Just like modern-day species of kangaroo, the now extinct sthenurines (Sthenurus stirlingi) lived in Australia, where they roamed for over 12.5 million years before they were totally wiped out of existence more than 30,000 years ago.
The "short-faced giant kangaroo," however, was three times the size of today's species. They stood over 10 feet tall and weighed over 529 pounds. A new study suggests that because of their colossal size, these giant marsupials did not move around the way the kangaroos of today hop at high speed and move at slower speed using their tail and two forelimbs.
In a study published in PLOS ONE on Oct. 15, researchers found evidence that sthenurines developed an upright posture that would have given them the ability to put one foot in front of the other. The finding suggests that these giant beasts did not likely hop but instead walked on two legs.
Christine Janis from the department of ecology and evolutionary biology at Brown University, Rhode Island and colleagues examined the bones of 144 living and extinct species of kangaroos, 71 of which were from sthenurines, to determine the probable size and function of the bones and muscles of each of the animals.
The researchers found that the bone structures of the giant kangaroos resembled those of humans who move by shifting their body weight from one side to another. Compared with modern species, the giant kangaroos had bigger hops and knees; their stabilized ankle joints would have allowed them to balance their weight over one leg at a time.
The researchers also noticed that the ill-fated kangaroos had stiff backs that could have limited their ability to bend their backs and support the weight of their bodies with their hands, if they used their four legs and tails just as kangaroos of today do. They also had shorter and less muscular tails, which would seem beneficial if used for pentapedal walking. This idea led the researchers to conclude that the anatomy of this enormous animal would have made it difficult for them to hop. These giant species may have, after all, weighed up to 550 pounds.
"Sthenurines lack the specialized features for fast hopping seen in macropodines and the differences in anatomy from the extant forms can be functionally related to locomotion bearing weight on one leg at a time," the researchers wrote.
Aside from their size and way of movement, the species did not also look so much as their modern cousins. The modern-day kangaroos are long-faced but these extinct beasts had short faces that resembled that of a rabbit.
