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.