The Paleogene crocodyliform record is rich in taxonomic diversity, preserving crown and stemeusuchians alongside late-surviving neosuchians and notosuchians. This richness is mainly known from the extratropical latitudes of the New World and Eurasia, contrasting a poorly sampled tropical record. Within the tropics, the Paleogene of low-latitude southeast Asia is comparatively undersampled, with the Eocene Krabi Formation of Thailand representing the southernmost fauna. This crocodyliform fauna is composed of orientalosuchins and gavialoids, consistent with more northern records from southern Asia. Here we describe the first crocodyliform fossils from the Eocene of Indonesia, collected from the middle-late Eocene Talawi Member of the Sawahlunto Formation, west Sumatra. The Talawi Member represents a coastal swamp environment, preserving invertebrates, fish, and turtles along with rare frog, snake, and mammal fossils. Recovered crocodyliform fossils are often isolated and disarticulated, consisting of cranial remains including a partial braincase and jaw fragments, as well as relatively abundant teeth and osteoderms, vertebrae, and at least two autopodial elements. Procoelous vertebrae indicate eusuchian affinities. Osteoderms are diverse, with keeled and keelless squared and subrectangular forms. High and low-crowned fluted tooth morphotypes compare favorably to coeval gavialoids and orientalosuchins. A ziphodont form is present, potentially a planocraniid or sebecosuchian. External morphology of the braincase, such as narrow basioccipital tubera, a basioccipital plate bearing a crest, and a large basisphenoid exposure suggest a non-gavialoid identity. This is supported by preliminary observations of highresolution microCT scans, which imply a lateral carotid foramen ventral to the metotic foramen and laterally aligned medial and lateral eustachian foramina. The Sawahlunto fauna extends the southernmost geographical range of the Eocene southeast Asian crocodyliform fauna and represents the first multitaxon crocodyliform fauna from equatorial Asia. The ziphodont teeth either represent the last-occurring Asian planocraniids in a tropical refugium, or an incursion of Gondwanan sebecosuchians from India into the Asian tropics.
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In 1909, the famous palaeontologist Louis Dollo announced, in a paper about the Belgian fossil vertebrates, a new Oligocene (Rupelian) genus and species of sea turtle, ‘Oligochelone rupeliensis’. He indicated that it was established for a specimen that preserved the complete carapace and several appendicular bones, being characterized as “a typical marine turtle”. No further information, but neither photographs or drawings, were provided by him. He planned to publish the study of this species in the future, but this did not happen. Only a schematic drawing of the plastron of that specimen, as well as a photograph of a tibia attributed to this taxon without justification, were presented, by another author, seventy years later. The first-hand study of the specimen considered by Dollo allows us to observe that it does not preserve any tibia, so that attribution cannot be supported. Therefore, except for that imprecise drawing of the plastron published more than four decades ago, no additional information was available so far. In fact, ‘Oligochelone rupeliensis’ was recognized as a nomen nudum. After a preliminary analysis of the specimen considered by Dollo, one of us (APG) and other collaborators recently indicated, without justification, that, although ‘Oligochelone rupeliensis’ could be closely related to the Eochelone representatives, it differs from all defined members of Cheloniidae. Therefore, we point out that a detailed anatomical study of this form, as well as its comparison with other species, would be necessary to propose, for the first time, a diagnosis, if its specific validity can be confirmed. Taking this into account, that partial skeleton has been analyzed in detail by us. To improve the comparative framework, both the type material and additional individuals from all Eocene and Oligocene cheloniid taxa recognized for the Belgian record have also been analyzed first-hand. The preliminary results are presented here.
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