Awamokoa tokarahi, a new basal dolphin in the Platanistoidea (late Oligocene, New Zealand)

Abstract

A late Oligocene marine dolphin – Awamokoa tokarahi gen. et sp. nov. – from the Kokoamu Greensand (Duntroonian stage, 25.2–27.3 Ma) of Tokarahi, North Otago, New Zealand, is a representative of the clade Platanistoidea. The single known specimen preserves a fragmentary skull, well-preserved tympanoperiotics (ear bones) and several postcranial elements. The fossil helps to trace platanistoid history from its oceanic origins to the endangered living South Asian river dolphins. The morphologies of the temporal fossa and mandible suggest that Awamokoa and other more basal platanistoids (Waipatia) were probably macroraptorial feeders with a strong bite. In contrast, later-diverging fossil platanistoids (Huaridelphis + Squalodelphis + Zarhachis) and the modern Platanista gangetica, which display longer rostra and increased numbers of nearly homodont teeth, probably had/has a faster but weaker bite, with less processing of food than the basal platanistoids. Otekaikea and Notocetus show intermediate jaw structure. Long-term shape changes in the periotic (earbone) involve the pars cochlearis (thinner in later taxa) and changes in vascular sulci (less pronounced in later taxa), but the exact functional significance is uncertain.http://zoobank.org/urn:lsid:zoobank.org:pub:79CC0BCE-4ED5-425F-897B-F6EBEFC159CA