HALLOPUS, BAPTANODON, ATLANTOSAURUS BEDS 345 



hind limbs] and in some other respects. Portions of one Wealden animal, referred 

 by Mantell to Pelorosaurus, are certainly very similar to some of the smaller 

 forms of Morosaurus, especially in the proportion of the fore and hind limbs, 

 which are unusually short. This fact would at once distinguish them from 

 Pelorosaurus, and, until the skull and more of the skeleton are known, they 

 cannot be separated from Morosaurus. 1 



It is quite true that the Brachiosauridae of Riggs (Brachiosaurus 

 Riggs and Haplocanthosaurus Hatcher) have a more generalized 

 structure in this respect than has Cetiosaurus even, but we have no 

 reason to assume that all the generalized forms died out with the 

 advent of specialized ones, such as are most of the American Sauro- 

 poda. Nor do I think it quite certain that the Brachiosauridae are 

 the most generalized, certainly not if the hypothesis that the Sauro- 

 poda have been derived from primitive ornithopoda is at all probable. 

 Furthermore, the genus Pleurocoelus, originally described from the 

 Potomac beds, has been recognized in the Atlantosaurus beds by 

 Marsh, and later by Hatcher, and forms from the Wealden have 

 been referred, provisionally at least, to the same genus. 



For the most part, the carnivorous dinosaurs have little value in 

 the correlation of the horizons. Megalosaurus is reported from 

 Europe from the Lias to the Wealden. In America we have three 

 or four genera of the Megalosauridae in the Atlantosaurus beds, 

 Creosaurus, Allosaurus, Antrodemus, and Ceratosaurus, and the 

 family survived to the Laramie Cretaceous. Coelurus was described 

 from the Atlantosaurus beds, but is known to occur in the Potomac 

 beds. In the Wealden of England Aristosuchus is very closely allied, 

 indeed is supposed to be identical, and all the other genera referred 

 to the Coeluridae are from the Wealden. In the extensive hollowness 

 of the bones of the skeleton, Coelurus is not only the most specialized 

 of dinosaurs, but of all vertebrate animals. The evidence then 

 to be derived from the Theropoda is for the contemporaneity of the 

 Wealden with the Atlantosaurus beds. 



So far from the evidence of the Iguanodontia being against this 

 correlation, I believe that it is decidedly for the identity of the two 

 horizons. Iguanodonts are found in abundance in the Atlantosaurus 

 beds, and of the largest size and high specialization. Speaking of 

 them, Marsh has said: 



1 Dinosaurs of North America, p. 184. 



