CHAPTER 9 



VERTEBRATE PALAEONTOLOGY 



The most important evidence for the theory of Evolution is that 

 obtained from the study of palaeontology. Though the study of 

 other branches of zoology such as Comparative Anatomy or 

 Embryology might lead one to suspect that animals are all inter- 

 related, it was the discovery of various fossils and their correct 

 placing in relative strata and age that provided the main factual 

 basis for the modern view of Evolution. 



It is unfortunate that the earliest rocks to contain fossils, the 

 Precambrian and Cambrian, already show representatives of all 

 the major invertebrate phyla. The earliest rocks are mainly 

 igneous and it is possible that the fossils that they once contained 

 have since been boiled away, but there is an alternative view that 

 the invertebrates suddenly and explosively evolved and had little 

 or no Precambrian history. Though there is some development of 

 the various invertebrate fossils, especially within the phyla, our 

 main examples of the evolution of the major groups of animals 

 come from our study of the vertebrates. If we ask an under- 

 graduate to give a brief account of the way in which the vertebrate 

 palaeontology provides evidence for evolution, his answer may go 

 rather like this. 



" It is possible to date the rocks fairly accurately and in general 

 the oldest rocks are at the bottom and the youngest rocks are on 

 the top. There are sometimes cases where the rocks have been 

 turned over so that the layers are sideways on or upside down, but 

 careful study soon indicates this and allows one to determine 

 their correct relative positions. If one studies the vertebrate 

 remains, one finds that there are no vertebrate fossils in the oldest 

 rocks. The next oldest rocks have some vertebrate fossils; these 

 are fragments of simple fishes. The next oldest rocks have fish 



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