The Amazon Rainforest was Dominated by Crocodiles 13 Million Years Ago

It turns out that 13 million years ago, parts of Peru were dominated by crocodiles. As many as seven different species of crocodiles hunted in the swampy waters, which reveals a bit more about the past climate and ecosystem of the region.

Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, filled with lakes, embayments, swamps and rivers that all drained northward toward the Caribbean. This was different from today's pattern of an eastward flow toward the Atlantic Ocean.

The researchers spent more than a decade examining remains in Amazon bone beds. This revealed that 13 million years ago, the region supported the largest number of crocodile species co-existing in any one place at any time in Earth's history.

"The modern Amazon River basin contains the world' richest biota, but the origins of this extraordinary diversity are really poorly understood," said John Flynn, one of the researchers, in a news release. "Because it's a vast rainforest today, our exposure to rocks-and therefore, also to the fossils those rocks may preserve-is extremely limited. So any time you get a special window like these fossilized 'mega-wetland' deposits, with so many new and peculiar species, it can provide novel insights into ancient ecosystems. And what we've found isn't necessarily what you would expect."

Three of the species that the researchers discovered are entirely new to science. One of the species is Gnatusuchus pebasensis, which is a short-faced caiman with globular teeth. This species probably used its snout to "shovel" mud bottoms, digging for clams and other mollusks. This species, in particular, reveals how diverse crocodiles were during this time period.

"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," said Rodolfo Salas-Gismondi, lead author of the new paper. "At this moment, most known caiman groups co-existed: ancient lineages bearing unusual blunt snouts and globular teeth along with those more generalized feeders representing the beginning of what was to come."

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

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