Giant kangaroo twice the size of a human roamed Australia 5 million years ago, study reveals

Australia might be famous for its unusual and dangerous wildlife, but five million years ago scientists say things would have been even stranger. 

Giant kangaroos - some more than twice the size of a human - roamed the country for millions of years, a new study has found.

Researchers from Flinders University have uncovered three new species of giant fossil kangaroo which spread from the deserts of Australia to the jungles of New Guinea. 

The largest species, Protenmodon viator, weighed up to 170kg (375 lbs) and would have travelled central Australia on its long limbs. 

Dr Isaac Kerr, lead author of the study, says: 'Living kangaroos are already such remarkable animals, so it's amazing to think what these peculiar giant kangaroos could have been getting 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 kangaroo that lived in Australia five million years ago. This artist's impression shows two of these species, Protemnodon anak (upper) and Protemnodon tumbuna (lower)

These prehistoric roos would have looked much like a modern grey kangaroo, although more squat and muscular. 

The researchers believe they emerged around five million years ago and went extinct sometime around 40,000 years ago. 

The smallest of these ancient kangaroos would have been around 50kg (110 lbs), about the same size as a modern-day Eastern Grey.

The largest species would be about twice as large as an adult male red kangaroo, which can reach up to 1.8m (5ft 10') tall.

Unusually, although the three new species are all members of the same family, they would have all lived very different lives. 

The fossil record reveals that these closely related species were adapted specially to their unique environments and would have even hopped differently.

Dr Kerr said: '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.'

Protemnodon Viator (pictured) would have been the biggest of the ancient kangaroos, growing up to 170kg (375 lbs). This almost complete skeleton shows how long its legs would have been 

The ancient kangaroos would have been twice the size of an adult male red kangaroo (pictured) which can be taller than some humans at 1.8m in height 

The giant Protemnodon viator takes its name from the Latin for 'wayfarer' due to its long legs which would have let it hop quickly and efficiently.

However, out of the four Protemnodon now known to science, only one was truly bipedal. 

The researchers say that the others would have moved like a modern Quokka, mostly bounding on four legs and only occasionally hopping.

Dr Kerr says: '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.'

Protemnodon dowsonae, the third new species, would have been a mid-speed hopper - although scarce fossils make this animal's life more of a mystery. 

Not all of the ancient kangaroos would have hopped, the scientists say that most would have bounded on all fours like a quokka (pictured) 

The first specimens of Protemnodon species were discovered as far back as 1875 by Sir Richard Owen, the Victorian scientist who coined the term dinosaur.

By looking at fossil teeth, Owen came to the conclusion that there were six distinct species of Protemnodon.

However, only one of Owen's identified species, Protemnodon anak, is still scientifically recognised.

The difficulty in assessing these ancient kangaroos comes from the fact that their bones are often found in isolation, making full skeletons extremely rare. 

This only changed after a series of full fossils were discovered in Lake Callanbonna in South Australia in 2013, 1018, and 2019. 

Dr Dr Isaac Kerr, lead author of the study (pictured) analysed more than 800 different kangaroo fossils across four countries to identify the new species 

Protemnodon fossils are common but it is rare to find a full skeleton. This image shows two volunteers excavating the largest known kangaroo fossil at Lake Callabonna, Australia

To identify the new species, Dr Kerr travelled to 14 museums in four countries, photographing and scanning over 800 specimens.  

By assessing 'just about every piece of Protemnodon there is', Dr Kerr and his colleagues were able to identify the distinctive traits and adaptations of the new species. 

The researchers hope that this study will help future palaeontologists study ancient kangaroos more easily.

Their discoveries could even help explain why these giant species went extinct while the grey and red kangaroo have continued to thrive.

Professor Gavin Prideaux, co-author of the study, added: '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. 

'This study may help researchers feel more confident when working with Protemnodon.'