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CHAPTER XLV 



PALEONTOLOGY 

 (By W. M. Winton, Texas Christian University) 



Paleontology deals with fossils. One of the most difficult biological 

 concepts to define satisfactorily is the term fossil. Broadly speaking, 

 the word should refer to records left by organisms and not by non- 

 vital forces. Expressions such as "fossil ripple marks," "fossil sand 

 dunes" and the like should never be used. 



On the other hand, any recognizable trace left by an ancient or- 

 ganism is a fossil. Bones and shells, of course ; but also scales, plates, 

 impressions, burrows, leaf prints, intestinal droppings or coprolites, 

 all are fossils. 



Among the most interesting fossils are tracks. The poet's "foot- 

 prints on the sands of time" in Triassic valleys of New England, 

 the "thunderbird dance floors" of the Navajo reservation, and the 

 huge tracks around Glenrose, Hamilton, and Hondo, Texas, are all 

 dinosaur tracks. Abundant as are skeletons of Mesozoic dinosaurs, 

 many are known only by their footprints hardened in the shores of 

 ancient seas. 



Other indirect records may be of considerable biological importance. 

 In the deposits of the Lower Cretaceous division of Texas a few ex- 

 amples of the extinct oyster, Exogyra, have been found which exhibit 

 pearls. These pearls (the best specimen is in the Museum of the Bu- 

 reau of Economic Geology) are of the kind known as body pearls. A 

 quarter of a century of research by the Marquesan commissions of the 

 French Government has shown us that pearls of this kind are 

 caused only by parasitic flatworms. With the Gallic romantic touch 

 evident even in a scientific report, one writer puts it, "our most 

 beautiful pearl, then, is but the sarcophagus of a miserable worm." 



Pearls in Lower Cretaceous oysters tell us that parasitic flat- 

 worms appeared on the earth at least as early as mid-Mesozoic 



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