TRICERATOPS OBTUSUS 125 



Undoubtedly, the relationship between elatus and calicorms is very close; the elongated muzzle 

 o£ cslicomis, the detailed form of the nasal horn, and the peculiar jugal of elatus seem to be about 

 the only distinguishing features, all of which may be due to individual variation. Indeed, Hatcher 

 expresses the opinion that the two species may prove to be synonymous. They certainly represent a 

 group quite apart from the frorsus-brewcornus-horridus phylum. If they prove to be of the same 

 species, the name elatus takes precedence. 



Triceratops obtusus Marsh 82 



Text Fig. 41 



Holotype: 83 No. 4720 U.S.N.M.; a nearly complete skull and jaws, except for the parietal portion of the crest. 

 Horizon: Lance formation; No. 32, and therefore, the lowermost in the sequence. 

 Locality: Niobrara County, Wyoming. 

 Collector: J. B. Hatcher, 1890. 



Hatcher could locate but little of this skull in the National Museum collections, either to figure 

 or describe in the Ceratopsia Monograph. Later, Gilmore 84 found the remaining portions, and 

 restored the skull, the unique yellow color of which made error of association virtually impossible. 



The type is an old individual with an estimated length of at least 7 feet, hence one of the 

 largest on record. The muzzle anterior to the nasal horn, however, is missing, and the length of 

 this region is subject to considerable specific variation. The nasal profile is unique among Tricera- 

 tops specimens in being convex instead of concave, although this may be due in part to crushing, 

 especially toward the rear. The dorsal contour of the crest is conjectural, but as restored by 

 Gilmore begins considerably below the level of the nasals, though rising above that level toward 

 the rear. The orbit is large, a rather elongated ellipse, the axis of which is inclined at an angle of 

 about 30° from the perpendicular. 



The descending limb of the jugal is very broad for its length, and has a marked median ridge. 

 The jugal notch is rather shallow and wide, and the infratemporal fossa very small for the size of 

 the skull, triangular in shape, with the apex toward the rear. The nasals are very broad, especially 

 over the posterior limit of the nares, and the two sides converge rapidly toward the anterior end. 

 The nasal horn is reduced to a rather broad, rounded, rugose prominence, with deep vascular 

 grooves. Laterally, the nasal profile reminds one of that of Arrhinoceratops of the Edmonton 

 formation. In the latter, however, the profile is sharp-edged, while in obtusus it is broad. 



The brow horns are very massive at their base, and have a protuberance at the rear as in elatus 

 and calicornis. But they are relatively shorter, and lack the great forward curvature of the horns of 

 these species. The horns of obtusus also resemble somewhat those of brevicomus, but they are rela- 

 tively less stocky and taper to a longer point without showing a reversed curve. 



The crest is only partly preserved, the right squamosal being entire, the left somewhat less so, 

 but nothing is present of the parietal element. There are deep vascular grooves on the dorsal 

 surface of the crest and on the under surface of the squamosal. They are not limited beneath to 

 a peripheral zone. Epoccipitals must have been present although now the margin of the squamosals 

 is smooth, without undulations. The mandible is very robust, with a low, broad coronoid, the form 

 of which has apparently been altered by crushing, as shown in the figure. The number of mandibular 

 tooth rows is 28, that of the maxillary series, which is partly broken away, cannot be determined. 

 The individual teeth are very large. 



The nearest ally of Triceratops obtusus seems to be horridus, the main distinction between them 

 lying in the nasal horn, which varies considerably among the several skulls attributed to the latter 

 species, although never to the point of obsolescence. In its loss of nasal horn and great size, obtusus 

 is specialized; otherwise, it is a generalized type. It is interesting to see the reduction of the nasal 



82 Marsh, O. C, 1898, p. 92. 



88 Gilmore, C. W., 1919, B, PI. 4. 



84 Op. cit., pp. 98-101, PI. 4. 



