Super-muscular 374-pound kangaroos once thumped around Australia and New Guinea

Earth used to be absolutely crawling with more megafauna. The fossil record is full of enormous birds like New Zealand’s Heracles inexpectatus, giant lemurs from Madagascar, large marine reptiles that would put today’s sea snakes to shame. Paleontologists have now found evidence of three unusual new species of giant fossil kangaroo in present day Australia and New Guinea. The creatures are described in a study published April 14 in the journal Megataxa and indicate that these species were likely much more diverse in terms of shape, range of habitat, and hopping method.

“Living kangaroos are already such remarkable animals, so it’s amazing to think what these peculiar giant kangaroos could have been getting up to,” study co-author and Flinders University PhD student Isaac Kerr said in a statement.

An artist’s impression of the newly described fossil species Protemnodon viator and its relative Protemnodon anak, compared at scale to the living red kangaroo and eastern gray kangaroo. CREDIT: Traci Klarenbeek, 2024.

Meet the giant kangaroos

The three new species belong to an extinct genus of giant kangaroos called Protemnodon that lived from five million to about 40,000 years ago. They would have looked somewhat similar to modern gray kangaroos, but were generally more squat and muscular. Some species were roughly 110 pounds, but others were up to twice as large as today’s biggest living kangaroos.

Protemnodon fossils are fairly common across Australia, but they have historically been found as individual bones instead of in complete skeletons. This has made it difficult for scientists to determine just how many species there were and how they differed in geographic range, movement, and size.

[Related: What prehistoric poop reveals about extinct giant animals.]

“The fossils of this genus are widespread and they’re found regularly, but more often than not you have no way of being certain which species you’re looking at,” study co-author and Flinders University paleontologist Gavin Prideaux said in a statement.

For this study, the team was able to use multiple complete fossilized kangaroo skeletons from Lake Callabonna in South Australia, which may help give scientists a more clear picture of these giant kangaroos. Researchers also reviewed all known species of Protemnodon and found that they were all quite different from one another. The animals also adapted to live in different environments and even had different methods of hopping.

One very heavy, wayfaring kangaroo

One of the new species is named Protemnodon viator. The word viator means ‘traveler’ or ‘wayfarer’ in Latin. This wandering marsupial was also much bigger than other known giant kangaroos at weighing up to 374 pounds. According to the team, this is roughly twice as much as the largest living male red kangaroos.

A near-complete fossil skeleton of the extinct giant kangaroo Protemnodon viator from Lake Callabonna, missing just a few bones from the hand, foot, and tail. CREDIT: Isaac A. R. Kerr

Protemnodon viator was also likely well-adapted to its arid central Australian habitat. It lived in a smaller geographic area than the red kangaroos of today. It was also long-limbed and could hop quickly and efficiently.

A ‘robust’ creature and a swamp wallaby-like kangaroo

Another of the new species is named Protemnodon mamkurra and it connects the paleontologists of today with a famous scientist of the past. British paleontologist and naturalist Sir Richard Owen famously coined the term ‘dinosaur’ in 1842, but also described the first species of Protemnodon in 1874.

When he first found these giant kangaroo fossils, he followed a common scientific approach at the time. He mainly focused on fossilized teeth, seeing slight differences between the teeth of his specimens. He ultimately described six species of Protemnodon and further study chipped away at some of Owen’s early descriptions. He also suggested that some or all Protemnodon have four legs, While not all of them do, this study agrees that one of his species–Protemnodon anak–likely did have four legs.

[Related: Giant beasts once roamed Madagascar. What happened to them?]

“However, our study suggests that this is true of only three or four species of Protemnodon, which may have moved something like a quokka or potoroo–that is bounding on four legs at times, and hopping on two legs at others,” Kerr said. “The newly described Protemnodon mamkurra is likely one of these. A large but thick-boned and robust kangaroo, it was probably fairly slow-moving and inefficient. It may have hopped only rarely, perhaps just when startled.”

The best of these fossil species comes from the Green Waterhole Cave in southeastern Australia, on the land of the Boandik people. The species name mamkurra, means ‘great kangaroo’ and was chosen by Boandik elders and language experts in the Burrandies Corporation.

An artist’s reconstruction of the extinct kangaroos Protemnodon anak (upper) and Protemnodon tumbuna (lower). Despite being closely related, the two were quite different animals in terms of their habitat and their method of hopping. CREDIT: Peter Schouten (year unknown).

According to Kerr, it is unusual for a single genus of kangaroo to live in such varied environments. “For example, the different species of Protemnodon are now known to have inhabited a broad range of habitats, from arid central Australia into the high-rainfall, forested mountains of Tasmania and New Guinea.”

The third new species is named Protemnodon dawsonae. It is known from fewer fossils than the other two, so it is more of a mystery. The team believes it was likely a moderate speed hopper and potentially similar to the living swamp wallaby. It was named in honor of Australian paleontologist Lyndall Dawson.

While most species became extinct about 40,000 years ago on mainland Australia, they potentially lived longer in New Guinea and Tasmania. Future studies could shed more light on their extinction, as it is still an enduring paleontological mystery.