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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.

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