbean to Tibet, with maximum diversity centered in the Mediterranean province. This genus, recently studied in American faunas, is an important witness of the paleobiogeographical dynamics at work during this process of diversification, which generated significant endemism and helped characterise the paleobiogeographical provinces of the late Early Cretaceous. In order to add to our knowledge of this genus and the paleobiogeography of rudists, we report the existence of Sellaea in Cantabria, Spain. The middle and late Albian age is based on the presence of the ammonite Anahoplites Hyatt, 1900 and the rudists Eoradiolites jumillensis Masse, Fenerci-Masse, Vilas& Arias, 2007 and Caprina choffati Douvillé, 1898. Specimens have been identified as Sellaea stryx (Di Stefano, 1889), a species without pallial canals that belongs to the Mediterranean clade, a sister group to the American Sellaea. After describing in detail the localities where the specimens were found, we show the relevance of the presence of Sellaea stryx in the Cantabrian Albian faunas from a biostratigraphic point of view. We also discuss the impact of the presence of these faunas from a paleobiogeographical point of view. 750 GEODIVERSITAS • 2025 • 47 (22) Rineau V. et al. INTRODUCTION Rudists are a diverse group of Late Jurassic to Cretaceous bivalves that gradually spread across the carbonate platforms of warm, shallow waters (Gili & Götz 2018; Skelton 2018). The study of Cretaceous rudist diversification requires a better understanding of its biogeographical modalities, with the invasion of tropical carbonate platforms throughout the world, which generated a notable endemism (Sha et al. 2020). The Albian genus Sellaea Di Stefano, 1889 is particularly interesting for its morphoanatomy, which makes it a potential sister group to the canaliculated rudists (Skelton& Masse 1998; Rineau etal. 2020). Also, its paleogeographical distribution links the Mediterranean and American provinces. The genus Sellaea was first described from Italy, and has been subsequently recorded from Oman (Skelton& Masse 1998), Egypt (Steuber& Bachmann 2002), North America (Scott etal. 2016), and Tibet (Rao etal. 2015). It dates to the Albian, with one other occurrence from the Cenomanian of Western Europe (Orbigny 1842a; Rineau& Masse 2022). In the Middle East and the Mediterranean Tethyan domain, Sellaea was recorded from the southern margin. Its presence in Texas was first proposed by Coogan (1977), and subsequently formally described as new endemic species by Davis (1980). The presence of the genus Sellaea in North America was challenged by Skelton & Masse (1998), then fully recognized by Scott etal. (2016) and by Rineau& Masse (2022). A single species, Sellaea minuta Davis, 1980, is restricted to the Americas and is now considered as the sister group of all other Sellaea, a diverse group of at least 13species gathered in a Mediterranean clade (Rineau& Masse 2022). The diagnostic characters of the genus include a conical right valve, a coiled left valve, and two accessory cavities in the left valve, one anterior and one posterior (Rineau& Masse MOTS CLÉS Bivalvia, Sellaea, rudistes, ammonites, Espagne, Crétacé, Albien, Bassin bascocantabrique, paléobiogéographie, biostratigraphie. RÉSUMÉ Le genre de rudistes Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) dans les plateformes carbonatées albiennes de Cantabrie (Nord de l’Espagne) : implications biostratigraphiques et paléobiogéographiques. Au Crétacé, la diversification progressive et importante des rudistes va amener ce groupe à coloniser les plateformes carbonatées des mers tropicales partout sur le globe, en structurant de nouveaux écosystèmes. Le genre albien Sellaea Di Stefano, 1889 est à répartition mondiale, présent des Caraïbes au Tibet avec un maximum de diversité centré sur la marge sud de la province méditerranéenne. Ce genre, récemment étudié pour ses faunes américaines, est un témoin important de la dynamique paléobiogéographique à l’œuvre durant ce processus de diversification ayant généré un endémisme important, et qui participe à la caractérisation des provinces paléobiogéographiques de la fin du Crétacé inférieur. Afin de compléter nos connaissances sur ce genre et sur la paléobiogéographie des rudistes, nous mention nons l’existence de Sellaea en Cantabrie (Espagne) à l’Albien moyen et supérieur daté par la présence de l’ammonite Anahoplites Hyatt, 1900 et des rudistes Eoradiolites jumillensis Masse, Fenerci-Masse, Vilas& Arias, 2007 et Caprina choffati Douvillé, 1898. Les spécimens sont identifiés à l’espèce Sellaea stryx (Di Stefano, 1889), une espèce sans canaux palléaux appartenant au clade méditerranéen, groupe-frère des Sellaea américains. Après avoir décrit précisément les localités où ont été retrouvés les spécimens, nous montrons l’intérêt de la présence de Sellaea stryx dans les faunes cantabriques albiennes d’un point de vue biostratigraphique. Nous discutons également l’impact de la présence de ces faunes et des faunes associées du point de vue paléobiogéographique. 2022). The presence of canals flanking the anterior myophore of the right valve, formerly regarded as a generic character (Dechaseaux etal. 1969; Skelton& Masse 1998) was then considered by Rineau & Masse (2022) merely specific, as in Pachytraga Paquier, 1900. The inclusion of ‘Caprotina’ sensu Di Stefano (1889) into Sellaea was based on the foregoing, coupled with cladistic analysis (Rineau etal. 2020; Rineau& Masse 2022). The present paper deals with the discovery of Sellaea in the Basque-Cantabrian Basin (Northern Spain), and of its biogeographical and systematic significance. The genus is divided in two endemic clades, the first being composed of a single species, Sellaea minuta Davis, 1980, and restricted to the Americas, the second, being a diverse group of at least 13 species and known only from the Mediterranean province. Finally, we discuss potential biostratigraphic implications of this finding. GEOLOGICAL SETTING The Aptian-Albian sedimentary successions of the BasqueCantabrian Basin are traditionally referred to as the Urgonian Complex, a rock package formed in various sedimentary environments ranging from fluviatile to nearshore, shallowmarine and marine deeper-water (García-Mondéjar 1979; Rat 1988). In the province of Cantabria, in the western BasqueCantabrian Basin, differential subsidence was induced by synsedimentary tectonic activity and influenced the development of depositional highs with reduced sedimentation and lows with thick sequences (García-Mondéjar etal. 2004). Here, we highlight Albian sedimentary rocks in the Basque Cantabrian Basin that reveal previously unreported Sellaea rudist faunas in the Tethyan northern Mediterranean margin. 751 The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N. Spain) GEODIVERSITAS • 2025 • 47 (22) Specimens of Sellaea were found at two localities in the Cantabria Province in northern Spain: the Soba valley (Mazo Chico) (Fig. 1), an area of relative high subsidence rate and thick deposits, and in Suances, with very reduced overall sedimentation rates and consequent thinner record (Fig. 1). Soba valley (Mazo ChiCo) The Soba municipality lies in SE Cantabria (Fig. 1). The Sellaea rudists are located north of La Gándara village on the Mazo Chico peak. This peak lies in the Hornijo Mountain chain and includes Cretaceous rocks of the Urgonian Complex (lower Aptian-middle Albian). The W-E trending Hornijo mountain (Fig. 2A) is composed primarily of shallow marine rudist limestones and reveals small basinward-trending limestone tongues, like San Pedro and Mazos. The Mazo Chico limestone peak at an altitude of 1.100m at R: 454650 and H: 4786250 is part of the Mazos tongue (Fig. 2B). This limestone tongue progrades SE encompassing the Tejes, Mazo Chico and Mazo Grande peaks (Fig. 3). A frontal talus trends SE and additional talus margins trend toward the SW and NE (Fig. 4). The Hornijo carbonate platform is made of shallow-water limestones of the Ramales Formation. The limestones interdigitate southwards with the basinal marly Soba Formation (García-Mondéjar 1985). The transition occurs through rapid facies changes from reef-mound limestones to talus breccias and further to basinal marly facies. The rectilinear platform margin and its vertically persistent character are related to synsedimentary block-faulting and differential subsidence. Offshore banks (Aja) and a prograding barrier tongue (Mazos) are highlighted in an E-W stratigraphic cross-section (Fig. 4). The Mazos tongue is composed of shallow-water limestones 0.3km wide and 150m thick and extends 3km basinwards. The Mazos tongue cross-section reveals an internal stacking of reef-mounds (Fig. 4) and the origin of the prograding tongue is related to a sea-level lowering (García-Mondéjar 1985). The Mazo Chico limestones lithosome nucleus is massive although at both western and eastern edges bedding is recognized (Figs 4; 5). This bedding dips away from the nuclear zone (Fig. 4). The Mazo Chico limestones are made up of scattered dominantly requieniid rudists floating in micritic matrix that pass laterally to clinoformal grainier limestones (Fig. 5) and farther downflank to marls, marly limestones and sandstones that formed in adjacent slightly deeper-water marine environments (García-Mondéjar 1979, 1985). Towards the upper part of the Mazo Chico limestones, an outstanding unit is made up of a remarkable rudist assemblage composed of Sellaea (Fig. 5A). The Mazo Chico limestone unit is divided into two subunits by a silicliclastic sandstone bed that locally pinches out in the Mazo Chico SE face (Fig. 5A, B). Locally both limestone subunits are welded and the lower subunit top displays sandstone paleokarstic infills in the topmost 2metres. Fissurefilling siliclastic red mudstones (Neuweiler 1995) suggest a regressive episode with subaerial exposure. DonostiaSan Sebastián Santander Logroñ Burgos Baiona –200 m BAY OF BISCAY Paleozoic Permian-Triassic Cenozoic Keuper (diapirs) Pau –1000 m –2000 m –4000 m Gasteiz-Vitoria Aptian-Albian Main faults Bilbao B A IruñeaPamplona Jurassic-pre-Ptian –3000 m FRANCE SPAIN Upper Cretaceous MAZO CHICO SUANCES fig. 1. — Geological map of the inverted Basque-Cantabrian basin (Western Pyrenees) with the localities bearing the rudist Sellaea sp. highlighted in red. Conceptualization and drawing: Mikel A. Lopez-Horgue. 752 GEODIVERSITAS • 2025 • 47 (22) Rineau V. et al. 500 m 250 m SW NE La Sía Sequence (Upper Albian) Portillo Escalerucas Sandstones La Gandara Mound sequence Base of Carrinal sequence Cuivo Limestone Mazo Chico Anahoplites ammonite (Middle Albian, Upper part) Anahoplites ammonite (Middle Albian, Upper part) A Hornijo Platform (Aptian to Middle Albian) Mazo Grande B Mazo Chico Mazo Grande E W fig. 2. — A, Aerial view of the Hornijo carbonate platform (Aptian-Middle Albian) to the la Sía sequence (Upper Albian) stratigraphic succession; the Mazo Chico is interstratified within the grass-covered basinal marls; the average dip is 20º southwestwards; B, aerial view of the Mazos tongue (limestone ridge), composed of the Mazo Chico and Mazo Grande outcrops. The ammonites new find (Anahoplites sp.) and its lateral stratigraphic bed line (dashed) are highlighted. Conceptualization: P. A. Fernandez-Mendiola/drawing: Juan Pedro Rodríguez-López. unconformity/palaeokarst sandstone shallow-marine limestone marl /limestone breccia 500 m 75 m SE-NW Mazo Grande Mazo Chico Tejes Mortillano fig. 3. — Longitudinal stratigraphic cross-section of the Mazos limestone tongue, prograding basinwards to the southeast. Conceptualization: P. A. FernandezMendiola/drawing: Juan Pedro Rodríguez-López. 753 The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N. Spain) GEODIVERSITAS • 2025 • 47 (22) The lower subunit reaches a maximum thickness of 70metres and the upper subunit is 55metres thick and recent erosion of its top prevents maximum thickness estimates. The upper unit is dominated by beds of requieniid rudists (Pseudotoucasia santanderensis Douvillé, 1889) with a wackestone matrix, with local Chondrodonta Stanton, 1901 rudstones. Limestone beds with corals, requieniids, brachiopods and nerineid gastropods are locally observed. Near the top of Mazo Chico limestones, beds are subhorizontal (Fig. 5C). Within a succession of dominant scattered requieniid wackestones, an 8m-thick outstanding limestone package contains a dense and rich Sellaea congregation together with Horiopleura Douvillé, 1889, Eoradiolites jumillensis Masse, Fenerci-Masse, Vilas& Arias, 2007, requieniids, caprotinids, and Chondrodonta. Patchy areas of micritic matrix with scarce rudists contrast with areas of dense aggregations of Sellaea and other metazoans. A 30cm thick synsedimentary vein vertically crosscuts the micritic requieniid facies along a minimum horizontal distance of 3m and deepens for at least 20cm. The veins are filled with peloidal micrites devoid of rudists or metazoans. These veins are interpreted as synsedimentary fissures (neptunian dykes). The Mazos tongue has been interpreted as a composite carbonate mound structure based on the depositional geometry, massive character and micritic composition (Pascal& Przybyla 1989; Neuweiler 1995). The Aja limestone lithosome represents an offshore bank that is laterally equivalent to the Mazos tongue (Fig. 4). In the lower part of the Mazos limestone, scleractinian corals, Eoradiolites Douvillé, 1909, Polyconites Roulland, 1830, Arabicodium Elliott, 1957, gastropods, the sponge, Euzkadiella Mercet, 1922, and lithistid demosponges, together with in situ peloidal facies revealing stromatolite/automicrite origin are common (Neuweiler 1995). The mound flanks consist of grainstones and packstones and coral-rich limestones. A section of the southwestern Mazo Chico limestone clinoformal margin encountered coral fragments, gastropods, bryozoans, terebratulids, brachiopods, lithistid sponges, Toucasia Munier-Chalmas, 1873 like rudists, orbitolinas, Ethelia Weber-van Bosse, 1921, Lithocodium Elliott, 1956, Arabicodium Elliott, 1957 and Euzkadiella (Neuweiler 1995). The succeeding section is marly and silty with occasional talus/slope beds (breccias and megabreccias) which correlate with the topmost beds and the eroded Mazo Chico cap. The mound flanks consist of marls and slope calcareous tongues of rudist and Chondrodonta rudstones, siltstones and sandstones with ferruginous concretions, micritic limestone, siltstones, brecciated slope tongues with limestone clasts containing Eoradiolites jumillensis, requieniids, and scleractinian corals, drapped by siltstones with pyritized ammonites (cf. Anahoplites; Appendix 1). SuanCeS area Suances municipality lies on the coast of the Cantabria Province, northern Spain. Sellaea rudists are found in the nearby Punta del Dichoso headland section. This section lies about 50km northwest of Soba and 20km west of Santander (Fig. 1). The Punta del Dichoso sedimentary succession was previously described by Pascal (1985) and Najarro (2015). It is approximately 80m thick, and it is composed of five Aptian-Albian lithostratigraphic units (Fig. 6): San Esteban Formation (lower Aptian), Rodezas Formation (lower-upper Aptian), Reocín Formation (late Aptian), Barcenaciones Formation (late Albian), and the Bielva Formation (late Albian-early Cenomanian). The sedimentary record at Punta del Dichoso (80m) is significantly different than the coeval succession at Soba (3500m; Outcrop limit Shallow marine limestones Muddy limestones mounds Slope limestone breccias Intraplatform marls Shallow marine and fluvial sandstones Correlation bedding Erosional surfaces cf. Anahoplites sp. 100 m 1000 m E W Gándara mound Mazo Grande Mazo Chico Aja Hornijo Mortillano Collado del Asón Carrinal sandstones Astrana megabreccia Gándara megabreccia Belneo sandstones Cuivo Rocías San Pedro limestone tongue Fuente Fría ALBIAN lower middle upper fig. 4. — Stratigraphic framework of the Mazo Chico limestones in the the Sierra de Hornijo/valle de Soba area. In blue colour intraplatform basin trough, with carbonate mud mounds development inside it (Mazo Chico-Mazo Grande and Aja). Conceptualization: P. A. Fernandez-Mendiola/drawing: Mikel A. Lopez-Horgue. 754 GEODIVERSITAS • 2025 • 47 (22) Rineau V. et al. WE Tejes Peak Megabreccia sandstone palaeokarst clinoforms dipping west clinoforms dipping east dipping clinoforms west east 100 m Mazo Chico Sellaea Ammonites Ammonites Mazo Chico Sellaea WE Mazo Grande Hornijo carbonate platform Mazo Chico W flank marls limestone tongue Mazo Chico Sellaea (subhorizontally bedded) Mazo Chico E flank eroded out joint systems WE A B C 250 m 50 m fig. 5. — Sellaea sp. stratigraphic setting in the Mazos limestone tongue: A, two limestone units are recognized separated by an unconformity surface overlain by a sandstone; B, aerial view of the Hornijo carbonate platform in the back, and Mazo chico and Mazo Grande peaks forming the Mazos limestones unit and developing along perpendicularly to the platform margin. West of the Mazo Chico, the location of the Anahoplites ammonite is highlighted; C, Mazo Chico aerially viewed from the SE, with indication of the Sellaea outcrop in massive limestone with marked postdepositional joint systems. Western flanking beds and overlying marls are depicted. Conceptualization: P. A. Fernandez-Mendiola/drawing: Juan Pedro Rodríguez-López. 755 The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N. Spain) GEODIVERSITAS • 2025 • 47 (22) García-Mondéjar 1979). This fact is explained by Punta del Dichoso occurring in an independent structural unit (Santander Coastal Block) that underwent much less subsidence than the structural domain to which the Soba area belongs (e.g., Barnolas& Pujalte 2004). On the other hand, the Punta del Dichoso sedimentary record was deposited on a local paleohigh (i.e., Punta del Dichoso Block; PérezMalo etal. 2017), thus resulting in a condensed section with stratigraphical gaps. The rudists, Sellaea occur together with caprinids within the 13m-thick Barcenaciones Formation (Fig. 7). The unit is heterogenous (mixed carbonate-siliciclastic) and is made up of calcarenitic beds containing variable amounts of clay and/or sand. Coarse-grained and cross-bedded grainstones are interspersed in the lower and middle parts of the unit. Up-section, different types of rudists (radiolitids, requieniids, caprinids, polyconitids) and corals become especially common. Caprina choffati Douvillé, 1898 rudists occur at several stratigraphic levels, especially in the uppermost 4-5metres, where they appear together with Sellaea specimens (Fig. 7). The Barcenaciones was deposited in middle to outer platform environments (Najarro 2015). This mixed (carbonate-siliciclastic) platform fig. 6. — Stratigraphic cross section of the Aptian-Albian interval from the Escudo pass through Soba and Karrantza valleys to Sopuerta (near Bilbao) as to show the precise facies relatioships and major unconformities. Dating comes after biostratigraphical control based on ammonoids in deeper troughs and on orbitolinids in coeval shallow marine carbonate platforms (modified from García-Mondéjar et al. 2004). Mazo Chico limestones and coeval units including the Anahoplites ammonites are figured in the Soba trough. Upper Albian biozonation after López-Horgue & Owen (2004). For location of this A-B section see the Figure 1. Conceptualization: P. A. Fernandez-Mendiola/drawing: Mikel A. Lopez-Horgue. Escudo pass Estacas de Trueba pass Asón river Soba valley Karrantza valley Sopeña Sopuerta 0 km 1 2 3 4 5 6 7 8 Pondra diapir Ramales fault Alén fault Saratxaga fault Lanestosa fault Asón fault 50 km Río Miera fault Reinosa-Ebro reservoir fault Outcrop limit Aptian base Lower Aptian-upper Aptian boundary Albian base Leymeriella (L.) tardefurcata-Douvilleiceras mammillatum biozones boundary Major unconformities Lithology Shallow marine limestones Fluvial sandstones and lutites Fluvial to coastal conglomeratest and sandstones Deltaic and coastal sandstones and lutites Shallow to deep marine marls and lutites Deep marine limestone breccias, sandstones, marls and lutites Ammonite studied in this work Rudists studied in this work Carrinal sandstones Mazo Chico NEA BWESNNW SE SW 8 7 5+6 4 3 2 5+6 4 3 2 1 1 4 3 5 6 2 1 4 7 3 4 5+6 1 2 3 Lower Albian-middle Albian boundary Upper Albian base Mortoniceras (M.) fallax - M. 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Submitted on 20 September 2024; accepted on 20 December 2024; published on 11 December 2025. 765 The rudist genus Sellaea Di Stefano, 1889 (Bivalvia, Hippuritida) in the Albian carbonate platforms of Cantabria (N. Spain) GEODIVERSITAS • 2025 • 47 (22) Order AMMONOIDEA Zittel, 1884 Suborder AMMONITINA Hyatt, 1889 Superfamily hoplitoidea H. Douvillé, 1890 Family plaCentiCeratidae Hyatt, 1900 (sensu Cooper& Owen 2011) Subfamily anahoplitinae Breistroffer, 1947 (sensu Cooper& Owen 2011) cf. Anahoplites sp. Material.— A single specimen preserved as a pyritic uncrushed internal mould corresponding to a juvenile phragmocone. Despite pyrite is oxidized, suture line and overall shape are well preserved. Material deposited in the collections of the Museo de Ciencias Naturales de Álava (MCNA) with the repository number MCNA-17429. paleobiogeography.— The Anahoplitinae and Hoplitinae Douvillé, 1890 ammonites were restricted to the shallow epicontinental Albian seas of northern Europe during the (e.g., Owen etal. 2010) and characterized the European faunal province. The local occurrences of the European province anahoplitines in the study area suggests their incursion from colder areas and the opening of the seaway connections during the late middle Albian, in a basin typically Tethyan as indicated by its common ammonoid associations (e. g., Agirrezabala & López-Horgue 2017). oCCurrenCe.— Top middle Albian of Mazo Chico lutites. Valle de Soba, Cantabria, North Spain. Anahoplites occurs in the middle Albian and lower upper Albian of England and Transcaspia. In Rus - sia, Neanahoplites occurs in the middle to upper Albian transitional rossicus Zone (= upper Euhoplites lautus Subzone and Dipoloceras cristatum Zone). deSCription Oxycone shape. Involute, with outer whorl covering more than a half of flank but coiling loss involution towards the last whorl preserved. Broad and slightly convex flanks are convergent towards venter. Whorl section is compressed, and umbilical wall steep. Umbilicus equals 16% of 18.0mm diameter. Apparently smooth flanks. Narrow venter looks channeled due to loosing of the siphuncle, which is partially preserved only. Suture with shallowly bifid External lobe and narrower bifid lateral lobe. diMenSionS (in MM) D Wh Ww U 18.0 9.7 5.2 2.8 11.6 6.0 3.8 1.9 diSCuSSion The lack of preserved ornamentation such as tubercles or ribs may be due to weathering of juvenile delicate structures. However, the well-preserved suture line is indicative of only slight surficial dissolution. Accordingly, the specimen is suggested to be a nonor only slightly ornamented juvenile (Fig. S1). The general shape of the specimen, being involute, with broad convergent flanks, high whorls (Wh/Ww= 1.86) and narrow venter are features shared by the genera Anahoplites and Neanahoplites, which are only distinguishable in the middle to adult stages. Namely, Neanahoplites was erected by Cooper& Owen (2011) for the uppermost middle Albian Anahoplites with coarser and sparser ribbing (see Spath 1925, 1926; Owen etal. 2010). The suture line of the studied specimen is simpler than that of Anahoplites, being like Neanahoplites suture by the shallow incisions of the external and lateral lobes (Cooper& Owen 2011: fig.4). The specimen occurs in lutites above lower Albian carbonates and below upper Albian siliciclastics and megabreccias (García-Mondéjar& Fernández-Mendiola 1989; López-Horgue 2000; López-Horgue etal. 2009). Cooper& Owen (2011) included Anahoplites in the subfamily Anahoplitinae and Neanahoplites in Semenoviceratinae, both family Placenticeratidae. Anahoplitinae is a group that arose in the middle Albian and became extinct at the close of the Albian. Neanahoplites occurs in the topmost middle Albian N. daviesi (type species Anahoplites daviesi Spath, 1926) Subzone in Western Europe, and is derived from the longer ranging Anahoplites occurring from the base of the middle Albian to the lower upper Albian H. choffati Subzone (sensu Owen 2012; see also López-Horgue& Owen 2024). Neanahoplites forms the basal stock of Semenoviceratinae, a group of oxycones with simpler suture line than their ancestor Anahoplites, that gave rise to Placenticeratinae in the upper upper Albian (Cooper& Owen 2011). The juvenile stage of the specimen prevents more precise assignation. However, its stratigraphical occurrence and the suture simplicity points to a late middle Albian age. appenDix 1. — Ammonoid paleontology. 766 GEODIVERSITAS • 2025 • 47 (22) Rineau V. et al. appenDix 2. — Figure S1: Juvenile ammonoid from the lutites of Mazo Chico, cf. Anahoplites sp., specimen MCNA 17429 (Museo de Ciencias Naturales de Álava): A, lateral view, SEM image; B, same view highlighting the best-preserved suture lines; C, lateral view of the specimen under natural light; D, ventral view under natural light; ventral groove is a preservational artifact whereas slightly elevated ventrolateral shoulders look original. Normal light photos: Mikel A. Lopez-Horgue/ SEM photos: P. A. Fernandez-Mendiola and Juan Pedro Rodríguez-López. Preserved siphuncle Slightly elevated ventrolateral shoulders AB CD