Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Judith A. Schiebout

Abstract

All available North American specimens of squalodont whales were examined to determine species assignments, and to determine functional aspects and ecological implications. Only two existing species of the 17 referred to Squalodontidae from North America are members of that family, Squalodon atlanticus and Squalodon calvertensis. Of these two species, only S. calvertensis is based on adequate material for consideration as a valid species. Squalodon calvertensis is redescribed, based on the material which has been collected since 1923. These specimens indicate that the species is found from New Jersey to North Carolina, in the Miocene Kirkwood, Calvert, and Pungo River Formations. One specimen questionably comes from the Oligocene Old Church Formation in Virginia. A new species of squalodont, Squalodon whitmorei, is also described. This is the largest known squalodont, but it is much less common than S. calvertensis. The two species are found in the same stratigraphic units. Based on tooth shape and wear, squalodonts seem to have been opportunistic predators of fish, small mammals, and squid, like the larger modem dolphins such as the false killer whale. The weak squalodont skull structure suggests that they were not feeding on animals significantly larger than themselves, as do killer whales. The dental differences between squalodonts; and their modem analogs is probably due to the constraint in tooth form in modem species, which evolved from fish-eating ancestors which had simplified conical teeth. It appears that squalodonts exhibited sexual dimorphism both in body size and incisor morphology, reminiscent of modem beaked whales. The temporal and geographic distribution of squalodonts suggests that members of the family dispersed in the Oligocene from Tethys, to North America, and then to Europe and through Panama to Oregon. The lack of squalodonts in Japan, and their disappearance from the north Atlantic when ocean temperatures dropped in the middle Miocene, indicate that squalodonts were limited to warmer waters. Falling temperatures and a breakdown of dispersal routes with the closure of eastern Tethys, Gibraltar, and Panama made have contributed to their extinction.

ISBN

9780599213661

Pages

271

Share

COinS