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

Keywords:

• Odontoceti
• systematics
• morphology
• skeleton
• evolution

Acknowledgements

Thanks go to landowner D. Pringle for access and permission to collect, and to W. and J. Simpson for accommodation and support. A. Grebneff, C. R. Samson and G. Ferguson are thanked for helping REF to collect the specimen. Thanks to O. Lambert (Institut Royal des Sciences Naturelles de Belgique) and C. S. Gutstein (Universidad de Chile) for peer review; H. Ichishima (Fukui Prefectural Dinosaur Museum) and G. Aguirre-Fernandez (University of Otago) for reviewing the draft manuscript; Te Rūnanga o Waihao Marae for comments on the proposed new taxonomic names; A. Grebneff (University of Otago) for preparing the specimen with help from C. R. Samson, S. E. White (University of Otago) for laboratory assistance; and J. Galkin (American Museum of Natural History), M. A. Reguero (Museo de La Plata), T. K. Yamada and Y. Tajima (National Museum of Nature and Science), and D. J. Bohaska, N. D. Pyenson, J. G. Mead and C. W. Potter (departments of Paleobiology and Vertebrate Zoology, respectively, Smithsonian Institution) for access to comparative specimens. Field and lab work was supported with research funds from the National Geographic Society (grant 4341-90 to REF) and the Department of Geology, University of Otago. Y. Tanaka acknowledges the University of Otago for a Publishing Bursary.