Sthenurine kangaroos, also called “short-faced” kangaroos, are extinct now. But these marsupials lived in Australia around 42,000 years ago. And unlike modern kangaroos, they had short snouts, powerful jaws and teeth and skulls built for a tough, hefty diet.
Rex Mitchell, a researcher of feeding biomechanics and skull shape at the University of Arkansas, created a digital model of a skull belonging to one extinct species, Simosthenurus occidentalis, to test the bite force. His study published Wednesday in the journal PLOS ONE.
Previous research focused on the powerful jaws belonging to the species. Mitchell proposed that the skull would need to be fortified against the outcome of chewing tough, woody food with a strong bite force.
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With their short noses, they looked more like koalas in the face than modern kangaroos. These marsupial herbivores diverged from kangaroos and wallabies 15 million years ago. Today, their closest living relative is the banded-hair wallaby.
Simosthenurus occidentalis could weigh 260 pounds.
“They grew to their larger sizes independently of modern-day kangaroos,” Mitchell said. “They would have looked quite different to modern-day kangaroos — in general they had a more thick-set body, long muscular arms with long grasping fingers, many species had only one large toe on each foot, and some, including this species studied here, had box-shaped heads that looked more like a koala’s.”
Mitchell’s simulations using the digital skull showed that the cheekbones provided a foundation for muscles to prevent jaw dislocation and the front and roof of the skull created an arch to prevent any twisting during chewing.
A comparison of skulls shows similarities and differences.

A comparison of skulls shows similarities and differences.

Adapting to eat tough food helped the kangaroos survive, eating things that other species couldn’t. It’s similar to other modern species as well, Mitchell said.
“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. 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,” Mitchell said.
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Their shorter snout was also part of the adaptation. Mitchell’s previous research showed that the lack of a long snout allowed the kangaroo to use more efficient muscle force behind its bite.
The kangaroos would need to eat low-nutrition, tough foods during climate change. Unlike modern kangaroos, Simosthenurus didn’t graze on grass. Instead, it used its long arms to browse by reaching for leaves, twigs, tree branches and shrubs. When the climate was warmer and wetter, they probably had their choice of flowers, fruits and fresh leaves, Mitchell said.
“However, when glacial cycles kicked in and productivity dropped, an ability to consume less desirable browse, such as thicker, woodier branches, may have helped them to survive prolonged glacial periods,” Mitchell said. “Short-faced kangaroos could persist on thick and woody, poor-quality vegetation at times of low productivity, such as during droughts, and prolonged glacial periods and associated continental drying. The ability to consume parts of plants that other herbivores of the time could not would have offered them a competitive edge when times were tough.”
While there’s no directly known cause for their extinction, previous research has suggested that changes in climate and hunting by humans could have led to their eventual demise.