Australia may be famous for its unusual and dangerous wildlife, but five million years ago scientists say things would have been even stranger.
Giant kangaroos, some of which are more than twice the size of a human, roamed the country for millions of years, a new study has found.
Researchers at Flinders University have discovered three new species of giant fossil kangaroos that ranged from the deserts of Australia to the jungles of New Guinea.
The largest species, Protenmodon viator, weighed up to 170 kg (375 lb) and would have traveled across central Australia on its long limbs.
Dr Isaac Kerr, lead author of the study, says: “Live kangaroos are already extraordinary animals, so it is surprising to think what these peculiar giant kangaroos could have been up to.”
Scientists have discovered that giant kangaroos twice the size of a human would have roamed the arid heart of Australia five million years ago
Scientists have discovered three new species of giant kangaroos that lived in Australia five million years ago. This artist’s impression shows two of these species, Protemnodon anak (top) and Protemnodon tumbuna (bottom).
These prehistoric roosters would have looked much like a modern gray kangaroo, although stockier and more muscular.
Researchers believe they emerged about five million years ago and became extinct about 40,000 years ago.
The smallest of these ancient kangaroos would have weighed around 50 kg (110 lb), about the same size as a modern eastern gray.
The largest species would be about twice the size of an adult male red kangaroo, which can reach up to 1.8 m (5 ft 10 ft) tall.
Unusually, although the three new species are members of the same family, they would all have lived very different lives.
The fossil record reveals that these closely related species were especially adapted to their unique environments and would even have jumped differently.
Dr Kerr said: “Different species of Protemnodon are now known to have inhabited a wide range of habitats, from arid central Australia to the forested, rainfall-rich mountains of Tasmania and New Guinea.”
Protemnodon Viator (pictured) would have been the largest of the ancient kangaroos, weighing up to 170 kg (375 lb). This almost complete skeleton shows how long his legs would have been.
Ancient kangaroos would have been twice the size of an adult male red kangaroo (pictured), which may be taller than some humans at 1.8m tall.
The giant Protemnodon viator takes its name from the Latin meaning “walker” due to its long legs that would have allowed it to jump quickly and efficiently.
However, of the four Protemnodon now known to science, only one was truly bipedal.
Researchers say the others would have moved like a modern Quokka, mainly hopping on all fours and only occasionally jumping.
Dr Kerr says: “A large but robust and thick-boned kangaroo was probably moving quite slowly and inefficiently.”
“He may have jumped only on rare occasions, perhaps only when startled.”
Protemnodon dowsonae, the third new species, would have been a medium-speed jumper, although the few fossils make the life of this animal more of a mystery.
Not all ancient kangaroos would have jumped, scientists say most would have jumped on all fours like a quokka (pictured)
The first specimens of the Protemnodon species were discovered in 1875 by Sir Richard Owen, the Victorian scientist who coined the term dinosaur.
By looking at the fossil teeth, Owen concluded that there were six different species of Protemnodon.
However, only one of the species identified by Owen, Protemnodon anak, remains scientifically recognized.
The difficulty in evaluating these ancient kangaroos comes from the fact that their bones are often found in isolation, making complete skeletons extremely rare.
This only changed after a series of complete fossils were discovered in Lake Callanbonna in South Australia in 2013, 1018 and 2019.
Dr Isaac Kerr, lead author of the study (pictured), analyzed more than 800 different kangaroo fossils in four countries to identify the new species.
Protemnodon fossils are common but it is rare to find a complete skeleton. This image shows two volunteers excavating the largest known kangaroo fossil in Lake Callabonna, Australia.
To identify the new species, Dr Kerr traveled to 14 museums in four countries, photographing and scanning more than 800 specimens.
By evaluating “virtually every piece of Protemnodon in existence,” Dr. Kerr and his colleagues were able to identify the new species’ distinctive traits and adaptations.
The researchers hope this study will help future paleontologists more easily study ancient kangaroos.
Their discoveries could even help explain why these giant species became extinct while the gray and red kangaroo continued to thrive.
Professor Gavin Prideaux, co-author of the study, added: “Fossils of this genus are widespread and found regularly, but most of the time there is no way to be sure which species you are looking at.”
“This study may help researchers feel more confident when working with Protemnodon.”