Ancient Shell-Crunching Crocodiles Ruled the Amazon

About 13 million years ago in what is now northeastern Peru, ancient shell-crunching crocodiles ruled the Amazon, according to new research.

Researchers studying a single Amazon bone bed found the remains of seven different crocodile species that simultaneously used to hunt in the region's swampy waters. This discovery reveals the largest number of crocodile species co-existing in one place at any time in Earth's history.

You would think that having so many fearsome predators in such tight quarters would spell trouble and lead to some stiff competition for food resources, but a team with the American Museum of Natural History shows that that is not the case.

Fossil deposits from the Amazon basin, made up of wetlands, lakes, embayments, swamps, and rivers, show that the area was abundant in invertebrates like mollusks and crustaceans. There is little evidence that vertebrates other than fish lived there.

It seems that northeastern Peru was so rich in mollusks, snails and clams that there was plenty enough to go around, creating a prehistoric crocodile paradise.

"We uncovered this special moment in time when the ancient mega-wetland ecosystem reached its peak in size and complexity, just before its demise and the start of the modern Amazon River system," Rodolfo Salas-Gismondi, lead author of the study, said in a press release.

In the study, Salas-Gismondi and his team describe the seven croc species, three of which are new to science. Possibly the "strangest" one is called Gnatusuchus pebasensis, which had globe-shaped teeth and used its snout to shovel through mud bottoms, digging for clams and other mollusks.

They also mention the crocodile Paleosuchus, which had a longer and higher snout shape that was suitable for catching a variety of prey, like fish and other active swimming vertebrates.

Gnatusuchus and other shell-crunching (durophagous) crocodiles likely dominated the Amazon millions of years ago as mollusk diversity and numbers skyrocketed. But when the mega-wetlands transformed into the modern Amazon River drainage system, mollusk populations declined and durophagous crocodile species went extinct, making way for modern-day crocodiles with a broader palate and more diverse appetite.

Today six species of caimans live in the whole Amazon basin, although only three ever co-exist in the same area and rarely share the same habitats. Never again would seven species of crocodiles in the wild live together in one place.

The findings were published in the journal Proceedings of the Royal Society B.

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