A 23-Foot Crocodylian May Have Ruled South America's Ancient Food Chain

More than 10 million years ago, during the Miocene epoch, a vast lake covered a large part of South America, supporting giant turtles, crocodylians, and an unusual cast of predators, including anacondas, saber-toothed mammals, flightless "terror birds" and sebecids, land-dwelling relatives of crocodylians. New research indicates that despite this competition, crocodylians, not the mammalian predators, were the ecosystem's most significant hunters of large prey. "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 lake's shores supported abundant herbivores, including giant ground sloths, glyptodonts, heavily armoured relatives of armadillos, and ungulates, or hoofed mammals, such as astrapotheres and toxodontids, some weighing well over a metric ton. The largest known predator was Purussaurus neivensis, a giant crocodylian related to modern caimans that grew to roughly seven metres, about 23 feet, and weighed around 1,800 kilograms.

To determine which predators were actually attacking prey, researchers examined bite and tooth marks preserved on fossilized herbivore remains in museum collections, ranging from 10.5 million to 16 million years old, the only direct evidence of predator-prey interactions available, since size and anatomy alone cannot confirm what an extinct animal actually hunted. "The frequency of marks likely made by Purussaurus suggests that it was an important predator in these tropical ecosystems," Wilson said. The study suggests Purussaurus may have been influential enough to affect the size of herbivore populations across the ecosystem.

The study, which analyzed fossils from the period, was published in the Journal of Vertebrate Paleontology.