MESOZOIC ERA: THE AGE OF REPTILES 521 



Life of the Mesozoic 



In the early days of the study of geology it was believed by many 

 that life ceased to exist at the close of the Paleozoic and was re-created 

 at the beginning of the Mesozoic. This belief was based upon the 

 great dissimilarity of the life of the two eras and upon the apparent 

 absence of fossils in the intermediate strata. As a more careful 

 study of these rocks was made, and new exposures were discovered, 

 fossils were found which, though rare, proved that the life was in 

 many respects transitional. The change in vegetation between the 

 two eras was not cataclysmic, as was formerly supposed, though " it 

 was rapid or almost sudden." (D. H. Scott.) The animal life suf- 

 fered even more than the plant, very few of the Paleozoic genera 

 surviving in the following era. The transition, in other words, ap- 

 parently took place with great rapidity and affected all classes of life. 

 If a change in the character of the rocks is made a basis for separation, 

 it is found that although great unconformities occur, yet in many 

 places it does not seem possible to tell where the dividing line should 

 be drawn. For example, in America (Kansas and Wyoming) be- 

 tween horizons yielding Permian fossils and those yielding Mesozoic 

 there are " at least one thousand feet of continuous, conformable, 

 uninterrupted, and homogeneous deposits of red sandstone which 

 may belong to one period or to both," and in Europe the Permian 

 in many places merges into the Mesozoic (Triassic) so insensibly that 

 it is impossible to state where one ends and the other begins. 



Comparison of the Life of the Paleozoic and the Mesozoic. — 

 The dominant plants and animals of the Paleozoic disappeared, for 

 the most part, with the Permian. The lepidodendrons, sigillarias 

 with the exception of a few stragglers, Calamites, Cordaites, spheno- 

 phylls, and a number of important genera of ferns had vanished ; 

 and their places were taken by a flora of very different character, so 

 that the forests of this era were very unlike those of the preceding in 

 general appearance. 



With the close of the Paleozoic, the abundant corals of that era had 

 disappeared and were replaced by a new type, differing (p. 524) both 

 in structure and appearance. 



No cystoids or blastoids survived. The crinoids are, with the 

 exception of two genera, of a type quite different from those of the 

 Paleozoic. The race had reached its zenith and its decline had begun, 

 though now and then a species made its appearance which by its 



