THE ORIGIN OF MAN 59 



saurs, lived from the late Pennsylvania]! to the 

 late Triassic period. Theriodontia were reptiles 

 which lived only in South Africa during Permian 

 and Triassic times and are of great interest for 

 they indicate the probable group of reptiles that 

 gave rise to the lowest or egg-laying mammals. 

 We thus conclude the Paleozoic or ancient life 

 and shall now enter the Mesozoic or Medieval 

 life which is the age of reptiles. 



The Mesozoic Reptilia were very diversified in 

 form and adaptation. Out of these reptiles early 

 in the Triassic arose the small and insignificant 

 reptilian and egg-laying mammals, and from an- 

 other stock came the reptilian birds, with an 

 abundance of teeth. Both stocks at the close of 

 the Mesozoic era began to modernize into suck- 

 ling mammals and toothless birds respectively. 

 Of the Paleozoic amphibians the stegocephalians 

 vanished with the Triassic ; likewise the trilobites, 

 eurypterids, blastids, tetracorals and graptolites, 

 while the crinids, echinids, and brachiopods were 



