Abstract
The family Kentriodontidae is an extinct group of small odontocetes with a well-known fossil record in the Miocene. The Kentriodontidae diversified in the Early Miocene and reached peak diversity by the Middle Miocene. It is widely accepted that living delphinoids (Delphinidae, Phocoenidae and Monodontidae) originated from within Kentriodontidae. Despite the relatively good fossil record of kentriodontids, not much research has been done to resolve their finer cladistic relationships. Early work established a taxonomic framework for the study of the family, but the diagnostic features used are now considered symplesiomorphies. To date, no detailed cladistic study of Kentriodontidae has been performed.
This dissertation includes the first comprehensive cladistic analysis for Kentriodontidae with a data matrix (modified from Geisler’s published matrix) that includes 263 characters scored for 64 taxa. Fourteen taxa were scored as part of this study, including four previously described, two unnamed kentriodontids from USNM, and all the New Zealand species newly described in this dissertation. The results indicate that Kentriodontidae can be recognised as a family of Delphinoidea (equal weights analysis), or Delphinida (implied weights analysis), closely related to the extinct family Albireonidae and the living families Monodontidae, Phocoenidae, and Delphinidae.
The presence of Kentriodontidae in New Zealand has been mentioned in the literature and even used in molecular clock calibrations, but the material has not been formally described and named. The present study includes the anatomical descriptions of four specimens represented by Early Miocene skulls from the Early Miocene of New Zealand and one from the Oligocene-Miocene boundary. Specimen AUGD V9, new genus and species from the Te Akatea Formation of Port Waikato, is the oldest known kentriodontid, with a minimum age of 23.5 Ma.
The genus Kentriodon is represented in New Zealand by two new Early Miocene species; the first based on OU 22172 and OU 22375, and the second based on ZMT 114. Both OU 22172 and OU 22375 were collected as ‘floats’ from the Caversham Sandstone of coastal Otago, ZMT 114 was collected from the Mount Harris Formation of Kakahu, in South Canterbury. These findings expand the geographic range for the genus Kentriodon to the Southern Hemisphere. Further, the New Zealand specimens OU 22172, OU 22375, and ZMT 114 are contemporaneous with the Calvert Formation of the NE Atlantic and slightly older than the Sharktooth Hill Bonebed of the NW Pacific.
A supposed Early Miocene kentriodontid from NW Nelson, OU 22066, is an archaic odontocete more closely-related to Waipatia maerewhenua than to Kentriodontidae.
Because of the history of paleontology, there is a marked Northern Hemisphere bias in the current understanding of cetacean evolution. Exploration and research in New Zealand now offers new insights into the poorly-understood Early Miocene cetacean fauna.