Could Climate Change Drive Crocodiles Back to Europe?

Scientists say Europe has no natural crocodiles because the cooling planet caused a reptilian retreat to warmer climes. Could crocs spread anew as our world warms?

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The extinct crocodile Sarcosuchus, which could reach 12 meters in length an dlived 110 million years ago.
The extinct crocodile Sarcosuchus, which could reach 12 meters in length an dlived 110 million years ago.Credit: Nicholls, 2015

Tragically, Europe has no natural crocodiles, outside of zoos at least – not because of primordial hunters but because the cooling planet caused a reptilian retreat to warmer climes, say scientists, following a massive review of data of climatic history and the entire known fossil record of crocodilians.

The mass extinction event 66 million years ago that wiped out most dinosaurs, except ones that evolved into birds, and many other life forms on earth had actually smiled upon the croc. It is true that many did disappear – but others thrived, spreading like fanged weeds into new territories.

But though the rise of the crocodilian lasted for tens of millions of years, it was not to last forever.

Fluctuation in ocean levels and global climate cooling over millions of years caused a material decline in the number of crocodilian species, to a mere 23 today (of which several are endangered). But there used to be a lot more, some impressively large, and they flourished in the northern hemisphere too, says a new study published in Nature Communications by a collaboration of researchers from Imperial College London, the University of Oxford, the Smithsonian Institution and the University of Birmingham.

Being reptiles, crocodiles are cold-blooded, relying on the sun for warmth. The colder the weather, the more sluggish their metabolisms. As the northern hemisphere cooled, the crocs went south.

It isn't that they lived in clover there either – crocs also need water to sustain their lifestyle. At the more southern latitudes the hapless crocodilians encountered desertification.

For instance, about 10 million years ago, the Sahara desert for instance began to form from what had been gorgeous wetlands and savanna, that had been ideal for our reptiles. And in South America, says the paper, the rise of the Andes Mountains led to the loss of a vast pre-Amazonian wetland habitat that crocodilians had lived in and loved five million years ago.

Thus crocodile species became geographically constrained from practically the whole world to narrower areas in North and South America, and Africa of course.

"Millions of years ago these creatures and their now extinct relatives thrived in a range of environments that ranged from the tropics, to 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," stated Dr Philip Mannion, joint lead author from the Department of Earth Science and Engineering at Imperial College London.

For all their fearsome reputation, ergo, crocodiles are vulnerable, Mannon added. "Looking back in time we've been able to determine what environmental factors had the greatest impact on them. This may help us to determine how they will cope with future changes."

By which he means the opposite procedure – global warming, which scientists agree almost to a man, is afflicting our planet.

Theoretically, as the oceans and other water bodies warm with the rest of the globe, crocodilians could reverse their contraction and start to spread. But that depends on other elements too, such as people not killing them when spotting them swimming in their local waters, whether out of fear, or to eat them – many consider crocodile meat to be a delicacy.

The group of crocodilians today includes crocodiles, alligators, caymans and gharials (also known as gavials). Some consider them to be an extremely evolved form of live, given that they go back hundreds of millions of years: a crocodilomorph, Carnufex carolinensis, that walked on its hind legs was believed to be the top predator in North America around a quarter-billion years ago, before dinosaurs even evolved.

Others note their small brains, which don't even have the section that feels emotion.

Israel also had crocodiles once upon a time, naturally occurring ones, until the early 20th century. The only ones still surviving in the country are in zoos and at the Hamat Gader crocodile farm.