A new squaloziphiid-like odontocete from the Early Miocene of Patagonia expands the cetacean diversity in the southwestern Atlantic Ocean

ABSTRACT

The Early Miocene Gaiman Formation, from Argentina, houses a taxonomic variety of odontocetes, mainly dominated by platanistoids and physeteroids. In this work, we describe a new medium-sized odontocete, Crisocetus lydekkeri gen. et sp. nov., based on a partial skull, which expands the diversity of odontocetes in the Early Miocene beds of Patagonia (Argentina). The phylogenetic analyses placed C. lydekkeri within the crown Odontoceti, stemward to delphinidans, ziphiids, and physeteroids. Crisocetus lydekkeri displays a set of characters that are shared with the members of the Squaloziphiidae family (i.e., Squaloziphius emlongi and Yaquinacetus meadi), such as a massive postglenoid process of the squamosal, ventrally longer than the posttympanic process and the exoccipital; apex of postglenoid process anteroposteriorly longer than transversely thick; presence of a deep emargination by a neck muscle fossa on the posterior end of the zygomatic process; basioccipital crests forming an angle of circa 70–90°; and a basioccipital width wider than 51% of the skull width in ventral view. Thus, we recognize a squaloziphiid-like morphology shared by C. lydekkeri, S. emlongi, Y. meadi, and even Dolgopolis kinchikafiforo. Our phylogenetic analyses partially support the inclusion of C. lydekkeri within Squaloziphiidae, however this family is recovered with low support. Finally, the presence of C. lydekkeri and even D. kinchikafiforo in the Early Miocene of Patagonia expands the paleogeographic distribution of squaloziphiid-like forms to the southwest coast of the Atlantic Ocean, suggesting that these taxa had an almost antitropical distribution.

ACKNOWLEDGMENTS

We thank E. Ruigomez for access to the collections and materials under their care. D. Pérez for his help in the interpretation of some phylogenetic results. S. Bessone for the mechanical preparation of the material. We also would like to thank O. Lambert (Royal Belgian Institute of Natural Sciences, Brussels, Belgium), S. Godfrey (Department of Paleontology, Calvert Marine Museum, Maryland, U.S.A.), and E. Fitzgerald (Geosciences Museums Victoria, Melbourne, Australia) for providing photographs of Yaquinacetus meadi that allowed anatomical comparisons between specimens. This contribution used TNT version 1.6, a program made freely available thanks to a subsidy by the Willi Hennig Society. We would like to thank the following organization for financial support: Agencia Nacional de Promoción Científica y Tecnológica (PICT 2019-00327). Finally, we thank the editors, the reviewer O. Lambert, and an anonymous reviewer whose comments greatly improved this manuscript.

AUTHOR CONTRIBUTIONS

All authors contributed equally to the conception of the study and the design of the present manuscript. In addition, all authors contributed equally to writing the description of the specimen, the results and the discussion, and to editing the entire manuscript in each round of revisions. Finally, all authors approved the final version for publication.

LIST OF SUPPLEMENTARY FILES

Supplementary File 1.docx: supplementary figures showing the complete topology of the phylogenetic results and list of the morphological characters used in the phylogenetic analyses.

Supplementary File 2.tre: all MPTs obtained under equal weight analysis.

Supplementary File 3.tre: all MPTs obtained under implied weight analysis (k = 6).

Supplementary File 4.tre: all MPTs obtained under implied weight analysis (k = 10).

Supplementary File 5.tre: all MPTs obtained under implied weight analysis (k = 74).

Supplementary File 6.nex: complete data matrix used in the phylogenetic analyses.