But the ancestral birds became adapted to flying, the ancestral Predentates to terrestrial life, and in their later development became as widely diversified in form and habits as the warm-blooded quadrupeds which succeeded them in the Age of Mammals.
[Illustration: Fig.

25 .-- Skulls of Iguanodont and Trachodont Dinosaurs.

_Iguanodon_ and _Camptosaurus_ of the Jurassic and Comanchic; _Kritosaurus_ and _Corythosaurus_ of the Middle Cretacic (Belly River); _Saurolophus_ of the late Cretacic (Edmonton); _Trachodon_ of the latest Cretacic (Lance).

The Iguanodon is European, the others North American.

All 1/25 natural size.] These Beaked Dinosaurs were, so far as we can tell, all vegetarians.
Unlike the birds, they retained their teeth and in some cases converted them into a grinding apparatus which served the same purpose as the grinders of herbivorous quadrupeds.