Scientists Are Mega-Stoked on Mother Lode of Croc Fossils Found in the Amazon

​You might never have guessed, since they're stone-cold predators after all, but prehistoric crocodiles appear to have been surprisingly good at being ecological roommates—much better than extant crocs.

A flood of new fossils descri​bed today in the Proceedings of the Royal Society B suggest that there was an unprecedented "hyperdiversity" of crocodiles in the Miocene Amazon, 13 million years ago. The fossils represent seven species: the largest number of co-existing crocodilians at any time in Earth's history."

"We've formally named three new species in this paper," co-author John Flynn, a paleontologist based at the American Museum of Natural History, told me over the phone.

"Two of them are a new genus, and that sort of reflects the very, very distinctive anatomies of each of those groups relative to other known caiman [crocodiles]," he continued. "There are probably additional ones that are going to turn out to be new species but we have not named them yet."

Flynn emphasized that these seven species all co-existed in the same time and place. "We're not talking about across the whole Amazon basin," he said. "We're talking about one place, living together, and that's a huge diversity."

"You never find in today's environments more than three co-occurring species, and they are rarely occurring in the same places, but they can overlap," he added.

These crocodiles hail from a very different Amazonian world, long before the region's famous river carved it into the ecological dynamo it is today. But as these evocative new findings suggest, the Miocene Amazon was as rich in evolutionary opportunity as the modern version. Its "Pebasian crocodylians," so called because they were found in Peru's Pebas Formation, were clearly thriving in the rich wetland swamps of this time.

"Pebasian crocodylians were ecologically diverse indeed," lead author Rodolfo Salas-Gismondi, chief of paleontology at the Museum of Natural History in Lima, Peru, told me over email.

"Purussaurus was a large-scale predator," he continued. "Mourasuchus was probably eating small fishes by some kind of filtering strategy, similar to that of whales. Another small caiman was a relative of the modern dwarf caiman Paleosuchus. It might have fed on insects, fishes, lizards, and small mammals."

"In terms of size they range from 1.5 meters to 10-12 meters," he added.

And that's all without mentioning the most unequivocally strange of the new species: Gnatusuchus pebasensis, a crocodile that appears to have a massive shovel for a mouth.

"We know that Gnatusuchus was specialized on feeding by head-burrowing, shoveling the muddy bottoms with its lower jaw, digging for clams, then crushing shells with the globular, tightly packed posterior teeth," said Salas-Gismondi.

No extant crocodile is even remotely like Gnatusuchus. "They're bizarre," Flynn told me. "It's a strange, strange thing. That's what was so fun in finding it. It was so unexpected."

But this study hasn't just spotlighted some highly weird new predators. It has also demonstrated the largely untapped potential of rainforests as paleontological gold mines.

"It's basically been kind of a blank slate," Flynn said of the Amazon. "You have this incredible diversity in the Amazon today of plants and animals; the world's richest biodiversity hotspot," he said. "And we just haven't known very much about that history, because there hasn't been a fossil record to tell what was there in the past."

Indeed, the Amazon been largely ignored by paleontologists in part due to pure logistics. The thick forest cover is difficult to traverse, which makes the transport of equipment and specimens a daunting task. There's also the lack of available exposures, and the assumption that anything that dies in such an opportunistic jungle environment would be picked clean before it ever had a chance to fossilize.

Even so, these obstacles don't preclude the discovery of abundant fossil beds, as Salas-Gismondi and Flynn have repeatedly discovered. "The flipside of these rainforest kinds of environments, particularly the Amazon River system, is that you have such a rich productivity," he told me. "It's often producing just so much stuff, and when it gets covered up rapidly, it can preserve things."

The river itself plays a role in excavating these rare fossil beds, which are positively teeming with fossilized remnants of the Amazon's bygone inhabitants. "[T]he rainforest covers most of the land surface, thus fossiliferous rocks are only briefly exposed during the dry season (one month a year) in the river banks," Salas-Gismondi explained.

"The Amazon River erodes continuously its river banks. Each year it 'excavates' the fossiliferous areas of the Pebas Formation and exposes new amazing fossil remains," he continued. When I asked him if novel tools like LIDAR laser scanning might help find more of these treasure troves, he said that new technologies could help, but that at the moment, "the best strategy is to go every year to rescue all of those marvelous treasures."

Because regions like the Amazon are so often written off by paleontologists as being dead ends, there is a huge gap in our knowledge of their ecological history. As today's study demonstrates, these niches were packed with exotic creatures with unique adaptations that speak volumes about the lively world in which they lived.

The revelation that these overlooked areas actually do produce abundant fossils highlights the exciting untapped potential of such places to yield even more spectacular finds in the future.

"That's one of the things that's interesting," Flynn told me. "A lot of my work has been in these areas that are relatively underexplored and not historically thought to produce fossils. I work in the high Andes Mountains, which are a volcanic terrain, but there are certain moments in time when the environments are right and the temperatures of the stuff coming off of the volcanoes are cool enough that they actually preserve fossils in their path."

"So people just didn't think to look before," he said. "But we go in and look, and we're finding an incredible record there."