430 



THE GENERAL PRINCIPLES OF ZOOLOGY 



meters high. Ichthyornis may be mentioned as an example of 

 the latter order ; it likewise lived in North America, was some- 

 thing like the terns, but had teeth in both jaws. Thus the 



FIG. 410. Hesperorms regalis, a fossil diving and swimming bird of North America; 

 skeleton, restored. (After Marsh, from Parker and Haswell's Text-book.) 



Mesozoic birds are clearly separated from all existing orders, 

 for, as we have already noted, no living bird is provided with 

 teeth. 



Fossil remains of the Mammalia are first found in the Triassic. 

 But since these, as well as the mammalian remains in the Jurassic, 



