More than 10 million years ago, parts of South America looked very different from today.
During the Miocene epoch, a huge system of lakes, rivers and wetlands covered much of the continent.
Giant turtles lived in the water, enormous plant-eating mammals wandered along the shores, and some truly intimidating predators competed for food.
Among those predators were giant anacondas, saber-toothed mammals, large flightless “terror birds” and sebecids, land-dwelling relatives of modern crocodylians.
But new research suggests that another group stood above the rest: giant crocodylians.
A study published in the Journal of Vertebrate Paleontology found that crocodylians were probably the most important large predators in these ancient tropical ecosystems, particularly when it came to hunting big 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. According to the study, crocodylians appear to have played a major role in keeping populations of large herbivores in check.
The wetlands were home to an extraordinary collection of plant-eating animals. Giant ground sloths roamed the landscape alongside glyptodonts, heavily armored relatives of modern armadillos. There were also several unusual groups of hoofed mammals, including astrapotheres, sometimes called “lightning beasts,” and toxodontids. Some of these animals weighed more than a tonne.
The predators were equally impressive.
The largest was Purussaurus neivensis, an enormous relative of today’s caimans. It could grow to around 7 meters, or 23 feet, long and weigh about 1,800 kilograms, or 4,000 pounds. With its huge body and powerful jaws, Purussaurus was likely capable of attacking some of the biggest animals living around the ancient wetlands.
To understand which predators were doing the hunting, researchers studied fossils stored in museum collections. The bones, which date from about 10.5 million to 16 million years ago, preserve valuable clues about encounters between predators and prey.
In particular, the scientists looked for bite marks and tooth marks on the fossilized remains of herbivores. Such injuries are especially useful because they provide direct evidence that two animals interacted, rather than simply showing that they lived in the same place.
The researchers found that marks likely made by Purussaurus appeared frequently on the fossils. This suggests that the giant crocodylian was not simply an occasional hunter but one of the dominant predators in the ecosystem.
Its influence may even have extended beyond individual kills. By regularly hunting large herbivores, Purussaurus and other giant crocodylians may have helped control their populations and shape the entire food web.
Millions of years before modern South America took shape, its tropical wetlands may therefore have belonged to the crocodylians—giant predators powerful enough to rule both the water and the food chain.
