Prehistoric giant kangaroo as big as a grown man had a powerful bite

© N. Tamura
Artistic reconstitution of the short-faced kangaroo, Simosthenurus occidentalis.

Researcher reveals fascinating new details about a group of giant prehistoric kangaroos, according to a study published in the open access journal PLOS ONE.

According to the scientist, the skulls of these so-called "sthenurine" kangaroos were highly specialized and provided the animals with a powerful bite that allowed them to eat tough foods.

Unlike their modern counterparts, these kangaroos probably walked on two legs, much like humans, rather than jumping to move. This family of animals – sometimes referred to as "short-legged kangaroos" – died out in the late Upper Pleistocene (about 126,000 to 5,000 years ago).

"Sthenurine kangaroos are an entirely extinct group of robust marsupial herbivores that appeared in the Miocene period. [around 23 to 5.3 million years ago] and prolifically diverse during the Australian Ice Age, "said study author, D. Rex Mitchell, of the University of Arkansas Newsweek.

"There are currently 26 species spread over 6 genera [groups of species] known to all of Australia, including the largest kangaroo ever to have existed, Procopton goliah, "he says. In general, they would have looked very different from modern-day kangaroos, with thicker bodies, long, muscular arms with extended fingers, often with one big toe on each foot and a box-like shape. heads that have been shaped more like a koala. "

Sthenurine kangaroos include heavily constructed skulls, short snouts, jaws and large teeth, which scientists had previously suggested was an indication that they were eating tough foods such as leaves, stems and stools. ripe branches.

To determine if this was the case, Mitchell tested the idea that the construction of the skulls of these kangaroos should be strong enough to cope with the powerful forces generated by their bites.

To do this, Mitchell digitally recreated the skull of a species of sthenurine kangaroo known as Simosthenurus occidentalis which ran from what is today Australia to the Upper Pleistocene until its extinction, about 42,000 years ago.

"A study that I published in January looked at this species with the help of a form analysis and biomechanical simulations," Mitchell said. "The results showed that the skull of the extinct kangaroo was, among a range of marsupial herbivores tested, of a form close to that of a koala."

However, this kangaroo was also distinguished from all the species to which it was compared by a deeper skull, a broad forehead and enormous cheekbones. The purpose of the last study was to determine the significance of these enhanced skull bone characteristics and to determine if they allowed specialized eating behaviors.

"Simosthenurus occidentalis is a well-represented species of stenurine, with remains found in most of the southern half of Australia. The species has become quite large, able to stand as tall as an adult and estimated at about 118 kilograms. [260 pounds]- about 30 kilos more than the biggest kangaroos today. This makes it an interesting species to study, as a representative of the extinct megafauna of Australia, "he said.

Using the numerical model, which was generated from the skull tomodensitograms of a S. occidentalis specimen, Mitchell simulated the bite of the animal and compared it to that of koalas.

"Simulations of molar and premolar bites were done to examine the distribution of forces on the skull," he said. "Given that the koala is the modern species whose skull shape is the most similar, the results were compared to models of a koala subjected to the same simulations."

Related Slideshow – Missing Species in our lifetime (provided by Photo Services)

These simulations showed that the cheekbones of S. occidentalis large, sustained muscles that prevent dislocation of the jaw when the animal uses its powerful bite.

"It is interesting to note that short-faced kangaroo models presented a much higher risk of injury than koala models when biting back teeth," Mitchell said. "This is because his teeth were much larger and extended further back towards the jaw joints." This greatly increased the strength of the animal to bite, but also increased the risk of dislocation of the jawbone. jaw when he was biting. "

"However, I found that an enlargement of a muscle located on the inner surface of its huge cheekbones would help reduce this risk," he said. This muscle is also enlarged in the giant panda, another animal of similar size that feeds on a thick and resistant vegetation such as bamboo.

In addition, the scientist found that the bones of the front and roof of the skull provided sufficient structural support to withstand the torsional forces that would have been generated during these bites.

"This study found that the short-faced kangaroo model could withstand twisting much more effectively than koala during such bites," Mitchell said. "His deep skull and broad forehead could spread stress more evenly, preventing excessive torsion and protecting him from damage."

This finding is consistent with previous suggestions for short-faced kangaroos that the hardest and thickest vegetation that could have been eaten, such as woody twigs and branches of trees and shrubs , could have been introduced directly into his premolars and molars to be crushed or broken. a part. Such actions would seem similar to the way giant pandas crush bamboo, "he said.

Taken together, these results led Mitchell to conclude that the kangaroos of the stenurine group were able to produce powerful stings through these adaptations, allowing them to eat hard foods that other species were not able to consume.

"The research supports the hypothesis that at least some short-face kangaroos may persist on low-grade, thick, woody vegetation during periods of low productivity, such as during droughts, extended ice ages, and long periods of time. associated continental drying up, "he said. . "The ability to consume parts of plants that other herbivores of the time could not offer them a competitive advantage in difficult times."

In this direction, S. occidentalis is similar to modern animals such as the giant panda, which also eats tough foods in the form of bamboo.

"The similarities between the skulls of this kangaroo and the giant panda provide a good example of convergent evolution, in which similar features of the skull have independently evolved to fulfill potentially similar functions," Mitchell said.