CHAPTER VI. 



A DESCRIPTION OF CERTAIN COLLECTIONS OF BONES REFERRED TO 



SPHENACODON MARSH. 



By E. C. Case and S. W. Williston. 

 Sphenacodon feroz Marsh. 



Marsh, Am. Jnl. Sc, vol. xv, 1878, p. 410. 

 Baur and Case, Trans. Am. Phil. Soc, vol. xx, 1894, p. 4. 

 Case, Publication No. 55, Cam. Inst. Wash., 1907, p. 67. 

 WiUiston, American Permian Vertebrates, 191 1, p. 78. 



Marsh's original description of this genus is as follows : 



"In the present genus the anterior teeth are somewhat like those of the reptile described 

 above, but the posterior, or more characteristic ones, are totally different. The crowns 

 are much compressed, and have very sharp cutting edges without crenulations. In the 

 present species the carnivorous teeth are crowded together, and the crowns placed sHghtly 

 oblique, and twisted. The jaws were comparatively short and massive. The rami of the 

 lower jaws were apparently united by cartilage only, and the symphysis was short. The 

 vertebrae are deeply biconcave. 



"Measurements from the type of this species are as follows: 



" Length of the dentary bone 150 mm. 



Space occupied by the teeth 130 



Extent of four anterior caniniform teeth 25 



Extent of twenty compressed teeth 105 



Height above jaw of second lower tooth 15 



Depth of dentary bone at symphysis 26 



Height of crown of compressed tooth 8 



- Transverse diameter 4 



"This reptile was about 6 feet in length, and carnivorous in habit. Its remains are from 

 the same locahty in New Mexico that yielded those of Noihodon." 



Marsh made no attempt to classify this animal further than to remark on its 

 carnivorous habits. Baur and Case regarded it as belonging to the Clepsydrop- 

 sidse, and Case compared it directly with Dimetrodon. These conclusions were 

 drawn from the imperfect lower jaw which forms the holotype of the genus and 

 species. Williston assembled much more material in the Yale collection, and 

 associated several bones which he regarded as doubtfully belonging with the genus ; 

 he also was unable to distinguish the genus positively from Dimetrodon. The 

 collections made by the expedition to New Mexico in the summer of 191 1 added 

 much new material, but more decisive information as to the characters of the 

 genus has been obtained from the Yale collections, which have been further worked 

 out since the time of Williston's studies in 1910, and which have been attentively 

 studied by him the present season. The material obtained by the Chicago-Michigan 

 expedition may be described as follows: 



This material consists of three lots of bones found in close association, together 

 with ntmierous isolated bones, all from the banks of Poleo Creek in Rio Arriba 

 Cormty, New Mexico. The associated lots are : 



First, ten dorsal vertebrae, eight of which are matrically connected, five of 

 them with spines; and a separate coracoid. From the Miller quarry. 



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