PAST DISTRIBUTION OF ANIMALS 



543 



which is known as the age of fishes. The more modern fishes, the 

 teleosts, were not known until the Jurassic and are represented now by the 

 greatest number and diversity of species they have ever possessed. A 

 footprint from the Devonian is the earUest trace of an amphibian. There 

 were giant armored amphibians, the Stegocephala, in the Pennsylvanian 

 and Permian periods. These reached a maximum length of 15 to 20 

 feet in the Triassic, when they became extinct. The reptiles appeared 

 about the time of the amphibians but did not become dominant until 

 the Mesozoic, which was the age of reptiles; they reached their highest 

 development during the Jurassic. The aquatic and marine types 

 attained a length of 40 feet; a flying pterodactyl had a wing spread of 25 

 feet; and the gigantic dinosaurs reached 100 feet in length. These 

 giants suddenly became extinct in the Cretaceous. 



Fig. 375. — Archidiskodon maiheni Barbour, one of the largest skeletons of a mammoth 

 on record — 14 feet at the shoulder — in comparison with the skeleton of a recent Indian 

 elephant and with the two men standing under it. {Photographed from a specimen in the 

 University of Nebraska State Museum.) 



Fossil remains of the earliest bird, Archaeopteryx (Fig. 297), have been 

 found in the Jurassic slates of Bavaria, and a number of other birds 

 are known from the Cretaceous. The earliest mammalian remains are 

 from the upper Triassic, and many types are known from the Creta- 

 ceous. Mammals have been dominant since the beginning of the 

 Cenozoic era. Human origins have already been discussed. Steps in 

 the development of other mammalian types will be referred to in the next 

 chapter, on evolution. 



