CHAPTER 22 

 FOSSIL ANIMALS 



Many of the fundamental problems which exist in connection with 

 living organisms may also be studied, and in some degree solved, with 

 reference to beings, now extinct, which lived on the earth in times past. 

 This biology of ancient life is termed paleontology. Paleontology may 

 be defined as the science of fossil organisms. 



Fossils. — A fossil is any trace of prehistoric life. Most organisms 

 have left no trace because they were soft-bodied. Organisms mth hard 

 shells or skeletons had the best chance of being preserved, but even 

 these were screened by a fine sieve of circumstances and most were lost. 

 An animal whose bones are to be fossilized must usually be buried soon 

 after death to prevent the destructive action of oxygen, water, freezing 

 and thawing, and bacteria; and after it is seemingly safe the fossil is 

 subject to the risk of heat and pressure which would alter it beyond 

 recognition. Teeth are more likely to be preserved than bones, because 

 they are highly resistant; teeth of mastodons are often saved when the 

 bones of the same individuals have disintegrated. 



A fossil need not l^e any part of an organism. It may be only an 

 impression, a track, or even a burrow. A dinosaur walking on clay, not 

 too hard or too soft, has left its footprints to the present time. A leaf 

 leaves an imprint in the silt in which it is buried, and this impression 

 is a fossil. 



Similar objects buried only several thousand years ago are not 

 regarded as fossils; that is a matter of definition. Fortunately not 

 many objects belonging to the border line of prehistory are found, so 

 that little difficulty arises from the stipulation that a fossil be prehistoric. 



How Fossils Are Preserved. — Some animals in cold regions are pre- 

 served in the flesh. That happened to numerous woolly mammoths in 

 Siberia (Fig. 272). They fell into crevasses in the ice, were covered 

 ■with snow, and at the very low temperatures were quickly frozen. Even 

 the undigested food in their stomachs is recognizable in some of them. 

 These bodies have been frozen for probably 20,000 years. Some frozen 

 mammoths have been found in Alaska also, but only fragments of the 

 flesh were preserved. Other preservatives of flesh are oil in petroleum 

 lands (Poland, Galicia) and the acids of peat bogs. Human bodies have 

 retained their flesh, thoroughly dried and therefore resistant to bacteria, 

 in the dry southwestern parts of the United States. 



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