476 AN INTRODUCTION TO ZOOLOGY 



some are almost complete and beautifully preserved. They varied 

 considerably in size, but were practically all large, ranging from 

 about 10 up to 50 feet in length. The body was stout and the 

 limbs transformed into two parts of large powerful paddles ; the 

 tail was fairly short, the neck long, and the mouth armed with 

 formidable teeth. In the case of Elasmosaurus, the neck reached a 



FIG. 169. Plesiosaur, Cryptocleidus, restored by Knight. 



length of 23 feet out of a total of 41 feet. The third line, the 

 Icthyosauria, also appearing in Mid Triassic strata, were also aquatic, 

 large in size, widespread, and again, have left some rem'arkably well- 

 preserved skeletons. These were more like fish or, rather, dolphins 

 in body form than the previous group, and swam vigorously by 

 means of a powerful tail. The limbs are not so large, and apparently 



FIG. 170. Ichthyosaur. Restoration by Knight. From Schnchert's 

 " Historical Geology." 



acted in the manner of fins. The neck is quite short and the head 

 pointed. They varied in size from 2 feet up to 30 feet, and possessed 

 very large eyes. Often the remains of an adult are found accom- 

 panied by those of several young, so that the offspring apparently 

 remained with the parents for some time. As noted above, the 

 Plesiosaurs and Icthyosaurs were widely spread over the globe, and 

 both groups died out in Cretaceous times ; the latter disappearing 

 in the middle strata and the former lasting on into the upper beds. 

 The fourth line of evolution is a very important one, since it led 



