Chuck Bednar for redOrbit.com – @BednarChuck
Determining if a prehistoric creature was a carnivore or a plant-eater isn’t as easy as comparing its skull shape and tooth patterns to modern animals with similar features, researchers from the American Museum of Natural History explain in a new PLOS One study.
Rather, using models and tests on living species, John J. Flynn, the Museum’s Frick Curator of Fossil Mammals, and his colleagues found that there is a complex link between animal diets and skull biomechanics, and that a creature’s ancestry plays a larger-than-expected role.
“Traditionally, when we looked at a fossilized skull with pointy piercing teeth and sharp slicing blades, we assumed that it was primarily a meat eater, but that simplistic line of thinking doesn’t always hold true,” he said in a statement. “We’ve found that diet can be linked to a number of factors – skull size, biomechanical attributes, and often, most importantly, the species’ position in the tree of life.”
This image shows the skulls of the different species the researchers studied along with biomechanical profiles, which were made by mapping each animal's bite force against skull stiffness. They found that ancestry has a strong influence on the models, with closely related animals like leopards and mongooses grouping together, but also that predications about diet can be made based on the shape of the individual biomechanical profiles. (Credit: Copyright AMNH/Z.-J. Tseng)
Flynn and his colleague Z. Jack Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the Museum’s Division of Paleontology, looked at the link between the shape and function of five different modern carnivore species, including meat-eating “hypercarnivores” like wolves and leopards and more omnivorous “generalists” such as skunks and raccoons.
Creating models and applying them to extinct carnivores
First, they mapped the force of an animal’s bite against the stiffness of its skull, and much to their surprise they found that creatures that had similar diets and biomechanical demands (such as the wolf and leopard) did not match up exactly. Rather, the leopard and mongoose were found to have a closer bond because the two creatures are more in an evolutionary sense, even though they now have vastly different dietary preferences and feeding strategies.
Once they took into account the impact that ancestry and skull size had on their models, though, Flynn and Tseng said that they were still able to use biomechanics to distinguish generalists from hypercarnivores. They did so by focusing on the row of teeth where the skull is strongest.
Skulls of dedicated meat eaters are stiffest when hunting with the front teeth and slicing/crushing with the back ones, while the skulls of generalists show incrementally increasing stiffness when biting sequentially from the front to the back of the tooth row, the researchers explained.
Flynn and Tseng then applied this revised model to a pair of extinct creatures: a predatory mammal known as Thinocyon velox and an early carnivore called Oodectes herpestoides. They discovered that the former had a unique hypercarnivorous feeding style which featured skull strength at both the front teeth for prey capture and the back teeth for slicing and crushing, and the latter was a generalist that likely fed on small prey due to its relatively weak skull.
“Beyond feeding adaptations of extinct species, we also want to decipher how adaptations evolved using reconstructed ancestors of living and fossil forms,” explained Tseng. “We are applying similar types of skull shape and biomechanical analyses to reconstructed hypothetical ancestor skulls of Carnivora and their relatives to map out and better understand the long history of feeding adaptation of living top predators.”
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