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Giant Crocodylians Dominated South America’s Miocene Food Chain, Study Finds

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South America was home to a formidable collection of predators more than 10 million years ago, when a vast lake covered much of the continent and supported giant turtles, crocodylians and an extraordinary range of prey.

New research suggests that crocodylians, rather than mammals or other land-based predators, were the most important predators in these ancient ecosystems, particularly when it came to hunting large animals.

The findings are based on an analysis of fossil remains dating from about 10.5 million to 16 million years ago. Researchers examined bite and tooth marks preserved on herbivore fossils, providing direct evidence of interactions between predators and their prey.

A Seven-Metre Predator at the Top

The Miocene lake system supported an abundance of large herbivores, including giant ground sloths, glyptodonts — ancient relatives of modern armadillos — and several groups of large hoofed mammals.

Some of these animals, including astrapotheres and toxodontids, could weigh more than a tonne.

They shared the ecosystem with an equally imposing group of predators. Among the most formidable was Purussaurus neivensis, a giant crocodylian related to modern caimans. It could reach about seven metres in length and weigh as much as 1,800 kilograms.

Other predators included anacondas, saber-toothed mammals, flightless terror birds and sebecids, which were terrestrial relatives of modern crocodylians.

Despite this diversity, the study indicates that crocodylians were particularly important predators in the ancient ecosystem.

Fossil Bite Marks Tell the Story

Researchers from the University of Helsinki studied bite and tooth marks preserved on fossilized remains of herbivores. Such marks can reveal which predators attacked or scavenged animals, even when the predator itself is not preserved alongside its potential prey.

The frequency and characteristics of marks attributed to Purussaurus suggest that the giant crocodylian played a major role in the tropical food web.

Oscar Wilson, a postdoctoral researcher at the University of Helsinki, said the abundance of prey was so great that mammalian predators alone would not have been capable of consuming it all.

The evidence indicates that crocodylians filled an important ecological role, particularly by targeting large-bodied prey.

The findings also raise the possibility that Purussaurus influenced herbivore populations. As one of the largest predators in the ecosystem, the giant crocodylian may have exerted substantial pressure on large herbivores and helped shape the structure of the ancient food web.

The study provides a glimpse into an ecosystem where enormous predators and prey lived alongside one another — and where giant crocodylians may have occupied a position closer to the top of the food chain than previously recognized.

 

Also Read:

Crocodiles Set to Face Extinction, Says Australian Researcher

‘Nagatitan’: Southeast Asia’s biggest long-necked dinosaur discovered

 

Crocodiles Set to Face Extinction, Says Australian Researcher

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An estuarine crocodile, also known as a “saltie”.

Many of the world’s 27 species of crocodylians will soon be either totally or locally extinct due to human population expansion and intensive land-use for agriculture depleting the water bodies, which provide succour to crocs, said a University of Queensland researcher.

Emeritus Professor Gordon Grigg of UQ says the fact that these reptiles had survived millions of years was no good owing to current rate of human expansion and encroachment of natural resources. “The current human population level and its magnitude and rate of resource consumption are unprecedented,” Professor Grigg said.

Only those crocs living in remote wetland habitats in which humans see no benefit may survive into the future, he said. Some crocodylians might have already become extinct if not for active conservation management undertaken in the second half of the 20th Century.

“For some species, the incentive for conserving them has been the commercial value of their hides, but that is dependent upon its use in high fashion garments and accessories, and that is a somewhat fragile foundation,” he said.

On flip side, the rising temperatures and sea levels may turn a more positive note for crocodylians, as it may create more habitat that will be suitable for any species to survive the human onslaught, he said wryly.

The largest living crocodiles, the estuarine or saltwater crocodile (Crocodylus porosus), are found in Northern Australia and can grow to six metres and weigh more than 900 kilograms.

Professor Grigg said estuarine crocodiles, also known as Indo-Pacific crocodiles or “salties”, were one of the luckier species because human populations across Australia’s north were unlikely to increase significantly in the next few decades.  They might be among the survivors.

Professor Grigg and illustrator and biologist David Kirshner, in their recent book, Biology and Evolution of Crocodylians, reviewed the biology of the crocodiles, alligators, caimans and gharials, and also discusses the great diversity of their gigantic extinct ancestors, some of which were probably warm-blooded.