GIANT REPTILES OF A PAST AGE. 



473 



to the middle of tlie tail there was only one row of large scutes. 

 At the end of the tail there were, as weapons of offense, several 

 thick spines, about a foot long, so that a stroke of this tail must 

 have been telling in its effects. 



\ 



Fis. 8.— CoMPSOQNATHus (restoration by Huxley). 



Fig. 9.— Foot-pf.int of BRONTczotrM, one 

 eightli natural size (after Hitchcock). 



We have now made the acquaintance of several dinosaurs, yet 

 they are by no means all the members of this numerous order, 

 upon which already a whole literature has been published. Some 

 of them are known only by their foot-prints. The Triassic sand- 

 stone of the Connecticut Valley contains numerous impressions of 

 five-, four-, and three-toed dinosaurs, which at first were consid- 

 ered as the foot-prints of large birds. They were made when these 

 animals walked on the muddy shores of the Triassic ocean. The 

 collections of Amherst and Yale College contain each several 

 thousands of such impressions — a fact that gives some idea of the 

 abundance of reptilian life on the continent at that time. Also, 

 in Europe, we find that reptiles, and among them especially 

 dinosaurs, are the most numerous and dominating class of the 

 Mesozoic times — that is, during the Trias, Jura, and Cretaceous ; 

 so that these times are often called the age of reptiles. At the 

 end of the Cretaceous period, however, the reptiles decreased, and 

 the dinosaurs became entirely extinct — at least, we do not know of 

 any Tertiary dinosaur, and none exists at present. 



Our knowledge of these remarkable animals is a comparatively 

 recent one ; of them almost nothing was known thirty years ago, 

 but since then discoveries have followed each other in rapid suc- 

 cession, and every year contributes new data. It is especially to 

 three American scientists that we owe most of our knowledge 

 about dinosaurs; they are Prof. Josei3h Leidy and Prof. E. D. 

 Cope, in Philadelphia, and Prof. O. C. Marsh, in New Haven. 



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