PF.NTACERATOPS FENESTRATUS 1 1 1 



Pentaceratops fenestratus Wiman r,n 



Text Fig. 40 



Cotype: (A) an almost complete skull, without lower jaw. 



Cotype: (B) Skeleton and lower jaw, without skull. 



Horizon: Kirtlaiul shales. 



Locality: 1 mile south of Kimbetoh Wash, on the south branch of Meyers Creek, San Juan County, New Mexico. 



Collector: C. H. Sternberg, 1921. 



Specimens A and B have no individual bones in common, hence it is only an assumption, but 

 highly probable, that the specimens are related. The skull of specimen A is the only element that 

 can be compared with Osborn's type of Pentaceratops stembergii, with which it agrees in all generic 

 characters. The specific distinctions mentioned by Wiman, on the other hand, are not convincing, 

 although the difference in geologic levels leads one to suppose that the two forms are distinct. 

 Wiman 's specific characters are: a fenestra present in the squamosal, and shorter and more numerous 

 epoccipitaJs. The so-called fenestra is demonstrable through the left squamosal only and seems to 

 be pathologic as it is in so many ceratopsian skulls, more often, as here, on the left side. It may be 

 either a puncture caused by a horn thrust or a bone lesion from the flesh side. (See T orosaurus 

 lotus, p. 131, Text Fig. 42.) The crest in each of the three known skulls of Pentaceratops is defec- 

 tive posteriorly but the restoration of this region in Osborn's type is based upon the separate crest 

 No. 1625 A.M.N.H. and is presumably correct. It does not seem, therefore, as though the number 

 of epoccipitals — except along the squamosal — can be accurately compared. In general proportions, 

 the two skulls are alike. The position of the broad-based horn core, with reference to the orbit in 

 fenestratus, differs from that of stembergii; in fact, it does not correspond to Osborn's generic 

 definition as it is more Triceratops-Wke. The only other contrasting detail lies in the epijugal 

 "horns" which are apparently longer in both American Museum specimens and point outward and 

 backward, while in fenestratus, which is badly crushed and sheared, they project outward and 

 slightly forward. The nasal horn seems to be longer and more slender in fenestratus. Its posi- 

 tion relative to the anterior nares is the same. 



Wiman remarks that the orbits are about the same size as the wide lower openings (infra- 

 temporal fossae) and the squamosal fenestrae. On the left side of the skull the infratemporal 

 fossa seems abnormally large as compared with that on the right. The crushing of the skull may 

 account for this. The fossa was apparently about two-thirds the size of the orbit, which is not excep- 

 tional. The parietal fenestrae are large and subtriangular, with the shorter side directed toward the 

 rear; hence, while relatively smaller, they are comparable to those of Chasmosaurus, but are larger 

 and differ in shape from the elliptical fenestrae of T orosaurus (as restored by Marsh). 



The preorbital opening ("lacrymal foramen") seems to be lacking. This is not always demon- 

 strable in ceratopsian skulls as it is a vestigial structure. It is present, however, in stembergii and 

 might be seen in fenestratus were the skull in a better state of preservation. 



The nasal horn is oval in cross-section; Wiman says this is due to the crushing of the skull and 

 that under ordinary circumstances it would be round. But I imagine that it would be oval in any 

 case, for that is the rule. The tip has disappeared, but the horn must have been moderately high. 

 It projects upward and forward but curves slightly posteriorly. A posteriorly curved nasal horn 

 and forwardly curved supraorbitals is an anomaly and seems out of reason mechanically. The only 

 other comparable instance known to me is that of a Triceratops skull, collected by Doctor Loomis in 

 the Hell Creek beds of Montana, and now in the Amherst College Museum. It is possible that in 

 both of these skulls the curve of the nasal horn is abnormal, but whether or not it is due to post- 

 mortem deformaton I cannot determine. 



The horn over the left eye is round in cross-section, while that over the right is laterally com- 

 pressed. In either case they are thicker than those of the type of P. stembergii. This, as Wiman 

 says, could be an age differentiation of the individual, or it might be a sexual character. The orbit 



58 Wiman, C, 1930. 



