Australia's (now-extinct) giant kangaroos packed one hell of a powerful bite. That's according to Rex Mitchell at the University of Arkansas, US, who compares this ancient beast's capacity for high-performance crushing to that of today's panda in the journal PLOS ONE.
"The skull of the extinct kangaroo studied here differs from those of today's kangaroos in many of the ways a giant panda's skull differs from other bears," Mitchell said in a statement.
"So, it seems that the strange skull of this kangaroo was, in a functional sense, less like a modern-day kangaroo's and more like a giant panda's."
The biomechanics of the giant roo's jaw was likely an adaptation to the climate, which allowed animals to eat tough, poor-quality vegetation if droughts or glacial periods meant their preferred food options were in short supply.
Short-faced kangaroos walked (not hopped) around Australia more than 40,000 years ago and include the largest kangaroo species ever discovered: the Procoptodon goliah, which could weigh more than 180 kilograms (400 pounds) and stood at 2 meters (6.5 feet) tall. Today's red kangaroos fall just shy of this number averaging around 1.5 meters (5 feet), although some bucks – see, for example, Roger the Internet-famous kanga – can reach 2 meters or more. They are also lither and less robust than their more muscular predecessors.
For the study, Mitchell used computed tomography scans to build three-dimensional models of the skull from a species of giant kangaroo called Simosthenurus occidentalis, which he then used to carry out bite simulations. During the simulations, Mitchell measured the resulting forces at the jaw joints and biting teeth, and the stress across the skull, comparing the results to those collected from models of a koala.
He found the shape of the skull boosted the efficiency of the biomechanical movements involved in biting, allowing the animal to withstand strong forces while biting and as such, helping it chow down on tougher vegetation like shrubs, trees, twigs, and older leaves. This is less like the feeding habits of today's kangaroos with their diet of grasses and more akin to koalas (who subsist solely on eucalyptus) or giant pandas, who munch on bamboo.
The short face, large teeth, and broad attachment sites for biting muscles found in the skulls of these kangaroos and the giant panda are an example of convergent evolution, said Mitchell. It is likely these features evolved in both to benefit similar feeding behaviors.