Millions of years ago, from the late Oligocene to the Late Pleistocene, giant marsupial beasts with strange, tapir-like heads roamed eastern Australia. Now, scientists have analyzed the limbs of these clawed giants, revealing more about what their bodies were like. Reporting their findings in PLOS ONE, the researchers conclude that some of these monstrous marsupials may have weighed over 1,000 kilograms (2,200 pounds), that’s five times heavier than a blue whale’s heart, in case you were wondering.
The team, led by Hazel Richards of Monash University, studied over 60 fossil specimens of palorchestid marsupials from different time periods to try to determine how their arms and legs evolved and how they were used. The researchers found that over the years, the animals’ appendages not only got larger, they got weirder too.
As they evolved, their arms gained muscle, making these herbivores particularly hench. This strength would have been perfect for grabbing or scraping at branches and leaves. Meanwhile, the biggest palorchestids had an arm feature not seen in any other mammal – they had immobile elbow joints stuck in place at a 100-degree angle. Their purpose? To create permanently flexed tools for collecting food, of course. Meanwhile, their feet were adorned with “knife-like” claws adapted for “slicing, clinging and raking”.
"There are many weird aspects to palorchestid anatomy, but for me the most fascinating are the forelimbs," Richards told IFLScience. "Their arm bones are super robust, and in some ways they resemble the forelimbs of digging animals like wombats. But palorchestid claws would be terrible at digging (like trying to dig with a chef's knife), and their elbows don't allow the movements necessary to do this anyway. To have an elbow unable to bend or straighten is totally unheard of in any other mammal, living or extinct, so I am interested in understanding how palorchestids used their arms and how they came to be so unusual."
Their strange, long faces, likened to those of today’s tapirs, suggest they were selective browsers, feeding on vegetation. Some scientists suggest that they may have fed on bark, occupying their own specific feeding niche, but we don’t know for sure.
"They may also have been able to rear up onto their back legs and use their clawed hands to dig into tree bark to bring their long tongue and nipping incisors closer to foliage higher up off the ground," said Richards.
The study marks the first time the limb morphology of these giants has been formally described, shedding light on a creature whose fossils are “exceptionally rare”. Meanwhile, the study concludes that palorchestids were significantly larger than we previously thought.
"We don't know exactly why palorchestids became so large, but this pattern of body size increase over time is seen across many different mammal, reptile, and bird lineages in Australia and across other continents," Richards explained.
The researchers note that most of Australia’s marsupial megafauna went extinct during the Late Pleistocene, most likely thanks to a combination of climate change and human activity. While the palorchestids are no longer roaming Australia, they will forever be remembered as one of the most bizarre groups of animals to inhabit the continent.
"This study has allowed us for the first time to appreciate just how huge these mega-marsupial palorchestids were, while also providing the first comprehensive view of a strange limb anatomy unprecedented in the mammalian world,” the researchers said in a statement. “This research reveals yet more about the diversity of unique large marsupials that once roamed Australia not so long ago."