Giant Crocodylians Ruled Miocene South America’s Food Chain
Ten million years ago, the top predator prowling South America’s shorelines wasn’t a mammal at all. According to new fossil evidence, it was a seven-meter crocodylian weighing nearly two tons, and it may have been powerful enough to shape the size of entire herbivore populations.
A Continent Ruled by Giants
More than 10 million years ago, during the Miocene epoch, a vast lake system covered much of South America, part of what researchers call the Pebas megawetland, a freshwater lake network with interconnected waterways spreading across the continent’s northwest. Its waters supported giant turtles and crocodylians, while an extraordinary range of predators hunted along its shores, including anacondas, saber-toothed mammals, flightless terror birds, and sebecids, land-dwelling relatives of crocodylians.
Despite that intense competition, a new study led by researchers at the University of Helsinki indicates that crocodylians, not mammals, were the most significant predators in this habitat. The findings were published in the Journal of Vertebrate Paleontology.
“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.”
A Buffet of Giant Herbivores
The lake shores supported a remarkable variety of plant-eating animals. Giant ground sloths lived alongside glyptodonts, heavily built relatives of armadillos, and several groups of hoofed mammals known as ungulates, though many extinct South American forms looked nothing like familiar horses or deer. Among them were astrapotheres, whose name translates roughly to “lightning beasts,” and toxodontids, some of which reached enormous sizes and weighed well over a metric ton.
That abundance of large prey helped support predators equally impressive in scale, chief among them Purussaurus neivensis, the largest known predator in this ecosystem.
A Truck-Sized Hunter
Purussaurus neivensis, a massive crocodylian related to modern caimans, grew to about seven meters in length and weighed roughly 1,800 kilograms, comparable in mass to a small truck. It’s worth being precise about which Purussaurus this is: P. neivensis is not the same as the later, even larger Purussaurus brasiliensis that lived in the Amazon region and is sometimes confused with it in casual comparisons.
Its immense size placed it near the top of the food chain, where the new study suggests it may have done more than simply hunt individual animals. Researchers propose that Purussaurus could have been influential enough as a predator to affect the size of herbivore populations across the wider ecosystem, shaping the community around it rather than just living within it.
Reading Bite Marks Left on Bone
To determine which animals were actually doing the hunting, rather than simply guessing based on anatomy or presumed strength, researchers examined fossils held in museum collections, focusing on bite and tooth marks preserved on the fossilized remains of herbivores. These marks are especially valuable because they provide the only direct physical evidence of interactions between predators and prey, rather than inferences drawn purely from body size or jaw shape. The fossils analyzed ranged from 10.5 million to 16 million years old, recovered from the La Venta region of Colombia’s Huila department.
The research team, led by Wilson and including colleagues from Colombia, France, Argentina, Canada, and the United States, examined four fossilized bones belonging to three species of large hoofed mammals from the region: Pericotoxodon platignathus, a rhinoceros-sized relative of ancient South American ungulates, and two elephant-like herbivores from the genus Xenastrapotherium. “The frequency of marks likely made by Purussaurus suggests that it was an important predator in these tropical ecosystems,” Wilson said.
An Ambush Hunter, Not a Chaser
The pattern of damage on the bones offers clues about hunting style as well as frequency. Three of the four examined specimens carried marks on the head or jaws, a pattern that echoes the hunting behavior of modern saltwater and Nile crocodiles, which typically ambush prey at the water’s edge, seize the head or neck, and hold or roll rather than chase prey down on land.
Some of the bite-force estimates associated with Purussaurus in the wider scientific literature run extremely high, with certain reconstructions on thin bone approaching or exceeding 40,000 newtons per tooth, though researchers caution that at least one such figure likely represents an overestimate rather than a typical bite. A separate, frequently cited 2015 biomechanical study produced very high whole-jaw force estimates for the genus Purussaurus more broadly, and some coverage of this new research has mixed those older, larger-species figures in with P. neivensis specifically. This study’s authors are careful to keep the two distinct.
More Than Just a Predator
Beyond directly killing large herbivores, researchers say Purussaurus likely played a broader ecological role by providing leftovers for scavengers further down the food chain. One examined jawbone, belonging to Xenastrapotherium kraglievichi, showed marks consistent with both predation by Purussaurus neivensis and possible subsequent scavenging by another species, Langstonia huilensis, illustrating how a single kill could ripple outward to support other animals in the ecosystem.
That combination, dominant apex predator and food source for the wider community, points to just how central giant crocodylians were to the functioning of this now-vanished tropical world, a role that modern mammal predators, however fearsome, simply couldn’t match at this particular moment in South America’s deep past.
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