More than 10 million years ago, a vast lake and wetland system spread across much of South America, hosting an ancient ecosystem where giant crocodylians dominated large prey hunting, according to research published in the Journal of Vertebrate Paleontology. During the Middle Miocene epoch, between 10.5 million and 16 million years ago, the region supported an extraordinary collection of predators and prey across its waters and shores.
Giant Crocodylians Ruled Miocene South America
While anacondas, saber-toothed mammals, flightless terror birds, and terrestrial sebecids hunted along the landscape, a study led by researchers at the University of Helsinki demonstrates that crocodylians served as the primary apex predators in these tropical wetland ecosystems.
There was so much prey available that mammalian predators couldn’t have eaten it all,
says Oscar Wilson, 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.
An Ecosystem Packed With Megafauna
The tropical lake shores supported a remarkable variety of massive herbivores. These included giant ground sloths, heavily built glyptodonts as relatives of armadillos, and several groups of native ungulates. Among the hoofed mammals were toxodontids and elephantine astrapotheres, also known as lightning beasts. Many of these ancient herbivores reached enormous sizes, routinely weighing well over a metric ton, or a tonne.
To support such massive herbivores, the region also fostered predators of immense scale. The largest known predator in the ecosystem was Purussaurus neivensis, a massive relative of modern caimans. Growing to about seven meters in length and weighing roughly 1,800 kilograms, this apex predator occupied the top tier of the food web.
Because mammalian carnivores alone lacked the capacity to consume the immense biomass of large prey, giant crocodylians filled the role of primary megafaunal hunters. Researchers note that Purussaurus neivensis may have been influential enough to affect the size of herbivore populations, exerting top-down control over the prehistoric ecosystem.
Fossil Evidence and Bite Trace Analysis
To reconstruct these ancient interactions, researchers examined fossil collections preserved in museum repositories. Because direct behavioral observations are impossible, bite and tooth marks left on herbivore remains provide the only direct physical evidence of interactions between species.
The frequency of distinct bite and tooth marks matched to Purussaurus neivensis indicates that these aquatic giants actively hunted the continent’s largest land animals. In one specific instance from the Colombian fossil site of La Venta, researchers analyzed a broken leg bone cataloged as MT-0200 belonging to a large terror bird. Four shallow pits on the bone, featuring grooves and indentations that preserved the shape of tooth tips and cutting edges, showed no signs of healing.
A previous study published in Biology Letters concluded that these tooth marks fit a large caimanine, most plausibly a juvenile or subadult Purussaurus neivensis measuring roughly 4.6 to 4.8 meters long, though the fossil leaves open whether the crocodylian made an active kill or scavenged a body near the water.
