New Research Postulates Giant, Prehistoric Kangaroos Could Still Hop
Researchers studying the fossilised remains of giant, prehistoric kangaroos have concluded that even marsupials weighing more than two hundred kilograms were not too big to hop. This new study, published in the academic journal “Scientific Reports” challenges the long-held view that these giants were walkers rather than hoppers. The research team examined fossils of short-faced kangaroos (Sthenurinae). During the Pleistocene some of these kangaroos evolved giant, robust forms. Their method of locomotion remains controversial. Did humans encounter walking giant short-faced kangaroos or did they witness a sthenurine hopping?
Cast of a sthenurine skeleton (Sthenurus occidentalis) in the South Australian Museum. Picture credit Megan Jones.
Picture credit: Megan Jones
A Sthenurine Hopping Hypothesis
The Sthenurinae are a subfamily of the Macropodidae. The Macropodidae is a large family of marsupials that includes kangaroos, wallabies and their relatives. The largest extant kangaroo is the red kangaroo (Osphranter rufus). Males can weigh as much as ninety kilograms and stand 1.6 metres tall. They are the largest terrestrial mammal native to Australia and the largest living marsupial. However, during the Pleistocene, much larger kangaroos evolved. For example, whilst small, wallaby-sized sthenurines are known, other taxa were much larger than living kangaroos. The sthenurine Procoptodon goliah is thought to be the biggest kangaroo that ever existed. Males stood around two metres tall and weighed perhaps as much as two hundred and forty kilograms.
Reconstruction of a giant short-faced kangaroo (sthenurine) hopping. Picture credit: Megan Jones.
Picture credit: Megan Jones
Earlier studies suggested that hopping would become mechanically impossible above a body weight of a hundred and fifty kilograms. Those conclusions were largely based on studies of extant kangaroo skeletons. The anatomy of modern kangaroos was simply scaled up.
To read a blog post from 2014 that looked at evidence for walking locomotion in largest members of the Sthenurinae: Giant Kangaroos Made for Walking.
This new study involved scientists from The University of Manchester, in collaboration with the University of Bristol and the University of Melbourne. These researchers took a different approach. Measurements taken from the skeletons of extant species were compared with the fossil remains of extinct species. The researchers conclude that giant kangaroos may have been capable of hopping. Indeed, early Australians could have observed a sthenurine hopping.
Lead Researcher Megan Jones, (The University of Manchester) explained:
“Previous estimates were based on simply scaling up modern kangaroos, which may mean we miss crucial anatomical differences. Our findings show that these animals weren’t just larger versions of today’s kangaroos, they were built differently, in ways that helped them manage their enormous size.”
Examining the Two Limiting Factors for Hopping
The research team examined two potential limiting factors for hopping, the strength of the foot bones and the ability of the ankle to anchor the powerful tendons that power hopping. The analysis demonstrated that giant, short-faced kangaroos had shorter, robust foot bones capable of withstanding landing forces and their heel bones were broad enough to support much thicker tendons.
However, Pleistocene giant kangaroos probably did not bounce across the landscape like modern red kangaroos.
Co-author Dr Katrina Jones (Bristol University), stated:
“Thicker tendons are safer, but they store less elastic energy. This likely made giant kangaroos slower and less efficient hoppers, better suited to short bursts of movement rather than long-distance travel. But hopping does not have to be extremely energy efficient to be useful, these animals probably used their hopping ability to cross rough ground quickly or to escape danger.”
Heel bone (calcaneum) of the largest kangaroo species, Procoptodon goliah. P. goliah stood over two metres tall and had an estimated body mass of 240 kilograms, almost three times the size of the largest living kangaroos. Picture credit: Megan Jones/UCMP.
Picture credit: Megan Jones/UCMP
A Range of Locomotion Strategies Identified
The fossil analysis also reveals a range of locomotion strategies adopted by extinct kangaroos. Some giants may have mixed hopping with other forms of movement, including bipedal walking and moving around on all fours. Sthenurine hopping may have just been one part of a broader “movement repertoire”. The research implies different ecological niches for prehistoric kangaroos.
Fellow researcher and co-author Dr Robert Nudds, Senior Lecturer in Evolution, Infection and Genomics at The University of Manchester commented:
“Our findings contribute to the notion that kangaroos had a broader ecological diversity in prehistoric Australia than we find today, with some large species grazers like modern kangaroos while others were browsers – an ecological niche not seen in today’s large kangaroos.”
The research provides the most comprehensive assessment to date of the mechanical feasibility of hopping in giant extinct kangaroos.
Everything Dinosaur acknowledges the assistance of a media release from The University of Manchester in the compilation of this article.
The multi-award-winning Everything Dinosaur website: Models and Replicas of Prehistoric Mammals.
