A new species of the large delphinidan genus Miminiacetus from the Middle Miocene of Peru

In the East Pisco Basin (southern coast of Peru), the rich fossil record of cetaceans from the Pisco Formation is currently mainly concentrated in the Upper Miocene sequences P1 and P2. While some progress has recently been made in the study of the palaeobiological content of the Middle Miocene sequence P0, more work is needed to assess cetacean diversity in this unit and to analyse related palaeobiogeographical patterns. Based on a new skull including the cranium, ear bones, mandible, and teeth from the East Pisco Basin locality of Mal Paso, we describe a new large delphinidan species from the P0 sequence. Sharing strong morphological similarities with Miminiacetus pappus, from the Middle Miocene Calvert Formation (Maryland, USA), the new species is placed in the same genus and named Miminiacetus barrancai sp. nov. While it differs from M. pappus in, among others, its larger size and lower mandibular tooth count, the sister-group relationship recovered in our phylogenetic analyses points to an antitropical distribution for the genus Miminiacetus. This new record strengthens the cetacean faunal link between P0 and the Middle Miocene strata of the Calvert Formation. Miminiacetus spp. share several cranial and mandibular features with the modern beluga Delphinapterus leucas, possibly indicating some degree of specialization towards suction feeding in this large dolphin. Furthermore, the unusual occlusal wear on teeth of Miminiacetus spp. is reminiscent of the condition in D. leucas (in which it is related to alignment of upper and lower teeth) and is possibly linked to a jaw-clapping behaviour.https://zoobank.org/urn:lsid:zoobank.org:pub:400D3B92-2C85-494A-B0D3-F6F5338D5430