420 DINOSAURIA CHAP. 



functional teeth themselves are implanted in sockets. The 

 generic name refers to the peculiar chevron-bones, each half of 

 which diverges into an anterior and a posterior branch. 



It is difficult to understand how these huge, long-necked 

 Sauropoda lived and moved about. The long neck suggests at 

 first sight predacious habits, but the teeth, rather feeble in 

 Diplodocus, and distinctly of the plant-cutting type in other 

 genera, put this out of the question. The high position of the 

 unpaired nasal opening, and the shortened nasal bones of 

 Diplodocus, are features indicative of aquatic habits, but the 

 short-toed, plantigrade limbs are absolutely adapted to terrestrial 

 life, and we cannot well assume that such enormous brutes as 

 Atlantosaurus could possibly have ventured into swampy ground. 



Order II. THEROPODA. 



Pubes simple, with symphysis. Premaxillae ivith teeth. 

 Digitigrade. Carnivorous. 



The teeth are pointed, recurved, laterally compressed and 

 serrated. The nasal openings are large, lateral, and nearly 

 terminal. The vertebrae and the large bones of the limbs are 

 hollow. The fore-limbs are .considerably shorter than the hind- 

 limbs, which are distinctly digitigrade, many of the species 

 having a pronouncedly upright gait. The proximal tarsalia 

 show a tendency to fuse with the tibia, and the astragalus 

 has sometimes an ascending process, by which the fusion with 

 the tibia is strengthened. The first and fifth metatarsals are 

 often reduced, while the three middle bones are elongated and 

 sometimes even fused with each other, so that the whole foot 

 assumes a striking resemblance to that of birds. The ter- 

 minal phalanges are protected by curved claws. Owing to 

 the shortness of the fore-limbs, and the often considerable 

 length of the hind-limbs, which are strongly bent at the knee 

 and the ankle-joint, these animals must have progressed some- 

 what like clumsy kangaroos. 



The Theropoda, of which a great number of genera are now 

 known, from the size of a slender cat to that of an elephant, 

 lived from the Upper Trias to the Upper Oolite, both in Europe 

 and in North America. 



Brontozoum giganteum, one of the oldest forms, is known 



