EUCROTAPHUS 61 



Genus EUCROTAPHUS Leidy 1850 



Eucrotaphus jacksoni Leidy 1850 



PI. I, figs. 13-15 



Original Reference: Observations on two genera of fossil Mammalia, Eucrotaphus jacksoni, and 

 Archa-othcrium mortoiii. Proc. Acad. Nat. Sci. Phila., V, pp. 90-92. 



Type Locality: Near Fort Laramie, on the North Platte River, Wyoming. 



Geologic Horizon: Upper Oligocene (upper Brule). 



Genoholotype: Cat. No. 10678 A.N.S.P., damaged cranium, extending from postorbital constriction to 

 occipital condyles. Collected by Alexander Culbertson and named in honor of Dr. Samuel Jackson, late professor 

 in the University of Pennsylvania. 



Description and Discussion: The temporal ridges unite just behind the postorbital constric- 

 tion. The sagittal crest must have been moderately long. The supraoccipital crest is entirely 

 missing. The brain case is full and rounded, and the ridge along the parietosquamosal suture is very 

 prominent. The glenoid cavity is unusually large and gently convex. The postglenoid process is 

 very large and robust. It is 13 mm. in anteroposterior diameter and 15 mm. in transverse. The 

 external auditory meatus is large, tubular, and directed upward and backward, as well as outward. 

 The bulla? are large, transversely compressed, and in posterior contact with the paroccipital process. 

 Nearly all of the latter process is broken away, only the base remaining. 



Foramina: The foramen ovale is large and well in front of the bulla. There is apparently no 

 trace of a foramen rotundttm. The foramen lacerum anterius is large, and the basicranial foramina 

 in general follow the later merycoidodont pattern. 



Dr. Leidy considered the following as the diagnostic features of this form: 



The most remarkable characteristics of this head are : — first the comparatively enormous size of the squamous 

 portion of the ossa tempora; second, the great advancement of the ossa parietalia; third, the deep groove in the 

 ossa parietalia just in advance of the squamous suture; fourth, the strength of origin of the zygoma; and fifth, 

 the form of the glenoid cavity. 



A brief review of the literature on Eucrotaphus is interesting in view of the peculiar status of 

 the genus. In 1850 Leidy proposed this generic name, "on account of the comparatively very large 

 size of the temporal bones." No special emphasis was placed on the presence of inflated bulls. 



Two months later Leidy ( 1 850B, p. 121) erected the genus Agriochcerus. The following year 

 he wrote (1851 A, p. 239): 



The fragment of cranium for which was proposed the name Eucrotaphus, from its great resemblance to that 

 of Oreodon, and its proportions, with the close alliance of Oreodon to Mcrycoidodon, Dr. Leidy suspected 

 belonged to the latter genus. 



The next year saw further doubt of the validity of Eucrotaphus when Leidy suspected that 

 Agriochcerus and Eucrotaphus were "really one and the same genus." This suspicion was expressed 

 again by Leidy (1854A, p. 56). In 1869 (p. 356) in a list of fossil forms there is no mention by 

 Leidy of Eucrotaphus, while on page 381 he placed E. jacksoni under Agriochcerus antiques and 

 E. auritus [first described by him ( 1 85+A, p. 56)] under A. major, with a question mark. 



In the last publication on this subject by the original author (1873, p. 211) is the following 

 paragraph : 



Several detached crania, differing from that of either of the species of Oreodon in the possession of large 

 ...flated ear-capsules, at first attributed to a peculiar genus with the name of Eucrotaphus, were subsequently 

 referred to Agriochcerus, which had originally been described from jaws and teeth. Later this determination 

 appeared to be confirmed by an almost complete skull in which the cranium agreed with the detached specimens. 



in 



