494 GEOLOGY OF THE DENVER BASIN. 



RESTORATION (.11' UKIINTI'.S.U HI'S. 



In the restoration given on PI. XXI the diminutive head will first 

 attract attention, as it is smaller in proportion to the body than in any 

 vertebrate hitherto known. The entire skull is less in diameter or actual 

 weight than the fourth or fifth cervical vertebra. 



A careful estimate of the size of Brontosaurus, as here restored, shows 

 that when living the animal must have weighed more than 20 tons. The 

 very small head and brain, and slender neural cord, indicate a stupid, 

 slow-moving reptile. The beast was wholly without offensive or defensive 

 weapons, or dermal armature. 



In habits Brontosaurus was more or less amphibious, and its food was 

 probably aquatic plants or other succulent vegetation. The remains are 

 usually found in localities where the animals had evidently become mired. 



The present genus, Brontosaurus, together with the genera Atlanto- 

 saurus, Apatosaurus, and Barosaurus, form a distinct family of the 

 Sauropoda, which the writer has called the Atlantosauridse. 



liiPLimiici's. 



In the same horizon in the Denver Basin remains of another peculiar 

 genus, Diplodocus, are quite abundant, especially the teeth. This genus, 

 described by the writer in 1884, represents a distinct family of the 

 Sauropoda, and one of much interest. The skull and nearly every part of 

 the skeleton are now known. The type specimen was found by M. 1'. 

 Felch, near Canyon, Colo. Other remains of the same genus have been 

 found near Lake Como, in Wyoming. 



The skull of Diplodocus is of moderate size. The posterior region is 

 elevated and narrow. The facial portion is elongate, and the anterior 

 part expanded transversely. The nasal opening is at the apex of the 

 cranium, which from this point slopes backward to the occiput. In front 

 of this aperture the elongated lace slopes gradually downward to the end 

 of the muzzle, as represented in fig. 44. 



Seen from the side, the skull of Diplodocus shows five openings: A 

 small oval aperture in front, a large antorbital vacuity, the nasal aperture, 



