Crocodile evolution was rebooted by Ice Age glaciations: Study

Researchers have found that the Ice Age sea-level changes in the genomes of Caribbean and Pacific crocodiles in Panama caused the species' evolution that survived for over 200 million years. According to research conducted by the scientists at McGill University, American crocodiles (Crocodylus acutus) are found in the Caribbean and Pacific coasts of the Neotropics but they arrived in the Pacific before Panama existed. The skilled swimmer species could travel long distances and live in freshwater to marine environments, but could hardly migrate far on the overland. A study published in the journal Science found that the alteration in the genes of the crocodiles was caused nearly 3 million years ago, when the formation of the Isthmus of Panama altered global ocean circulation, connecting North and South America and establishing the Caribbean Sea.

"This resulted in widespread mixing of species on the continent and separation in the seas. On land, mammals from North America such as mammoths, saber-toothed cats, horses, and camels invaded South America, and strange mammals like giant ground sloths, armadillos, and opossums from South America invaded North America," researchers purported in the study.

Further, they explained that during this event, known as the Great American Interchange, many species evolved separately into Pacific and Caribbean waters. However, researchers speculated that the American crocodiles living on the Pacific coast should have diverged genetically enough from Caribbean populations to become unique species. But as per the new research, as scientists sequenced the crocodile's genomes, it was found that the evolutionary divergence in the crocodiles was caused during the Glacial and interglacial cycles in the Ice Age. 

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[Ice Age fossil of a crocodile. Credit: Twitter/@TheFatWombat]

[Researchers sequenced the genomes of crocodiles to look for small variations in their DNA. Credit: McGill university]

Transformation during an interglacial period

Peak polar glaciations was separated by intervals of the warm periods, which caused drastic sea levels to rise over 100 meters globally compared to present-day levels, the study found. Most of Panama was underwater with the coasts separated by brackish lagoons, small rivers, and thin stretches of land. "These are the reasons why we think crocodiles were able to pass from coast to coast freely and explain why their oldest genetic signature of separation coincides with this time," Professor Larsson, Director of the Redpath Museum at McGill explained. "This time of separation is a far cry from the 3 million years we were expecting," he said, adding that it did match the last interglacial period of the Ice Age. 

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(Image Credit: Unsplash)