CHAPTER V. 



DESCRIPTION OF A NEARLY COMPLETE SKELETON OF OPHIACODON 



MARSH. 



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



The genus Ophiacodon was proposed in 1878 by the late Professor Marsh, to 

 include two new species of reptiles based upon fragmentary and disconnected 

 material collected by the late David A. Baldwin from a bone-bed near Poleo Creek 

 in Rio Arriba County, New Mexico. No distinctive characters were given for 

 the genus, nor was it possible to give such, since the two species Professor Marsh 

 described, O. mirus and 0. grandis, represent not only two distinct genera, but 

 two different orders and classes as well ; the second species belongs to the temno- 

 spondylous genus Eryops, or an allied form. The characters given in the brief 

 description of the genotype were so meager that it was impossible to identify the 

 form without comparison of the type. The genus therefore remained doubtful till 

 recently, when Williston examined the type specimens in the collections of Yale 

 University. The genotype, 0. mirus, was described by Marsh as follows: 



"A third genus of reptiles allied to the last described [Sphenacodon] is indicated by 

 various well-preserved remains from the same locality. The teeth are all carnivorous in 

 type, conical in form and all are similar. Those in the anterior part of the jaws are recurved, 

 and in general shape resemble those of serpents. The rami of the lower jaws are united by 

 cartilage. The vertebrae are veiy deeply biconcave, and even perforate, and the inter- 

 central bones are large. In the present species the teeth are nearly smooth, and somewhat 

 compressed. 



"The following measurements indicate the size of the reptile: 



"Extent of anterior sixteen teeth in dentary 75 mm. 



Extent of five lower teeth 20 



Height of crown of fourth lower tooth lo 



Depth of lower jaw at symphysis 15 



Extent of seven anterior maxillary teeth 33 



Height of crown of first maxillary tooth 9 



Antero-posterior diameter of crown 3 " 



Of the original material, only the fragmentary mandible and maxilla could 

 be positively referred to this genus and species. A study of the associated material 

 in the type collections, by a process of elimination, indicated various other parts 

 of the skeleton which might, provisionally, be associated with the genotype. The 

 greater part of this material came from a bone-bed, hereinafter designated as the 

 Baldwin Bone-bed, in which the bones were widely distributed, and almost wholly 

 disconnected. Descriptions and figures of such bones of this bone-bed as seemed 

 to be conspecific were given by Williston in his American Permian Vertebrates, 

 p. 81 , plates xxxiv-xxxvii. A comparison of these figures with those of the present 

 paper will show that most of the bones there provisionally referred to 0. mirus 

 were correctly identified, as follows: clavicle, scapula, humerus, radius, ulna, ilium, 

 femur, and tibia. The vertebra figured and described is more doubtful, since it 

 differs materially in its more elongated spine. The sacrum, very doubtfully re- 

 ferred to this genus, belongs with Sphenacodon. 



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