Cold Snap and Climate Change Killed Massive Crocodilians

First Posted: Sep 24, 2015 10:06 AM EDT

A cold snap may be responsible for the retreat of crocodilians millions of years ago. Scientists have found that fluctuating sea levels and global cooling caused a significant decline in the number of crocodilian species over millions of years.

Crocodilians include present-days species of crocodiles, alligators, caimans and gavials and their extinct ancestors. These animals first appeared in the Late Cretaceous period about 85 million years ago. Since then, the fossil record has revealed quite a bit about these reptiles.

Extinct crocodilians and their relatives came in all shapes and sizes, including giant land-based creatures such as Sarcosuchus, which reached around 12 meters in length and weighed up to eight metric tons. Crocodilians also roamed the oceans; thalattosuchians were equipped with flippers and shark-like tails in order to be more agile in the sea.

Many crocodilians survived the mass extinction that wiped out almost all of the dinosaurs about 66 million years ago. Today, though, only 23 species survive. Six of these species are classified as critically endangered, and a further four are classified as either endangered or vulnerable.

In this latest study, the researchers created a dataset of the entire known fossil record of crocodilians and their extinct relatives. They analyzed data about Earth's ancient climate in order to see how the group responded to past shifts in climate.

So what did they find? At higher latitudes in areas now known as Europe and America, declining temperatures had a major impact. At lower latitudes, the decline of crocodilians was caused by areas becoming increasingly arid. For example, 10 million years ago, Africa was filled with vast, lush wetlands; however, these wetlands were replaced by the Sahara desert. In addition, fluctuations in sea levels impacted crocodilians in the ocean.

"Crocodilians are known by some as living fossils because they've been around since the time of the dinosaurs," said Philip Mannion, one of the researchers, in a news release. "Millions of years ago these creatures and their now extinct relatives thrived in a range of environments that ranged from the tropics to the northern latitudes and even deep in the ocean. However, all this changed because of changes in the climate, and crocodilians retreated to the warmer parts of the world."

The findings are published in the journal Nature Communications.

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