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

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, <i>Crisocetus lydekkeri</i> 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 <i>C. lydekkeri</i> within the crown Odontoceti, stemward to delphinidans, ziphiids, and physeteroids. <i>Crisocetus lydekkeri</i> displays a set of characters that are shared with the members of the Squaloziphiidae family (i.e., <i>Squaloziphius emlongi</i> and <i>Yaquinacetus meadi</i>), 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 <i>C. lydekkeri</i>, <i>S. emlongi</i>, <i>Y. meadi</i>, and even <i>Dolgopolis kinchikafiforo</i>. Our phylogenetic analyses partially support the inclusion of <i>C. lydekkeri</i> within Squaloziphiidae, however this family is recovered with low support. Finally, the presence of <i>C. lydekkeri</i> and even <i>D. kinchikafiforo</i> 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.