GENERAL ZOOLOGY 



Fig. 20.3. Records of ancient 

 life. A, footprints of lar^e 

 and small dinosaurs, from 

 beds of Triassic age near 

 Turner's Falls, Massachu- 

 setts; the large central print 

 measures about 4 inches in 

 length. B, Limulus trails, in 

 rock representing a Devonian 

 seashore. {A, photograph 

 courtesy Peabody Museum, 

 Yale University; B, photo- 

 graph courtesy Dr. K. E. 

 Caster.) 



Thus, the remains of extinct animal Hfe exist in a number of forms, but by 

 far the most common, and the most valuable as records of the geologic succes- 

 sion, are the stony fossils embedded in the slowly accumulated sedimentary 

 rocks. Even though the numbers of fossils seem enormous, it must be recog- 

 nized that the fossil record is tantalizingly incomplete. Although many com- 

 plete and perfectly preserved fossil skeletons have been found, the great 

 majority of fossils are merely fragments of individual animals. When pieced 

 together, they permit a fairly clear but far from perfect restoration of the 

 animal as it was in life. In addition, since the chances were small that the 

 remains of any individual organism would become fossilized, the known 



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