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The petrosal and inner ear of Herpetocetus sp. (Mammalia: Cetacea) and their implications for the phylogeny and hearing of archaic mysticetes

Published online by Cambridge University Press:  20 May 2016

Jonathan H. Geisler  and
Zhexi Luo
Jonathan H. Geisler
Affiliation:
Department of Vertebrate Paleontology, American Museum of Natural History, New York, NY 10027
Zhexi Luo
Affiliation:
Section of Vertebrate Paleontology, Carnegie Museum of Natural History, Pittsburgh, PA 15213
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Abstract

This paper describes the petrosal (periotic) and the inner ear of Herpetocetus sp., an archaic mysticete whale (Mysticeti, Mammalia) from the Yorktown Formation (Pliocene) of North Carolina, USA. Parsimony analysis of 28 petrosal characters of Herpetocetus sp. and 11 other cetacean taxa supports the monophyly of mysticetes and the division of odontocetes and mysticetes. The in-group taxa of this analysis are: Herpetocetus, Parietobalaena, Pelocetus, Balaenidae, Eschrichtius, and Balaenopteridae. Odontocetes and the archaeocete Zygorhiza were used as successive outgroups to root phylogenetic trees and to establish character polarities. Among the modern mysticetes, the Balaenopteridae (rorquals) and the Eschrichtiidae (gray whales) are more closely related to each other than either is to the Balaenidae (bowhead and right whales). Several Miocene “cetotheriid” mysticetes and balaenids share some resemblance in the petrosal, suggesting their affinities. Quantitative information of the inner ear of Herpetocetus sp. was obtained by serial sectioning and computer graphic reconstruction. Herpetocetus sp. is much less developed than odontocetes in the cochlear structures that are crucial for high frequency hearing. Some cochlear structures in this fossil mysticete resemble more closely the non-echolocating modern mysticetes than early fossil toothed whales, indicating a possible specialization in low frequency hearing. This suggests that the archaic mysticetes of the Miocene and Pliocene did not have high frequency hearing necessary for echolocation. Herpetocetus sp. is similar to modern mysticetes but different from odontocetes in the spherical shape of the vestibule.

Type
Research Article
Information
Journal of Paleontology , Volume 70 , Issue 6 , November 1996 , pp. 1045 - 1066
Copyright
Copyright © The Paleontological Society 

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