528 THE COMANCHEAN PERIOD 



Climate 



In the aggregate, the known fossils of the Lower Cretaceous of 

 America are not such as to indicate great diversity of climate. 

 Even in Greenland, the climate seems to have been as warm as that 

 of warm temperate regions to-day. 



The fresh-water fossils of those deposits of central Europe 

 which represent the transition from the Jurassic to the Lower Cre- 

 taceous, indicate a climate far from tropical. It would seem to 

 have been comparable to that of the temperate portions of America 

 to-day. The fossils of lower latitudes denote a warmer climate. 

 On the whole, European fossils seem to afford better evidence of the 

 existence of climatic zones than those of America. 



LIFE 



Land vegetation. Fossil plants constitute the chief record of 

 the life of the early stages of the Comanchean in America. The 

 earliest flora was akin to that of the Jurassic, the cycadeans (Fig. 

 447), conifers, ferns, and horsetails being the dominant forms. In 

 most of Europe, this group held possession of the land throughout 

 the period, though angiosperms appeared in Portugal before its 

 close. Descendants of Jurassic types of plants also continued 

 throughout the period in northwestern America. 



Introduction of angiosperms. This period was marked by one 

 of the most radical evolutions in the history of the plant kingdom. 

 Angiosperms (p. 685), including both monocotyledons and dicoty- 

 ledons, appeared early in the period, and developed so rapidly that 

 by the beginning of the next they had overrun the continent. Their 

 precise time and place of origin is not known, but present data 

 point to the borders of the north Atlantic as the place of origin, 

 and the late Jurassic or earliest Comanchean as the time. 



About 400 species of Comanchean angiosperms are known from 

 the Atlantic coast. They were in a minority in the lowest Potomac, 

 but increase to an overwhelming majority in the upper beds. The 

 earliest forms are not really primitive, and throw little light on the 

 origin of the group. The majority resemble modern genera, and a 

 few (as Sassafras, Ficus, Myrica, and Aralia} are referred to living 

 genera. Before the end of the period, figs, magnolias, tulip trees, 

 laurels, and other forms referred to modern genera, but not to mod- 

 ern species, had appeared. By this time the cycadeans had dropped 



