210 EXTINCT MONSTERS 
Probably the large Pterodactyls of the Cretaceous period, 
soaring like albatrosses and giant petrels over the surface of the 
ocean, co-operated with the marine reptiles, such as Ichthyosaurs, 
Plesiosaurs, crocodiles, and others, as those sea-birds now do with 
the whales, porpoises, and dolphins, in reducing the excessive 
numbers of the teeming tribes of fishes, and in maintaining the 
balance of oceanic life. 
With regard to the place of Pterodactyls in the animal kingdom, 
Professor Seeley placed them as a distinct sub-class, side by side 
with birds, and between mammals and reptiles, thus— 
Mammalia. 
Ornithosauria 
Aves 
Reptilia. 
The name Ornithosauria (bird-lizards) is frequently used instead 
of the other name, because it expresses the idea of their being 
partly saurian and partly bird-like. 
They flourished from the period of the Lias to that of the 
Chalk ; and then, like so many other strange forms, seem to have 
suddenly disappeared. 
