Understanding extinct species diets requires greater understanding of the relationship between skull biomechanics and animals ancestry than previously thought, according to a new study. 

The diet of long-extinct animals may be inferred by using modern animals with similar skull shapes and tooth patterns as models, but that would not mean that diet is the main factor influencing skull shape and biomechanics.  Neanderthals did not have a chin, nor does any other animal, but that is not due to the modern human diet.

To understand whether these models might apply to living species, the authors of this study modeled the relationship between skull shape and function, i.e., bite efficiency against the stiffness of the animal's skull, of five different modern carnivore species, including meat-eating "hypercarnivore" specialists, such as wolves and leopards, and more omnivorous "generalists," such as mongoose and raccoons. 

The initial results showed that "animals with the same diets and biomechanical demands, like wolves and leopards--both hypercarnivores--were not linking together," lead author Jack Tseng said. "Instead, we saw a strong signal driven mostly by ancestry, where, for example, the leopard and the mongoose bind together because they're more closely related in an evolutionary context, although they have very different dietary preferences and feeding strategies."

Once the researchers accounted for the strong effects of ancestry and skull size on the models, hypercarnivores and generalists still could be distinguished based on biomechanics, in particular by looking at where along the tooth row the skull is strongest.

The researchers then applied this improved shape-function model to two extinct species: Thinocyon velox, a predatory mammal that was part of the now-extinct Creodont group, and Oodectes herpestoides, an early fossil predecessor of modern carnivores. They found that T. velox likely had a unique hypercarnivorous feeding style that allowed for skull strength at two places: prey capture with its front teeth, and powerful slicing and crushing with its back teeth. The biomechanical profile of O. herpestoides, meanwhile, suggests that it was a generalist, but compared to living relatives of similar body size, it might have fed on smaller prey because of its weaker skull.

Lead author John J. Flynn said, "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."

Citation: Tseng ZJ, Flynn JJ (2015) Are Cranial Biomechanical Simulation Data Linked to Known Diets in Extant Taxa? A Method for Applying Diet-Biomechanics Linkage Models to Infer Feeding Capability of Extinct Species. PLOS ONE 10(4): e0124020. doi:10.1371/journal.pone.0124020