ABSTRACT
The first land animals of which we have fossils are flightless insects, presumably descended from something like the modern crustaceans. Their living descendants are the birds and the crocodiles. A great number of them walked on their hind legs and used their fore paws for grasping. The existing lizards and snakes are only distantly related to them, being descended from a group which was not very important during the great age of reptiles. Fortunately the ancestral mammals, descended from a group of reptiles who had almost disappeared before the archosaurs, were there to take their place. The most original mammals are whales, elephants and men. The largest whales are all filter-feeders. The largest reptiles ate plants or fairly large animals. But the great whales have no teeth. They live on shoals of shrimp-like crustaceans which they strain out of the sea with their sieves of 'whalebone' which have replaced their teeth.
