FOSSILS THEIR NATURE AND INTERPRETATION. IO/ 



bones and scales of other fishes are hard and enduring if well 

 buried under water, but are easily destroyed if left exposed in 

 contact with the atmosphere for a long 

 time. So again, while many fish and 

 reptiles and a few mammals are in- 

 habitants of the ocean, birds and most 

 mammals and many reptiles are in- 

 habitants of land, and many fish and 

 reptiles are fresh-water species only. 

 Again, the remains of Vertebrates are 

 subject to the destructive agency of 

 lower animals and of themselves, so 

 that it is not to be supposed that under 

 the most favorable natural conditions 



FIG. 28. Vertebrate. Fish. Lepidotus elvensis Blv. Jurassic. 

 a = anal fin ; c caudal fin, hemi-heterocercal ; d = dorsal 

 fin ; p pectoral fin ; r> = ventral fin ; f fulcra (on the 

 front edge of all the fins) ; k gill-covers. 



FIG. 29. Vertebrate, Amphibian. 

 Brachiosaurus ainblystomus 

 Credn. A young form (B. gra- 

 cilis Credner). Triassic. co = 

 coracoid ; _/" = femur ; fi = fibu- 

 la ; h humerus ; r = r adius ; 

 j = scapula; sr = sacral rib; / = 

 tibia; th.l = lateral and th.m 

 medial thoracic plates; u = ulna. 



FIG. 30. Vertebrate, Reptile. Ichthyosaurus quadriscissus Quenst. Jurassic. Skeleton of a 

 young individual A = coprolite. (After Steinmann and Doederlein.) 



anything more than the most meagre representation of the 

 vertebrate life of the world would be preserved in fossil con- 

 dition, and of those preserved, the more abundant would be 

 reptiles, fishes, and larger mammals, with a few birds. (Fig- 

 ures 28-32.) 



Looking over the Animal Kingdom, in this general way, 



