Researchers Chew Over a Prehistoric Bear’s Diet

Of all the bears to come and go during the group’s 23 million year old history, none had a bite more powerful than Agriotherium africanum – a ursid as large as today’s grizzly and polar bears that roamed Africa during the latest Miocene and earliest Pliocene epochs. In a new Journal of Zoology paper by C.C. Oldfield, Colin McHenry, and colleagues, virtual models used to run bite tests predicted that the fossil bear could bring its canines down with 4566 Newtons of force – the equivalent of about one thousand pounds of pressure. The question is why this huge extinct bear required such a powerful bite.

For some prehistoric creatures, it isn’t difficult to envision their feeding habits. Tyrannosaurus rex undoubtedly clamped its heavily-fanged jaws on struggling Edmontosaurus and rotting Triceratopsstruggling Edmontosaurus and rotting Triceratopsstruggling Edmontosaurus and rotting Triceratopsstruggling Edmontosaurus and rotting Triceratops, and so the dinosaur’s overwhelming bite strength makes sense given its hypercarnivorous lifestyle. But the connection between skull anatomy, bite force, and diet isn’t always so clear.

The skull of Agriotherium africanum looks like that of a dedicated carnivore. Much like Arctodus – a similarly-proportioned but distantly-related bear from the Pleistocene of North America – Agriotherium had a relatively broad, deep skull well-suited to handling the stresses and strains created by large, struggling prey. Then again, the same suite of features could have just as readily been employed to dismember carcasses or crunch tough plants, and some researchers have argued that Agriotherium, Arctodus, and similar bears were omnivores that often fed on carrion rather than chasing down large prey.

As Oldfield and co-authors point out, the remarkably high bite force Agriotherium brought to bear doesn’t allow us to distinguish between the hunting and scavenging alternatives. Having a powerful bite is just as useful to an active predator as to a saprovore. And modern bears only complicate efforts to reconstruct the lifestyle of Agriotherium.

When the researchers investigated the mechanical properties of skulls representing a giant panda, a brown bear, an American black bear, an Asian black bear, and a polar bear, there was no indication that bite force, alone, predicted carnivory. Quite the contrary. The mostly-herbivorous giant panda had the strongest bite force for its size, while the hypercarnivorous polar bear had among the lowest proportional bite force. In fact, Oldfield and collaborators deemed the polar bear as “among the poorest performers” in terms of being able to handle the stresses involved with killing and consuming large prey. Maybe this is because the polar bear eats a great deal of blubber from prey that can’t put up much of a fight on land, the researchers suggest, but the main point is that there is not a simple connection between being a predator and having a strong bite.

Despite the similarities between the Agriotherium and giant panda models, though, Oldfield and collaborators don’t think that the fossil bear was an herbivore. The cheek teeth of Agriotherium are better suited to slicing than to grinding vegetation, hinting that the bear regularly dined on flesh. What remains unknown was how Agriotherium acquired that meat. “A. africanum was more than capable of dispatching very large vertebrate prey,” the researchers write, “but this does not mean that it did.” Like so many debates in paleontology, we are left trying to untangle what an animal was capable of from what that creature actually did.

Reference:

Figueirido, B., Pérez-Claros, J., Torregrosa, V., Martín-Serra, A., Palmqvist, P. 2010. Demythologizing Arctodus simus, the ‘Short-Faced’ long-legged and predaceous bear that never was Journal of Vertebrate Paleontology, 30 (1), 262-275 : 10.1080/02724630903416027

Oldfield, C., McHenry, C., Clausen, P., Chamoli, U., Parr, W. Stynder, D., Wroe, S. 2012. Finite element analysis of ursid cranial mechanics and the prediction of feeding behaviors in the extinct giant Agriotherium africanumFinite element analysis of ursid cranial mechanics and the prediction of feeding behaviors in the extinct giant Agriotherium africanum. Journal of Zoology, 286. 163-170