A dolphin fossil ear bone from the northern Neotropics–insights into habitat transitions in iniid evolution

ABSTRACT

An iniid fossil (Cetacea, Odontoceti) is reported based on a periotic found in the Codore Formation (late Miocene to middle Pliocene) of northwestern Venezuela. The marine sediments where the Codore dolphin was collected have yielded another cetacean and a diverse elasmobranch fauna. Cladistic analysis indicates a close relationship between the Codore dolphin and the extant Amazon River dolphin (Inia geoffrensis); key characteristics include a large cochlear portion that is dorsoventrally compressed and the extremely small size of the posterior process. High-resolution micro-computed tomography scans were used for the description and analysis of the bony labyrinth endocast. Geometric morphometric analysis of the bony labyrinth endocast places the Codore dolphin as intermediate between the La Plata dolphin (Pontoporia blainvillei) and Inia geoffrensis (principal component 1), but distinctive from both extant species (principal component 2). Comparisons of the depositional environment with cladistically informed reconstructions and inferences based on cochlear and vestibular anatomy suggest that the Codore dolphin had the flexibility to enter marine, brackish, and fluvial environments as some extant cetaceans do today (e.g., Pontoporia blainvillei).

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Citation for this article: Aguirre-Fernández, G., B. Mennecart, M. R. Sánchez-Villagra, R. Sánchez, and L. Costeur. 2017. A dolphin fossil ear bone from the northern Neotropics—insights into habitat transitions in iniid evolution. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1315817.

ACKNOWLEDGMENTS

We are grateful for the constructive suggestions from the reviewers R. Racicot and T. Park, and the editor O. Lambert. E. Fordyce (University of Otago) is thanked for providing useful suggestions on a draft of the manuscript. We thank C. Lefèvre (MNHN), R. C. Hulbert Jr. (FLNMH), and A. Kramarz (MACN) for kind access to collections. E. Amson (Humbodt University, Berlin) is thanked for helping with access to the Pontoporia specimens. J. Carrillo-Briceño is thanked for assistance in the field and in the laboratory. G. Schulz and B. Müller (Biomaterial Science Center, University of Basel) are thanked for greatly helping with CT scans. B. Scheffold (PIMUZ) is thanked for sharing his skills on moulding and casting. This work was supported by Swiss National Science Foundation grants 31003A_149605 to M.R.S.-V. and 200021_159854/1 to B.M. and L.C., and Fonds für Forschung und Lehre (NHMB) to G.A.F. E. Fitzgerald (Museum Victoria) and E. Fordyce (University of Otago) are thanked for providing photographs of Lipotes and Platanista used in comparisons during cladistics scoring. We thank L. Heck (Zurich) for photos of MACN-9231. We thank the Willi Hennig Society for making the cladistics software used here (TNT) freely available.