GREAT STEPS IN ORGANIC EVOLUTION 833 



certainly exhibited. The connection may be that long hind legs help 

 in rapid locomotion, as is well illustrated by the Collared Lizard of 

 Australia, Chlamydosaurus, which seems to be at present achieving 

 considerable success as a swiftly moving biped. As many of the 

 Dinosaurs were carnivores, it is also possible that the bipedal habit 

 was associated with the specialisation of the fore-limbs for capturing 

 prey. 



Of the Triassic times, when Dinosaurs had become firmly estab- 

 lished, it may be said that arid conditions continued over immense 



Fig. 143. 



The Australian Collared Lizard, Chlamydosaurus. After Sa villa Kent. This 

 reptile is essaying a bipedal mode of progression. 



areas. In the Jurassic there was an oscillation to humidity, and 

 many of the Dinosaurs, sometimes toothless, often huge and sluggish, 

 fed on the rich vegetation around the swampy shores of shallow 

 seas. Towards the close of the Jurassic there seems to have been 

 another great uplift, probably imposing a check on some of the 

 Dinosaur types, but in the Cretaceous times there were again exten- 

 sive amphibious habitats, and the Dinosaurs reached their climax of 

 size, success and specialisation — the last probably continued beyond 

 the limit of safety. For the end came suddenly, as geologists count 

 sudden, and no member of all the hosts of Dinosaurs survived the 

 close of the Cretaceous. The causes of their extinction are uncertain, 



VOL. II H 



