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POPULAR SCIENCE MONTHLY. 



inches in length, resembling somewhat the farm-fence lizards of 

 to-day. In the Permian era, closing the Pelseozoic realm, other 

 cotylosaurs appeared in nnmbers, first of moderate size, then gradu- 

 ally increasing in bulk. Of these were the larger Theromera, such 

 as the lizardlike Dimetrodons, some with forty-inch spines on their 

 backs, and the shell-backed, lizardlike Otocoelidoe, the ancestors of 

 the marine turtles (Testudinata), ranging from three to ten feet in 

 length. The Mesozoic realm, following, was the most extraordinary 

 period of earth for its forms of animal life. In its first section, 

 the Triassic, the saurians that appeared assumed wide orders, func- 

 tions, and greater proportions. These lizardlike saurians were termed 

 Palceoctonus, ^lEtosaurus, Dystrophacus, Thecodontosaurus, and Pa- 

 Iceohatteria. 



The Triassic, Jurassic, and Cretaceous formations, following, 

 formed the most remarkable period of types of animal life. An 

 examination shows that the marine Jurassic beds of Colorado were 

 overlaid by a former fresh-water area, or lake, in which abounded 

 iguanodons, megalosaurs, and cetiosaurs of diverse species, which 

 swarmed in vast numbers and grew to gigantic proportions. The for- 

 ests and jungles abounded in saurians which walked upon four legs 

 and were so armed as to preserve peace while they fed on vegetation. 

 The Cretaceous agathaumas resembled somewhat in form the rhi- 

 noceros, and the Jurassic stegosaur partook of the bulk of the elephant. 



Under side of Skull of Ttlosaurus proriger (Cope). 



Agathaumas had a powerful skull, with two long horns over the eyes 

 pointing upward and one over the nose pointing forward. The 

 stegosaurs had a wonderful dermal armor of plates and spines arising 

 along the spinal column. Such were the more specialized types of the 

 forest. The plains and fields swarmed wdtli saurians which ran or 

 leaped on two hind legs and tail, tripod fashion, and whose fore limbs 

 were used for seizing prey or supports. Those of the kangaroo type 

 are represented by the Laramie Cretaceous LceJaps incrassatus 



