Skip to Main Content
Skip Nav Destination

Origin of mammals based upon cranial morphology of the therapsid suborders

Everett Claire Olson
Origin of mammals based upon cranial morphology of the therapsid suborders
Special Paper - Geological Society of America (June 1944): 136 pp.


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.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Title: Origin of mammals based upon cranial morphology of the therapsid suborders
Author(s): Olson, Everett Claire
Published: 194406
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 978-0-81372-055-5
Number of pages: 136
Accession Number: 1949-012689
Categories: Vertebrate paleontology
Document Type: Serial
Bibliographic Level: Monographic
Illustration Description: illus.
Source Note: 55
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Update Code: 1949
Close Modal

or Create an Account

Close Modal
Close Modal