444 



THE CHANGING GENERATIONS 



scendants the pythons and boas ; small slender forms appeared during the 

 Oligocene; and poisonous snakes with grooved or tubular fangs are first 

 known from the Miocene. 



One lonely survivor from the remote past deserves mention here — 

 Sphenodon, the tuatara, found only on some small islands off the New 

 Zealand coast, where through isolation it has been able to persist. It is 

 close to the type from which all the diapsid reptiles arose and preserves 

 some of the features of the ancestral cotylosaurs — in particular a rudimen- 



Fig. 28.8. The tuatara (Sphenodon punctatum) is the only surviving member of the order 

 Rhynchoeephalia, which appeared in the Permian. It is the only reptile native to New 

 Zealand, where it is now extinct except on a few small islands off the coast. Tuataras reach 

 a length of 30 inches. They live in burrows and catch their prey both on land and in the 

 water. (Courtesy American Museum of Natural History.) 



tary third eye in the top of the skull, homologous with the pineal body of 

 higher vertebrates. 



THE HISTORY OF THE ARCHOSAURS 



One of the most dramatic evolutionary histories is that of the archo- 

 saurs, or ruling reptiles, which from obscure beginnings in the Permian 

 rose to dominate the lands, the seas, and even the air during the 120 

 million years of Mesozoic time, and then disappeared abruptly from the 

 scene. The interest of this story is enhanced by the strange and monstrous 

 animals which appear in it, like the dragons and giants of a fairy tale — 

 except that these were real, and have left their bones to prove it. 



Bipedal locomotion. The ancestral cotylosaurs had short, clumsy 

 lateral legs and a slow, waddling walk. Various lines of reptiles improved 



