PROTOCERATOPS ANDREWS IS 



is 4-3 mm. The orbits are very large (50 mm. in anteroposterior length), not surmounted by supra- 

 orbital bones or horns. The postorbitaJ squamosa] bar is narrow. Parts of the anterior and lateral 

 borders of the supratemporal fenestra as preserved indicate that the fenestra was large and that the 

 occipital roof was very delicate and not produced as far backward as in later Ceratopsia. The 

 squamosal broadly overlapped the enlarged jugal and was produced posterosuperiorly but was not 

 greatly enlarged. The pineal foramen is small or absent. The single preorbital fossae are far larger 

 than in other predentates. The premaxillae were very large and probably supported a large rostral 

 bone, which is broken off; the premaxillae and nasals approach the ceratopsian type and the same 

 is true of the pterygoids, the internal nares, and the quadrates. The quadratojugal lies on the 

 posterior surface of the quadrate. 



"The mandible has on each side a straight row of about nine relatively large and long-crowned 

 teeth, worn on their buccal sides and set far inward toward the midline. The remains of the lower 



1 



A.M.N.H. 6408 



Fig. 32. — Left lateral view of skull of Protoceratop andrezvsi, Y\ natural size, an, angular; ar, articular; c, coronoid; 

 J, dentary; /, frontal; if, preorbital fossa; iff, infratemporal fossa; /, jugal; /, lacrymal; mx, maxillary; //, nasal; nar, 

 narial opening; o, orbit; />, parietal; /■<;, palpebral ; fd, predentary; ff, parietal fenestra; pus, premaxillary ; p), post- 

 frontal (postorbital) ; pf, prefrontal; p, premaxillary teeth ; q, quadrate; qj, quadratojugal; r, rostral; sa, surangular; sq, 

 squamosal; /, teeth. 



molar crowns suggest the three-pointed lower molars of ceratopsians, rather than the spatulate, 

 many-cusped teeth of ankylosaurs and of European Acanthopholidae. The anteroposterior measure- 

 ment of the four teeth ... is 28 mm. The last tooth preserved has its tip about 13 mm. above the 

 alveolus. The first four teeth are represented by their alveoli. The diastema from the first alveolus 

 to the predentary bone was about 1+ mm. in length. The strong coronoid process rises from the den- 

 tary at a gentle slope. The predentary bone is well developed and has a pair of long inferior 

 processes, one on either side of the midline. 



"... The true Ceratopsia, [Ceratopsidae] hitherto unknown below the Upper Cretaceous of 

 America, are all far larger than Protoceratops; all of them have horns; the crest is much expanded 

 above and behind the occiput; there are epoccipital and supraorbital bones; and the orbit is small, 

 placed high up and bounded by a wide postorbital bar. The preorbital fossa is reduced to a small 

 slit. 



"As Protoceratops presents the opposite of these characters, it may prove necessary to erect for 

 it a new suborder (Protoceratopsia) but we prefer at present to regard it only as the type of a new 

 and probably primitive family, the Protoceratopsidae, characterized by the lack of horns, the very 

 large size of the orbits, and the narrowness of the postorbital-squamosal bar." 



Protoceratops skull No. 6408 A.M.N.H. (Figs. 32, 33), figured by Gregory and Mook in 1925, 

 and described as a small, young adult skull, possibly a female, may be taken as a plesiotype. Upon 

 this the following observations were made: The muzzle is deep and laterally compressed, with a well 

 developed rostral bone bearing vascular impressions. There are abundant nutritive foramina scattered 

 over the facial bones. The premaxillaries lack the sculpturing of the typical ceratopsians and form 



