hatcher: diplodocus (marsh) 55 



lumbar region ; in the exceedingly complicated structure of the individual vertebrae ; 

 in the marked reduction in the size and number of the teeth, and in the more re- 

 duced nature of digits III., IV., and V. in the pes. Thus while the Sauropoda in- 

 clude the more generalized of the Dinosauria, Diplodocus exhibits the greatest spe- 

 cialization attained by the different genera of this order in so far as the characters 

 of the various genera are now known. 



So little is known of the structure of many of the genera of Sauropodous Dino- 

 saurs that no attempt can at present be made to trace the phylogeny of the different 

 genera and species. Marsh has proposed six families for the Sauropoda, viz. : (1) At- 

 lantosauridse ; (2) Diplodocidse ; (3) Morosauridse ; (4) Pleurocoelidae ; (5) Titanosaur- 

 idse; (6) Cardiodontidse. The first four of these are all from the Jurassic of North 

 America, and the second and fourth (Diplodocidae and Pleurocoelidse) should prob- 

 ably be united in one family, the Diplodocidse. The Titanosauridse are from the 

 Cretaceous of India and Patagonia and may eventually prove to belong in part at 

 least to the Predentata, while the Cardiodontidse are from the Jurassic and lower 

 Cretaceous of Europe. 



The Sauropoda attained their greatest development both as regards size and 

 number, not only of individuals, but of genera and species as well, at about the close 

 of the Jurassic, while with the advent of the Cretaceous they appear to have com- 

 menced to decline, entirely disappearing toward the close of that period, where they 

 are replaced by members of the more highly specialized carnivorous Theropoda and 

 herbivorous Predentata, the remains of which occur in great abundance in the Lar- 

 amie deposits of our Western plains. 



The Species of Diplodocus. 

 Marsh has proposed two species of Diplodocus. One, Diplodocus longus, is the 

 type of the genus as well. It was first described in The American Journal of Science 

 and Arts, Vol. XVI., Nov., 1878, p. 414, and its description was based upon certain 

 vertebr£e and chevrons from the mid-caudal region. The hind limb and feet de- 

 scribed in the same publication as belonging to the same individual evidently do 

 not pertain to Diplodocus, but to Brontosaurus, and the feet of Diplodocus are now 

 known to be quite different from what Marsh had supposed thera to be in the article 

 above referred to. The caudal vertebrae and chevrons described by Marsh should 

 be taken as the type in Diplodocus longus of both genus and species. The deposit 

 from which the remains were taken was a general bone deposit or quarry, and Marsh 

 was undoubtedly led by the proximity of the limb bones and caudal vertebrge de- 

 scribed to refer them to the same individual, a very natural conclusion, but one 



