292 EVOLUTION AND MANKIND. 



in many df the earlier fishes. A tail was invariably present, and 

 usually two pairs of digitate limbs. Some Stegocephalians, such 

 as Branchiosaurus, were small and salamander-like. On the other 

 hand, the Labyrinthodontia, such as Mastodonsaurus, were large 

 crocodile-like creatures. These latter were so named because the 

 walls of the pulp cavity of their teeth were complicated by infold7 

 ings of dentine. The Stegocephalia were the earliest known 

 digitate animals, and their footprints are found i)reserved in the 

 coal measures and in the Karroo formation of South Africa. 

 They were fresh-water or terrestrial, and the larger ones up 1.0 

 ten feet long were predatory. 



The Amphibia attained their maximum development in the 

 late Palaeozoic and early Mesozoic times. The present-day 

 Amphibian forms, frogs and toads, are specialised. 



Present-day Reptiles are the survivors of a dying race. 

 Formerly nine orders existed ; now there are only (four. Many 

 of the extinct or Mesozoic reptiles were far more highly special- 

 ised and remarkable than any existing fonns. Different members 

 were adapted to various modes of life, the group taking full 

 possession of sea, land and air. Some of these extinct reptiles 

 may now be briefly mentioned. 



The Ichthyosaurs were great fish-lizards, with shark-like 

 heads and no neck. They were air breathers, and lived on fish. 

 The largest of them attained a length of 30 feet. 



The Plesiosaurs were long-necked sea-lizards, with small 

 heads. They became re-adapted to marine life. The later ones 

 were larger than the earlier forms, and often attained a length of 

 ten feet. 



The Dinosaurs were an enormous group of land reptiles, with 

 diversified habits. They sometimes attained a length of 80 feet, 

 and comprised the largest terrestrial and semi-aquatic reptiles 

 that ever lived. Some of them, however, had relatively small 

 heads. Stegosaurus, with its remarkable bony plates or spines 

 on the back, had an enlargement of the spinal cord in its sacral 

 region, apparently in order to control the large hinder part of 

 its body. Other forms were Iguatiodon, Bronfosauriis and 

 Triceratops. The Dinosaurs represent " the dragons of old 

 time." 



The Pterosaurs or Pterodactyls inhabited the air in the 

 Mesozoic ages. These " flying dragons " had wings well adapted 

 for flight. The wing was formed by an extension o.f the skin, 

 sup[X)rted by the arm, leg and tail, and especially l)y the greatly, 

 elongated fifth digit of the hand. It was thus more like the 

 wing of a bat than that of a bird. The size of the Pterosaurs 

 varied from that of a sparrow to that of Pferanodon. that had a 

 total wing expanse of 18 feet. Feathers were absent, and re- 

 semblances with birds were parallel or convergent. 



The Anomodontia or Theromorpha were the earliest and 

 least specialised df the extinct orders of reptiles. Thev were 

 intermediate in skeletal characters between the higliest Labvriii- 

 thodont .Amphibians and the lowest mammals. The) were terres- 



