What a croc! 13 millions years ago, crocodiles dominated a patch of the Amazon
It takes just one species of alligator to add an aura of menace to Florida's canals and golf ponds. Now imagine a swamp hosting not one kind of croc, or even two, but seven.
This conclave of crocs is no fictional horror story. New fossil discoveries show that an unprecedented seven species of crocodilians – a family that includes the American alligator, the Central and South American caimans and others -- inhabited the same patch of territory 13 million years ago in what is now the western Amazon.
The seven range from a powerful predator as long as a stretch limousine to a newfound croc with bulbous teeth for crushing clams. Together they provide new insights into the crazy-quilt biodiversity that characterizes the modern-day Amazon.
"It was a real crocodilian community," says study co-author Rodolfo Salas-Gismondi of the Museum of Natural History in Lima, Peru. "To find seven species … is just amazing."
In today's Amazon, any particular patch of jungle is shared by no more than three species of crocodilians. But just outside the Peruvian city of Iquitos, researchers found two rock outcroppings containing fossil evidence for seven kinds of croc co-existing in a kind of natural Gatorland. Salas-Gismondi credits the variety of toothy reptiles in part to the richness of their environment, a vast wetland that offered a limitless buffet of things to eat.
The resulting cast of characters at the Iquitos site included the previously discovered Purussaurus neivensis, an apex predator that preyed on mammals and turtles. There was also Mourasuchus atopus, a giant croc that seems to have filtered water through its mouth to consume fish.
And then there were the three crusher crocs, all of them new to science, the scientists report in this week's Proceedings of the Royal Society B: Biological Sciences. The star of the show is the Gnatusuchus, or "small-nosed crocodile." The first skull emerged from the mud in 2006, only to be nearly crushed when the pilot of the scientists' motorboat jumped to shore to tie up the vessel.
"The thing was sitting there with the top of the skull and the eyeballs looking at us," recalls study co-author John Flynn of the American Museum of Natural History in New York City. "It was just an incredible feeling … knowing immediately it was something so different."
With its short, shovel-shaped snout, Gnatusuchus strikes a bizarre figure. Researchers believe it rooted through muddy lake bottoms in search of clam-like mollusks and crushed its prey in its chunky back teeth. Confirming this theory, numerous mollusk shells bearing the scars of a crushing injury have also been found at the same fossil site.
"I didn't really think of crocs as being clam-eaters before," says vertebrate paleontologist David Schwimmer of Georgia's Columbus State University, who was not involved with the research. "It's not exactly ferocious, hunting down the giant killer clam. Just think of the image."
The scientists also discovered two more crusher crocs, one christened Kuttanacaiman, or "crushing-machine caiman," and the other named after an American paleontologist. Croc No. 6 is a pointy-toothed caiman that is either an early example of a living caiman species or a recent ancestor of that species, and No. 7 is a new species with a snout so long and narrow it looks like a fencer's foil.
The mixture suggests that Amazonian diversity comes from recently evolved species added to older creatures, Flynn says. Gnatusuchus in particular should help scientists understand the history of the caiman family, according to Douglas Riff of Brazil's Federal University of Uberlândia. "These are all fossils that any paleontologist would love to study," Riff adds via email.
The collection of crocs adds to the evidence that crocs ruled South America "until very recently," University of Iowa paleontologist Christopher Brochu says via email. These animals "were common, diverse and very large. … Anything approaching the water would have risked an unpleasant death."