A now-extinct Australian animal was even bigger than previously thought and had joints that are unique among mammals.

A weird species of ancient Australian marsupial had enormous claws, and elbows that were almost completely rigid — a characteristic found in no other mammal, living or extinct.

Large marsupials called palorchestids thrived in Australia for some 25 million years, until as recently as 50,000 years ago. Scientists long mistook them for ancient kangaroos, but eventually realized that these animals were more similar to horse-sized versions of wombats.

In an attempt to describe the appearance and movements of these little-known marsupials, Hazel Richards at Monash University in Clayton, Australia, and her colleagues examined the limbs of more than 60 fossil specimens from 3 species.

The team’s observations suggest that palorchestids were large creatures that could weigh more than one tonne. They had enormous claws that might have helped them to forage for shoots, twigs and leaves, and Palorchestes azael, the most abundant and latest-surviving species, had elbows that were almost completely fixed in a ‘bent’ position.

The authors hope to learn more about palorchestids as more fossils are unearthed or identified in museum collections.