98 THE CERATOPSIA 



as that of an adult Monoclonius, may possibly have pertained to a full-grown Brachyceratops. \ Skull 

 with facial portion much abbreviated and deep vertically. Supraorbital horn cores small and firmly 

 united with postorbitals. Nasal horn core outgrowth from nasals, large, slightly recurved, laterally 

 compressed, and divided longitudinally by median suture. Frill with comparatively sharp median 

 crest, fenestrae apparently of small size, and entirely within the median element. Border of frill 

 scalloped but without separate marginal ossifications. Dentition as compared with Triceratops greatly 

 reduced. Five digits in the pes, the fifth being vestigial. Ilium with greatly expanded anterior 

 blade that curves strongly outward." 



The narial opening, Gilmore states, is situated "well forward and under the nasal horn." This 

 position is midway between that of the Belly River Ceratopsia and those of the Lance, for primitively 

 the horn arises over the posterior border of the nares; in the Edmonton forms, Arrhinoceratops and 

 Anchiceratops, and in the contemporary Pentaceratops, it is over the opening itself, whereas in Tri- 

 ceratops it overlies the anterior margin. This is a progressive evolutionary change which is true of 

 all phyla. 



Viewed laterally, in profile, the skull shows a great abbreviation of the facial portion, when 

 compared with the Lance genera. It is to this shortening that the generic name refers. This reduc- 

 tion of the face is also true of Chasmosaurus to an even greater degree, but there the similarity 

 between Brachyceratops and Chasmosaurus ends. The distance between the nasal horn and the 

 supraorbital horns is exceedingly short, due to the shortened nasal bones, the great fore and aft 

 development of the nasal horn, and to the forward position over the orbits of the small supraorbital 

 horns. 



"An entirely new phase of nasal horn development and one which appears to be unique among 

 dinosaurs appears in the longitudinal separation of the horn core into two halves by the nasal suture. 

 The nasal horn itself appears to be an outgrowth from the nasal bones instead of having originated 

 from a separate center of ossification, as in the more specialized Triceratops"* 1 [notably the types of 

 T. serratus and flabellatus, in each of which the sutures are well indicated and the horn ossification 

 is lost]. The Eoceratops canadensis type from the Belly River also shows a suture separating not 

 only the nasal bones, but the horn as well. There is here, however, an epinasal 42 forming the 

 anterior portion of the horn, which is lacking in Brachyceratops, according to Gilmore, although his 

 figure indicates a small, separate ossicle on the summit of the left half of the horn, with a facet 

 indicating the former presence of one on the right. Whether these are homologues of the epinasal 

 of Eoceratops, or the separate horn ossification as in Triceratops, or both, I am not sure. The latter 

 would seem probable. 



The nasal horn is directed somewhat forward, but the curve of the posterior margin gives it a 

 slightly recurved appearance. The upper half bears vascular grooves. 



The maxillaries are triangular in outline, with alveolar grooves for 20 vertical rows of teeth, 

 as compared with ±30 in Triceratops, 27 for Pentaceratops, and 35 for Monoclonius (Centrosaurus) 

 fiexus. The small number of alveoli may again be due to the juvenile character of the specimen 

 for, as the jaws elongate with growth, the teeth with their alveolar grooves would either have to 

 increase in size, which is rather doubtful, or the number of rows would increase. 



The dorsal aspect of the cranium is of interest. There is no trace of frontal bones, according 

 to Gilmore, as the pre- and post-frontals are in contact. In most reptiles the frontal is interposed 

 between them, although the condition shown in Brachyceratops is found in all the Ceratopsia except 

 Protoceratops and possibly Leptoceratops. 



The postorbital, which gives rise to the small supraorbital horn core, forms nearly one-half the 

 border of the orbit. It is separated from the postfrontal by a longitudinal suture which is elsewhere 

 unknown, even in Protoceratops. , 43 Posteriorly, it overhangs the supratemporal fossa, while ante- 



41 Gilmore, C. W., 1917, p. 8. 

 42 Lambe, L. M., 1915, p. 6, PI. V, Fig. 1. 



43 In all other Ceratopsia, the absence of this suture makes it impossible to distinguish the postorbital from the post- 

 frontal elements, hence the two terms are considered synonymous. 



