334 STRUCTURE OF THE VERTEBRATES 



The great number of animals found demonstrates the great 

 length of time involved, and the abundance of material which 

 might have been preserved. Water living amphibia and reptiles 

 would sink into the mud. Some animals were covered by sudden 

 landslides. Animals which roamed dry regions with constantly 

 blowing sand would be buried, as illustrated by a group of 

 primitive pug-like animals, the mother and her litter being 

 almost in place. If the region were very arid the animal might 

 be mummified before being covered. A dinosaur (Trachodon) 

 has been found with the leathery skin preserved almost intact. 

 The quickest death would be falling into quicksand or deep 

 bogs of peat. A similar hazard to animal life were pits of as- 

 phalt, a particularly fine example being found in California where 

 a great mass of bones indicates that many animals became 

 mired in the sticky material and were buried. The evidence 

 shows that carnivorous animals lost their lives as they at- 

 tempted to eat others which had been caught in the thick natural 

 oil. When pits of asphalt or sinks of quicksand can be located 

 the bones of extinct animals are found enormously concentrated. 

 Another rich source is the bottom of a cave in which animals 

 lived, the packed down dung often disclosing layer after layer 

 of animal remains, giving a chronological history of life in the 

 caves. 



Fossils are frequently well preserved. It is a fallacy, en- 

 couraged by those who do not understand the methods of 

 palaeontology, that ''animals are reconstructed from a single 

 fragment". AVhen the complete skeleton of an animal is known 

 it is true that a larger bone from a similar animal indicates a 

 larger individual; but reconstructions from incomplete animals 

 are made by comparison with known species, and while minor 

 discrepancies may later come to light the method is accurate 

 and scientific. And the readiness with which the palaeontologist 

 admits any error preserves the science from bigotry and tradi- 

 tion. 



Microscopic Anatomy. The preservation of bone and wood 

 and invertebrates has been mentioned. Other structures are 

 equally well preserved as to microscopic structure. The histology 

 of fish scales is studied as accurately in fossils as in living ani- 

 mals; the joint and vertebral tendons of some dinosaurs are 



