Giant Crocodylians, Not Mammals, Ruled Miocene South America's Food Chain, Study Finds

More than 10 million years ago, a vast lake spread across much of South America, home to giant turtles and crocodylians in its waters and anacondas, saber-toothed mammals, flightless "terror birds" and sebecids -- terrestrial relatives of crocodylians -- hunting along its shores. New research suggests that among all these predators, crocodylians played the dominant role in this Miocene-era ecosystem.

"There was so much prey available that mammalian predators couldn't have eaten it all," said Oscar Wilson, a postdoctoral researcher at the University of Helsinki. "Our new study shows that crocodylians in particular were the region's most important predators, especially when it came to hunting large prey." The lakeshore also supported an extensive range of herbivores, including giant ground sloths, glyptodonts -- armadillo relatives -- and ungulates such as astrapotheres and toxodontids, some weighing well over a metric ton.

The largest known predator in the ecosystem was Purussaurus neivensis, a relative of modern caimans that grew to about seven meters long and weighed roughly 1,800 kilograms. As an apex predator, the study suggests it may even have helped shape the size of local herbivore populations.

To reconstruct these ancient interactions, researchers examined fossils held in museum collections dating from 10.5 million to 16 million years old, looking for bite and tooth marks -- the only direct evidence linking specific predators to their prey. "The frequency of marks likely made by Purussaurus suggests that it was an important predator in these tropical ecosystems," Wilson said. The study was published in the Journal of Vertebrate Paleontology.