Crocodiles

While crocodiles, and their relatives alligators, caimans and gharials, are the great survivors from the dinosaur age, that doesn’t make them living dinosaurs. That’s because early crocodylians appeared before dinosaurs, about 240 million years ago. During the Mesozoic era, crocodylians diversified into forms more like those we see today.

The Mesozoic era (commonly called the Age of Dinosaurs) ended 66 million years ago with a mass extinction event. Over 70 per cent of species perished, including all non-avian, or ‘non-bird’, dinosaurs (yes, birds are now classified by scientists as theropod dinosaurs). So how did crocodiles and their relatives survive this mass extinction event when many groups of animals, including non-avian dinosaurs, didn’t?

Firstly, not all crocodylians did survive (and many had gone extinct before the end of the Cretaceous period). In fact, quite a number became extinct, particularly the large-bodied ones. However, some groups clearly did survive, including the ancestors of today’s crocodylians, the group that includes crocodiles, alligators, caimans and gharials. A number of reasons have been suggested to explain their survival. These include:
• the ability to function at low body temperatures and survive on little food,
• an immune system that could endure terrible injuries,
• the ability to tolerate long periods of darkness and poor conditions,
• living in freshwater environments which were less affected by the extinction event than other habitats,
• reproducing and rearing more offspring to adulthood. Most animals either leave their many young to fend for themselves or use enormous amounts of energy to raise a small number of offspring. Crocodylians are among the few animals that do both – females lay up to 60 eggs and, along with some male crocodile species, often protect the nest and young.