82 THE LESSON OF EVOLUTION 



gradually passed into forms like modern fishes, with a 

 well ossified skeleton, bony scales, and homocercal 

 tails. In the Jurassic period sharks appeared with 

 sharp, pointed teeth in their jaws ; but they were not 

 common until the Cretaceous. The first skates are 

 also Jurassic. 



The Triassic and Jurassic forests consisted chiefly 

 of short-stemmed cycads and pines, with an under- 

 growth of ferns. There is little or no advance on 

 the flora of the Deutozoic era, the difference being 

 chiefly due to the absence of the large Equisetaceee 

 and Lycopodiacese of the Carboniferous, combined with 

 a great increase of Gymnosperms. In the Cretaceous 

 period, however, we find a great improvement ; for here 

 we have the dawn of the modern flora. In addition 

 to palm trees and other Monocotyledons, Dicotyledons 

 are abundant in the lower Cretaceous of North 

 America and of Portugal ; and in the upper Cretaceous 

 this flora spread through Europe into Greenland, even 

 as far as 81 45' K 



Part of the early Mesozoic flora of Europe is 

 thought by some naturalists to have originated in the 

 southern hemisphere, and to have migrated northwards 

 from Australia through India. But there appears to 

 be no good evidence of this except with the genus 

 Grlossopteris, which is Permo-carboniferous in Australia, 

 and associated with Cordaites, Cyclostigma, Lepidoden- 

 dron, Calamites and Sphenopteris. Among the vege- 

 tation insects were common. In addition to the 

 Orthoptera and Neuroptera, already noticed, we now 

 have beetles, cicadas, flies, and ants. 



The Mesozoic has been well called the age of 

 reptiles, so numerous and varied were they. A very 



