South America during the Miocene was a frightening place. More than ten million years ago, a vast lake covered much of the continent, home to giant turtles and crocodylians.
On the lake's shores hunted a wide range of predators, including anacondas, saber-toothed mammals, flightless "terror birds" and sebecids — terrestrial relatives of crocodylians.
A recent study shows that crocodylians were in fact the most significant group of predators in this habitat.
"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."
Bite traces reveal the predator
On the lake's shores lived a great variety of herbivores: giant ground sloths, glyptodonts — relatives of armadillos — and several groups of ungulates, such as astrapotheres ("lightning beasts") and toxodontids. The ungulates of this era could weigh well over a tonne.
But the predators were giants too. The largest predator of the time was a seven-metre-long, 1,800-kilogram crocodylian, Purussaurus neivensis, a relative of modern caimans. At the top of the food chain, it may even have influenced the size of herbivore populations, the new study suggests.
The research is based on the analysis of fossils held in museum collections. Bite and tooth marks left by predators on herbivore fossils are the only direct evidence of interactions between species. The fossils examined were between 10.5 and 16 million years old.
"The frequency of marks likely made by Purussaurus suggests that it was an important predator in these tropical ecosystems," Wilson comments.
The study was published in Journal of Vertebrate Paleontology
