278 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



inal sandstone matrix, but the greater part of the background was 

 made of a mixture of sand and cement, that when chiseled gives 

 so close an imitation of the original sandstone as to make it difficult 

 to distinguish one from the other. 



The pose of the skeleton was determined by the position of 

 the bones as originally found, and this remark applies especially 

 to the left thigh bone, which was held by the rock in its proper 

 position in the hip socket, which was directed backward at such an 

 angle as to demand a walking stride. An attempt was therefore 

 made to carry out the idea of a rapid walking motion and to make 

 the other parts of the skeleton contribute to that effect. The long 

 tail being raised clear of the ground acts as a counterpoise to balance 

 the weight and compensate for the swaying of the body and fore- 

 legs. 



The skeleton is 17 feet in length over all and about 5 feet high 

 at the hips. There have been several life restorations made by vari- 

 ous authorities; the latest done by the writer in 1915 showing his 

 conception of the animal in the flesh is shown in plate 5. 



In order to graphically present its flesh-eating habits the animal 

 was modeled completing the killing of a small herbivorous contempo- 

 rary, Camptosaurus nanus, an animal which could very well have 

 been the prey of this rapacious brute. On the other hand some 

 authorities are inclined to consider Ceratosawrus to be a reptilian 

 hyena that fed upon carrion; but, armed with teeth and claws such 

 as they have, one can hardly believe they were intended entirely in 

 the interests of peace. 



We will now turn aside from the dinosaurs and in conclusion tell 

 something about the Dimetrodon, one of the most striking and ex- 

 traordinary forms of extinct reptilian life known from the North 

 American Continent. In scientific circles this animal goes by the 

 name of Dimetrodon gigas, but is popularly known as the Giant 

 Spined Reptile, in reference to the high spines developed along the 

 median line of the back, as shown in plate 6. 



This specimen was found in northern Texas in the spring of 1917 

 by the veteran collector of fossils, Mr. Charles H. Sternberg, and 

 acquired from him for the national collections. It is the most per- 

 fect skeleton of its kind known at this time and is the first one to 

 be exhibited as a free mount, there being no less than three others 

 elsewhere mounted in bas-relief. There were many difficult mechani- 

 cal problems embodied in the mounting of a skeleton of such fragile 

 proportions, but the success of the undertaking may be best judged 

 by an examination of the photographic reproduction of the skeleton 

 here shown. An idea of the painstaking care required in fitting to- 

 gether the broken pieces of bone, cleaning off the adhering rock, re- 

 storing missing parts, and articulating and mounting the bones may 



