JURASSIC PERIOD 93 



eggs. But it is very likely they were ; for such dull-witted 

 monsters can hardly have been equal to the parental duties 

 entailed by the viviparous system. If any dinosaurs brought 

 forth their young alive, such were to be found most probably 

 among the small forms. There is indeed some, though not 

 conclusive evidence that Compsognathus was a viviparous 

 creature. 



Although now quite thrown into the shade by the 

 later developments of reptile-life, semi-lizard creatures of 

 Sphenodon type abounded. And there is some evidence 

 that true lizards were in existence before the close of the LIZARDS 

 Period (Macellodus). The evidence is not undoubted ; but 

 it is highly probable that some primitive forms of those 

 creatures had by this time emerged from the Sphenodon 

 ranks. 



Crocodiles had now assumed a definite character, having CROCODILES 

 more or less lost the features which held their Triassic fore- 

 runners in close connection with dinosaurs, and lizard-like 

 animals (Tdeosauridce). They all seem, for the greater part 

 of the Period, to have been creatures with long and slender 

 snouts ; and they no doubt closely resembled the gavials 

 of our own time. They differed, however, from all croco- 

 diles now living in some important respects. The backbone- 

 vertebrae were of primitive type, being concave at both ends. 

 In the case of living crocodiles the vertebrae are convex- 

 concave, fitting into each other like ball and socket ; and 

 the backbone, therefore, has a firmer and more powerful 

 articulation. There was also greater disparity in the relative 

 lengths of the fore and hind limbs than is the case with 

 crocodiles now living. The hind-limbs were comparatively 

 long, and must have been in great requisition for swimming ; 

 whereas with living crocodiles the hind-limbs are shortened, 

 and swimming is effected almost entirely by movements of 

 the tail. These old forms, moreover, differed from living 

 crocodiles in not having their breathing passages so arranged 

 that the mouth could be kept wide open under water without 

 inconvenience. Hence, if seizing prey in their jaws, they 

 endeavoured to submerge and drown it, they ran the risk of 

 drowning themselves at the same time. There is some 



