CHAPTER 7 



EVOLUTION AS SEEN IN THE 



GEOLOGIC RECORD: NATURE 



OF TH E RECORD 



In earlier chapters of this book we have seen evolution 

 manifested by similarities among living animals in chemical composition, 

 structure, metabolic processes, embryonic development, and serological 

 properties of the blood. If our conclusion based on what we might term 

 circumstantial evidence is correct, in times past animals must have existed 

 that were the common ancestors from which modern animals inherited the 

 similarities revealed by morphology, physiology, embryology, and serology. 

 Can we find positive evidence that such animals actually did exist? If so 

 our accumulated circumstantial evidence will be greatly strengthened by 

 what we may regard as direct evidence. This direct evidence is supplied 

 by the geologic record. 



Fossils 



The geologic record or "record of the rocks" resembles records written 

 by man in that it must be read. Before we can read a record we must 

 learn the language in which it is written. The geologic record is written in 

 the language of fossils. Any type of remains of a prehistoric animal may be 

 considered a fossil. Accordingly, fossils take many forms. The most usual 

 type consists of petrifactions of the harder parts of the animal's body — 

 bones and teeth in the case of vertebrates, shells of molluscs, exoskeletons 



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