Today, it is hard to associate crocodiles with the shores of an Antarctic lake. Yet the region was not always covered in ice. About 50 million years ago, Earth was much warmer, and relatives of modern crocodiles lived as far as the polar regions.
To understand how these animals survived the great crises in Earth's history, researchers studied more than 7,000 fossils and data on over 400 living or extinct species. They compared their habitats with the climates that prevailed at different times over nearly 245 million years.
American crocodile in the marshes of La Manzanilla, in the state of Jalisco, Mexico.
Tomas Castelazo · CC0 · Wikimedia
The result is fairly straightforward: despite their diversity, members of this large family mainly sought warm regions. When the planet warmed, they could live much farther from the tropics, as far as Antarctica. When it cooled, their territory moved closer to the equator.
This habit may have saved their lives 66 million years ago, when an asteroid impact caused the extinction of the non-avian dinosaurs. Dust thrown into the atmosphere reduced sunlight and cooled the planet abruptly. But not all regions became equally hostile.
The researchers simulated several climate scenarios after the impact. In most of them, some areas near the equator remained warm enough to support ancestors of modern crocodiles. These refuges may have allowed populations to survive before spreading again when conditions improved.
Climate does not explain everything. Their ability to live in water, feed on a variety of foods and endure long periods without eating probably also played a role. Some of their ancient relatives were very different from today's crocodiles: they included land-based hunters and even herbivorous species.
Their presence in polar regions, particularly after the extinction of the dinosaurs, mainly reflects their ability to follow areas where the temperature suited them.
This dependence on warm climates could nevertheless become a problem today. If temperatures change rapidly and roads, cities or farmland block their movements, crocodiles will not always be able to reach new favorable habitats.