A MOUNTED SKELETON OF DIMETRODON GIGAS IN THE 

 UNITED STATES NATIONAL MUSEUM, WITH NOTES ON 

 THE SKELETAL ANATOMY. 



By Charles W. Gilmore, 



Associate Curator, Division of Paleontology, United States National Museum. 



INTRODUCTION. 



During the spring of 1917 the United States National Museum ac- 

 quired from Mr. C. H. Sternberg, a small collection of vertebrate 

 fossils, which he and his son Levi had made earlier in the season from 

 the Permian formation as exposed in the vicinity of Seymour, Baylor 

 County, Texas. 



The collection consists of a very fine skeleton of Dimetrodon gigas 

 Cope, several hmidred bones of the smaller species of Dimetrodon, 

 and between 35 and 40 skulls and partial skeletons of the smaller 

 reptilian and batrachian forms that comprise this interesting fauna. 



The greater part of the collection was obtained from a deposit of 

 bones on the Craddock ranch, discovered in 1909 by members of an 

 expedition from the University of Chicago. In writing of this dis- 

 covery. Doctor WiUiston ^ designated it as the "Craddock Bone 

 Bed," and I quote below from his remarks on the manner of occur- 

 rence of the fossils found there. 



The bones in tliis deposit extend through a thickness of about 1 foot over a con- 

 siderable space, a few hundred square feet, imbedded in red clay like that of the 

 Cacops bed. They are unlike those of the Cacops bed, however, for the most part 

 isolated and generally more or less free from incrusting matrix, and usually in the 

 most perfect preservation. Not a few, however, show effects of erosion, as though they 

 had been rolled upon a beach of hard, shallow bottom. 



The skeleton of Dimetrodon gigas, as so often happens in deposits 

 of fossil bones, was the one exception to the general conditions pre- 

 vailing there in that considerable portions of the skeleton were 

 found articulated, and the association of these articulated and other 

 parts as pertainuig to a single individual was further indicated by an 

 adhering matrix which cemented them together into compact masses. 

 For example, the skull was found disarticulated, but its separate ele- 

 ments with the jaws were bound into one mass by the enclosing 



1 Williston, S. W., American Permian Vertebrates, pp. 5-7, 1911. 



Proceedings U. S, National Museum, Vol. 56— No. 2300. 



525 



