Skip to Main Content
Book Chapter

Origin of Mammals Based Upon Cranial Morphology of the Therapsid Suborders

By
Everett C. Olson
Everett C. Olson
Search for other works by this author on:
Published:
January 01, 1944

Serial sections of skulls of four therapsid suborders, Gorgonopsia, Therocephalia, Anomodontia, and Cynodontia, have provided a basis for detailed studies of the cranial characters of reptiles which are approaching the mammalian threshold. Structures of the inner ear, the middle ear, the occipital region, and the basicranial axis are described in detail for each of the four suborders. Comparisons of the suborders are based on analyses of proportions of the parts of the brain case and the evolution of each part of the skull is traced. These analyses are used as a basis for studies of therapsid phylogeny and the origin of the mammals. The gorgonopsians are shown to be the probable ancestors of the cynodonts and the differentiation of the gorgonopsians, therocephalians, and anomodonts is placed in pre-Tapinocephalus times.

Repeated independent development of suites of characters in the suborders is demonstrated. This leads to the conclusion that each suborder approached the mammalian threshold independently and that there are several possible sources of mammals among the therapsids. An analysis of mammalian phylogeny indicates several independent lines of mammalian development. Correlation of therapsid and mammalian phylogeny constitutes a basis for an hypothesis that three or more lines of mammals arose independently from different therapsid stocks. Tentative suggestions concerning the relationships of the therapsid and mammalian lines are considered briefly.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Origin of Mammals Based Upon Cranial Morphology of the Therapsid Suborders

Everett C. Olson
Everett C. Olson
Search for other works by this author on:
Geological Society of America
Volume
55
ISBN print:
9780813720555
Publication date:
January 01, 1944

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal