University of Kansas Publications
Museum of Natural History
Volume 12, No. 15, pp. 657-680, 11 figs.
May 18, 1964
BY
RICHARD C. FOX
University of Kansas
Lawrence
1964
University of Kansas Publications, Museum of Natural History
Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Theodore H. Eaton, Jr.
Volume 12, No. 15, pp. 657-680, 11 figs.
Published May 18, 1964
University of Kansas
Lawrence, Kansas
PRINTED BY
HARRY (BUD) TIMBERLAKE, STATE PRINTER
TOPEKA, KANSAS
1964
30-1522
BY
RICHARD C. FOX
Information about osteological changes in the groups of reptilesthat gave rise to mammals is preserved in the fossil record, but themusculature of these reptiles has been lost forever. Nevertheless,a reasonably accurate picture of the morphology and the spatialrelationships of the muscles of many of these extinct vertebratescan be inferred by studying the scars or other marks delimiting theorigins and insertions of muscles on the skeletons of the fossils andby studying the anatomy of Recent genera. A reconstruction builtby these methods is largely speculative, especially when the fossilgroups are far removed in time, kinship and morphology fromRecent kinds, and when distortion, crushing, fragmentation andoverzealous preparation have damaged the surfaces associated withthe attachment of muscles. The frequent inadequacy of such directevidence can be partially offset by considering the mechanical demandsthat groups of muscles must meet to perform a particularmovement of a skeletal member.
Both direct anatomical evidence and inferred functional relationswere used to satisfy the purposes of the study here reportedon. The following account reports the results of my efforts to: 1,reconstruct the adductor muscles of the mandible in Captorhinusand Dimetrodon; 2, reconstruct the external adductors of the mandiblein the cynodont Thrinaxodon; and 3, learn the causes of theappearance and continued expansion of the temporal fenestraeamong the reptilian ancestors of mammals.
The osteology of these three genera is comparatively well-known.Although each of the genera is somewhat specialized, none seemsto have departed radically from its relatives that comprised theline leading to mammals.
I thank Prof. Theodore H. Eaton, Jr., for suggesting the studyhere reported on, for his perceptive criticisms regarding it, and forhis continued patience throughout my investigation. Financial assistancewas furnished by his National Science Foundation Grant(NSF-G8624) for which I am also appreciative. I thank Dr. RainerZangerl, Chief Curator of Geology, Chicago Museum of NaturalHistory, for permission to examine the specimens of Captorhinus[Pg 660]and Dimetrodon in that institution. I am grateful to Mr. RobertF. Clarke, Assistant Professor of Biology, The Kansas State TeachersCollege, Emporia, Kansas, for the opportunity to study his specimensof Captorhinus from Richard's Spur, Oklahoma. Specialacknowledgment is due M