172 NEW YORK STATE MUSEUM 



Life of the Triassic period 

 In the Triassic was the reign of the amphibians, some of which 

 were very large. The most highly developed was the labyrin- 

 thodon, which had the form of a frog and was as large as an ox. 

 Reptiles were very large and numerous but their remains are 

 more abundant in Europe than America. The mammalian fauna 

 was insignificant; fishes were numerous; mollusks were abun- 

 dant, but were not a prevailing type. 



JURASSIC SYSTEM 



The connection between the Triassic and Jurassic is very close 

 and the passage is very gradual. The Jurassic takes its name 

 from the Jura mountains of France and Switzerland, which are 

 chiefly composed of the rocks of this age. In eastern North 

 America the Jurassic is moderately developed, and it is con- 

 sidered that a part of the Triassic sandstone, already described, 

 may have been deposited during this age. 



West of the Mississippi the Jurassic is well developed. 



Life of the Jurassic period 



The Jurassic was especially characterized by the prominence 

 of reptilian life which appeared in a great variety of forms 

 and occupied every place in nature. Reptiles were large and 

 numerous, in the ocean and on land. Even in the air immense 

 lizards with wings like those of a bat were abundant. In this 

 age the first of the birds appears. This was the archaeopteryx, 

 found in the slates of Solenhofen, Germany, a bird which was 

 rudimentary in its development. The wings were short and also 

 the wing feathers which were radiated. The tail was vertebrated 

 and the vertebrae bore feathers. It had no teeth. The sharks 

 and ganoid fishes were large and abundant. The mammals were 

 numerous, but subordinate in rank, not being larger than rats 

 and opossums. 



In this system also was the culmination of the ammonite fam- 

 ily, a group of coiled cephalopods named from their resemblance 

 to the horns on the statues of Jupiter Ammon. As the cephalo- 



