Contents Updated: Thursday, August 05, 1999
Once warm-bloodedness arrived, it stayed. The cold-bloods were never able to gain control again. They evolved too slowly to fill the empty niches created by mass extinctions of the warm-bloods. Even the paleontological establishment accepts that the wolf-headed cynodonts were surely warm-blooded. So if dinosaurs were cold-blooded they could not have replaced them.
You might argue that even in The Age of the Mammals a lot of cold-blooded animals like tortoises and snakes have thrived though not as the dominant life form. Couldn't the dinosaurs, though cold-blooded, have done the same, biding their time to eventually wrest control from the pre-mammals. It sounds feasible perhaps, but, though cold-blooded animals remain numerous in the world of the mammals, we saw above that they have occupied specialized niches in which they have avoided direct confrontation with the warm-bloods. Their survival has depended on that.
Tortoises evolved from turtles by adapting for a life on land about 50 million years ago, after the demise of the dinosaurs. On dry land the tortoise was in apparent competition with mammals, also free to occupy empty niches left by the dinosaurs. It succeeded to such an extent that one species called colossochelys grew as big as a small car. But the tortoise was not in direct competition with the mammals! It did not try to out-do the mammals at their own game!
Instead it made the best of the qualities that it had—an armored carapace and the infinite patience conferred upon it by its slow, cold-blooded metabolism. Harried by a predatory mammal the tortoise, like a feudal baron, withdrew into its keep, pulled up the drawbridge and settled down to withstand the siege. And the tortoise could wait a lot longer than any mammal.
The colossochelys survived for millions of years until recent times, able to withstand anything mammals could come up with—until they invented man. The intelligent mammal realized that not only was the giant tortoise helpless on its back but it also carried with it a conveniently large stewpot. Groups of men were soon levering the tortoises on to their backs and building bonfires underneath them. The result is that no colossochelys remains in the world today.
There are about as many species of snake living on the land as there are mammals. Snakes are predators but ones that, like the herbivorous tortoises, make the most of their own special features including the infinite patience of the cold-bloods. The snake is able to poise unseen, because of its unusually extended shape, and totally motionless, because of its cold-blooded metabolism, until some careless victim stumbles upon it, whereupon it is swiftly poisoned or more slowly constricted. Snakes make the most of what they have and do not actively compete with warm-blooded mammals.