6 THE COLLECTION OF FOSSIL VERTEBRATES 



tions of man are not found, and the remains of lower ani- 

 mals which they contain are unlike any now living — the more 

 unlike as the rock is more ancient. These remains are called 

 fossils. They consist only of the hard parts of animals (bones, 

 shells, spines etc.). The soft parts are never preserved, and 

 only very rarely is some trace of skin or hair, horns or hoofs, to 

 be distinguished. As in the course of ages the mud or sand in 

 which they are buried changes to rock, so little by little the 

 fossils have been changed by heat, pressure and especially by 

 the slow infiltration of mineralized waters into brittle, stony 

 material, while retaining their outward form and usually their 

 peculiar structure. But mud and clay, in changing into rock, 

 settle down and contract considerably, and the fossils are flat- 

 tened out correspondingly, sometimes to such a degree, in the 

 case of a rock which has once been a soft, oozy mud, that they 

 suggest rather a picture or a bas-relief than the original form 

 of the animal. The fossil skeletons of marine reptiles and fishes 

 on the walls of the corridor hall and in the case opposite the 

 elevator have been flattened out in this manner, especially the 

 Ichthyosaur skeletons. 



From fossils we can interpret the history of the world of life 

 during the long ages before man appeared. The science which 

 Science of deals with the ancient history and evolution of the 

 Palaeon- animal kingdom is Palaeontology {TiaXaiu?, ancient, 

 tology. ovra, living beings, -Xoyta, science). It tells us of a 

 long period of time before Man appeared, probably millions of 

 years, during which Mammals of great size and unfamiliar form 

 were the dominant animals — of a yet longer era before that, 

 during which huge Reptiles were rulers of earth, sea and air — 

 and of other still more ancient periods during which Amphibians, 

 Fish and Invertebrate Animals held sway in turn. \'ertebrate 

 Palaeontology deals only with the higher classes of fossil animals, 

 the Vertebrata, or those that have backbones (fish, am]ihibians, 

 reptiles, l)irds and mammals). 



Earth-history or geological time lias been ilix'idcd into many 

 Geological p'lrts according to the evidence furnished by the rocks 

 Time. and the fossils contained therein. The iirinci]ial sub- 



divisions are shown in the accompanying table : 



