Morphology and phylogeny of Oligocene dolphins (Platanistoidea) from the Waitaki region, New Zealand

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Tanaka, Yoshihiro

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The extant South Asian river dolphin, Platanista gangetica, is one of the most highly disparate and enigmatic odontocetes. Platanista is the ultimate basis for the long-debated group Platanistoidea. There are two main historical concepts of the Platanistoidea (Chapter 1), that of Simpson (1945) for a speciose group of modern river dolphins, and that of de Muizon (1984) for a single extant species Platanista gangetica and many related fossil species. The former concept largely disagrees with molecular studies.

This project examines the two concepts of the Platanistoidea using a large morphological data set based substantially on fossils (Chapter 2). It considers the morphology, taxonomy and systematics of two new and two previously described fossil dolphins from the Kokoamu Greensand and Otekaike Limestone (late Oligocene to earliest Miocene, Waitaki region, South Island, New Zealand) (Chapter 3 to 6). Cladistic analyses show that the Waitaki dolphins are basal species of the Platanistoidea. These fossils elucidate platanistoid evolution during the little-documented Oligocene.

The redescribed Otekaikea marplesi (Chapter 3) from the Otekaike Limestone (Waitakian, 23.9 Ma) of Trig Z, represents a new genus, Otekaikea, rather than the previously-used Prosqualodon and Notocetus; O. marplesi is excluded from the Squalodelphinidae. The new species, Otekaikea n. sp. (based on OU 22306, Chapter 4) from the Otekaike Limestone (Waitakian, 24.6 to 22.3 Ma) of Hakataramea Valley, is the sister taxon to O. marplesi. Otekaikea n. sp. has single-rooted teeth, whereas O. marplesi has some double rooted teeth.

A new genus and species (based on Awamokoa tokarahi, Chapter 5) from Kokoamu Greensand/Otekaike Limestone transition, Duntroonian (25.2-25.4 Ma) is fragmentary (part skull, mandible, teeth), but has complete tympanoperiotics. The ear bones, which allow inclusion into the phylogenetic analyses, reveal Awamokoa tokarahi as a new genus basal to Otekaikea. The previously named Microcetus hectori (Chapter 6), from latest Duntroonian (around 25.2 Ma) is redescribed and transferred from the genus Microcetus to Waipatia.

These New Zealand study materials are well dated (by strontium isotopes and microfossils), and thus help to understand the stratigraphy of Oligocene Cetacea. In addition, the materials are well preserved (skulls and earbones), which expands the morphological diversity of the Platanistoidea, and improves understanding of their phylogeny, especially for the Oligocene Epoch.

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xix, 284 pages A4, some A3 foldouts

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2015Tanaka

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Abstract Only

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http://download.otagogeology.org.nz/temp/Abstracts/2015Tanaka.pdf

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Citation

Tanaka, Yoshihiro, “Morphology and phylogeny of Oligocene dolphins (Platanistoidea) from the Waitaki region, New Zealand,” Otago Geology Theses, accessed July 24, 2017, http://theses.otagogeology.org.nz/items/show/612.