THE CRETACEOUS PERIOD 



265 



fication, but rather it is a simple arrangement for convenience of 

 elementary discussion. Unless otherwise stated the types men- 

 tioned ranged through the whole Mesozoic. 



Enaliosaurs. — There are many known types of these swim- 

 ming Reptiles, but only a few of the most typical and characteristic 

 forms are chosen for description. 



The Ichthyosaurs were Fish-like forms which ranged in length 

 up to 25 or 30 feet. They had stout body, very short neck, and 

 very large head (see Fig. 164). The head, sometimes 4 or 5 feet 

 long, had an elongate snout in which as many as 200 large sharp 

 teeth were set in grooves (not in sockets). Enormous eyes, some- 

 times over a foot in diameter, were protected by bony plates. A 

 powerful tail with 

 two lobes set ver- 

 tically had the 

 vertebral column 

 extending through 

 the lower lobe. 

 The four limbs 

 were perfectly con- 

 verted into swim- 

 ming paddles, thus 

 strongly suggesting 

 that these, as well as other Enaliosaurs, represent former land 

 Reptiles which adapted themselves to a water environment much 

 like certain Mammals of today, such as Whales and Dolphins. 

 Fishes and Cephalopods were largely their prey, as proved by the 

 fossil contents of their stomachs, no less than 200 Belemnite 

 remains having been found in one specimen alone. Many remark- 

 ably preserved specimens of Ichthyosaurs have been discovered 

 (Fig. 165), some with even the embryos plainly visible within the 

 bodies. Ichthyosaurs ranged through the whole Mesozoic. 



Plesiosaurs were less powerful forms than Ichthyosaurs, 

 though they were usually longer, some having attained a maximum 

 length of 40 to 50 feet (Fig. 166). A stout body, long slender 

 neck, small head, short tail, and four powerful paddles were char- 

 acteristic features. Sharp teeth were set in sockets (not grooves) 

 in the jaws. With their slender, serpent-like necks, often 10 to 

 20 feet long, "the Plesiosaurs could lie motionless far below the 

 surface, occasionally raising their heads above the water to breathe, 



Fig. 165 



A well-preserved Ichthyosaur found in Germany. 

 (After Fraas.) 



