MESOZOIC TIME — TRIASSIC AND JURASSIC. 



761 



OOoo 



o 



OOoo o 



O a- -V 



Fig. 1206, Baptanodon discus, left Mnd paddle (x |); /, femur ; t and m, 

 bones answering to tibia and fibula ; I, first digit ; V, fifth digit. 

 Marsh. 



1315 a, page 784); (2) in their locomotive organs or paddles (Fig. 1206) which 

 are fin-like in having no defined limb-bones beyond the upper, the rest of the 

 limb being represented 

 by several series of 

 bones, and the number 

 of series exceeding the 

 normal number of fin- 

 gers, five ; and (3) in 

 the absence of a breast 

 bone, and the presence 

 of dorsal fins. The 

 specimens from Wyo- 

 ming of Baptanodon 

 discus of Marsh indi- 

 cate a species eight or 



nine feet in length, with a toothless head and the orbit of great size (as in 

 Ichthyosaurs, page 784), with a sclerotic ring of 8 plates, which is conical as 

 in some birds. 



Dinosaurs. — Localities in Colorado and Wyoming are the most important 

 source of what is known about Jurassic Dinosaurs. They were the most 

 gigantic of terrestrial animals, in some cases reaching a length of 70 or 80 feet, 

 while at the same time they had a height of body and massiveness of limb that, 

 without evidence from the bones, would have been thought too great for 

 muscle to move. Besides this, some of the huge beasts had the most 

 diminutive of brains; but, as a compensation, a nervous mass in the 

 sacrum 20 to 30 times as large as the brain for use in connection with the 

 hinder limbs and tail. There were both Carnivorous and Herbivorous kinds, 

 the latter the inferior. 



The American Herbivorous species are of three groups : (a) The 

 Sauropods or Saurian-footed ; kinds having the fore and hind limbs nearly 

 equal, crocodile-like, with all the feet five-toed (that is, with five usable 

 toes); the limb bones solid, but the vertebrae, especially the anterior, 

 cavernous, and thereby light, (b) The Stegosaurians, having very short 

 fore limbs ; the fore feet five-toed and hinder three-toed ; the limb bones and 

 vertebrae solid ; and the body covered with bony pieces or plates ; the 

 vertebrae all biconcave, (c) The Ornitliopoda or bird-footed, having very 

 short fore limbs with the long hind limbs three-toed, bird-like, rarely four- 

 toed ; the bones of the hind limbs hollow, but the vertebrae solid. (Marsh.) 



The Carnivorous species have in all cases the fore limbs short compared 

 with the hind limbs, and the latter usually three-toed, bird-like. The limb 

 bones are hollow, and the vertebrae are more or less cavernous, in order, as 

 in birds, to have less to lift, especially in the anterior part of the body. 



The following are some examples of Jurassic species under the several 

 subdivisions. The specimens are all from the Atlantosaurus beds of Colorado 

 and Wyoming. 



