358 AN INTRODUCTION TO THE STUDY OF FOSSILS 



possessed a gizzard. Evidence is also accumulating to indicate 

 that the stomachs of some dinosaurs, both carnivorous and 

 herbivorous, had a gizzard-like compartment. 



Order 4, I chthyo pterygia {Ichthyosaurs) 



Extinct aquatic reptiles, with large head, no neck, and a 

 long tail expanded in a vertical plane ; they are thus fish-like 

 (whence the name from Greek ichthys, a fish, + pterygia, fins). 

 The two pairs of limbs are true paddles. They doubtless 

 swam largely beneath the surface of the water, but were com- 

 pelled to come to the surface for breathing. Within one indi- 

 vidual were found the internal skeletons of two hundred belem- 

 nites ; such records as well as the fish scales and bones in the 

 many coprolites left by them indicate that they lived largely 

 upon fish and cephalopods. 



These ichthyosaurs, Triassic to Cretaceous in age, parallel 

 the whales amongst the mammals but were smaller, with a 



Fig. 152. — The ichthyopterygian reptile, Ichthyosaurus quadriscissus, from the 

 Jurassic of Germany. This remarkably preserved form shows not only the outline 

 of the dorsal and caudal fins, but also the integument surrounding the limbs. 

 fe., femur; hu., humerus: ob., orbit of eye ; ra., radius; ul., ulna. (After Fraas, 

 from Woodward's " Vertebrate Paleontology.") 



maximum length of twenty to thirty feet against sixty to seventy 

 for the whales. Some at least bred their young alive, producing 

 eight to ten at a birth. They indicate, as do the whales, a 

 derivation from land forms; the bones of the forearm (radius 



