506 GEOLOGY OF THE DENVEE BASIN. 



would bring the foot <>t' the pubes to the ground, nearly or quite under the 

 renter of gravity of the animal. The legs and ischia would then naturally 

 aid in keeping the body balanced. Possibly this position was assumed 

 habitually by these ferocious biped reptiles in lying in wait for their prey. 



The most interesting feature in the extremities of this dinosaur is in 

 the metatarsal bones, which are completely ankylosed, as are the hones of 

 the pelvis. There are only three metatarsal elements in each foot, the first 

 and fifth having apparently disappeared entirely. The three metatarsals 

 remaining, which are the second, third, and fourth, are proportionally shorter 

 and more robust than in the other known members of the Theropoda, and 

 being firmly united to each other, they furnish the hasis for a very strong 

 hind foot. The phalanges of the hind feel are of moderate length, and most 

 of them are quite hollow. The terminal phalanges evidently supported 

 strong and sharp claws. 



The unique cervical vertebrae, the coossification of the pelvic bones, 

 and the union of the metatarsals, as in modern birds, distinguish Cerato- 

 saurus widely from all other dinosaurs, and make it the type of a well- 

 marked family, the Ceratosauridae. The nearest allied form is apparently 

 Orhithomimus, from the Laramie, recently described by the writer. 



The type specimen of Ceratosaurus was about 22 feet long when alive, 

 and 12 feet high, as restored on l'l. XXV. It was found by M. P. Felch 

 in the Atlantosaurus beds of the Upper Jurassic, near Canyon, Colo. The 

 associated fossils were mainly other dinosaurs, especially Sauropoda and 

 Ornithopoda, together with various small mammals. 



OTHER VERTEBRATES. 



In addition to the dinosaurs here described, many other reptiles lived 

 in this region during Jurassic time, and not a few left their remains in the 

 deposits now known as the Atlantosaurus beds. Among- these were various 

 crocodiles of modi-rate size, and some nearly as large as existing species. 

 The genera appear to he distinct from those now living. One of the most 

 interesting i> Diplosaurus, the type specimen of which, found at Morrison in 

 1887, is represented in the diagram, tig. 62, on the opposite page. All these 

 crocodilians had biconcave vertebras, and also seem to have been protected 

 by a dermal covering of bony plates, as in existing species. 



