Not all kangaroo ancestors hopped as a means of locomotion

Contrary to popular belief, not all kangaroos have always hopped. That’s the surprising revelation from a detailed analysis by scientists from the University of Bristol and the University of Uppsala. 

Although we typically think of hopping as the signature move of kangaroos, the researchers assert that extinct kangaroos employed varied locomotion methods, from walking on two legs to traveling on all fours.

The findings, published in Alcheringa: An Australasian Journal of Palaeontology, challenge our traditional view of kangaroo evolution. We’re accustomed to associating kangaroos with their iconic hopping. 

However, the researchers show that being a kangaroo isn’t strictly about endurance-hopping. In fact, the large-bodied kangaroos from the not-so-distant past were experts at striding and traversing.

Results of the kangaroo hop study were a great surprise

The study undertakes an extensive examination of kangaroo locomotion throughout history, spanning 25 million years. Focusing on kangaroos and their relatives, including wallabies, tree-kangaroos, and rat-kangaroos, it uncovers new insights about their movement. Newly analyzed limb and ankle bone metric data support previous locomotor hypotheses.

These discoveries suggest that high-speed endurance hopping, a hallmark of today’s large-bodied kangaroos, wasn’t a common trait among extinct species. It might have been unique to a few large-bodied lineages, like the direct ancestors of today’s red and grey kangaroos. 

The plethora of kangaroo gaits ceased to exist following the Late Pleistocene extinctions, which wiped out larger animals across various continents.

Extinct kangaroos had different ways of moving around

Yet, the ancient locomotion records speak of a different era. They unveil a period when extinct kangaroos exhibited a broader spectrum of mobility. Early kangaroos, from the late Oligocene to the middle Miocene era (approximately 25 to 15 million years ago), likely used quadrupedal bounding, climbing, and slower hopping.

This contrasts with current kangaroos that resort to quadrupedal movement at slower speeds. The large species also use their tail as a fifth limb in a pentapedal motion. Interestingly, these primitive kangaroo forms were small-bodied, weighing under 12kg. 

Kangaroo hopping is a challenge as body size increases

Kangaroos exceeding 20kg didn’t appear until the late Miocene (around 10 million years ago), correlating with increased aridity and the spread of openly vegetated habitats.

As body size increases, hopping becomes a challenge. Consequently, later kangaroo species developed specialized anatomies that enabled efficient high-speed hopping for bodies over 35kg. No modern kangaroo exceeds 100kg, and many extinct forms were much heavier, making hopping physically impossible.

The lead author of the study, Professor Christine Janis from Bristol’s School of Earth Sciences, stated, “We want people to appreciate that large kangaroos were much more diverse as recently as 50 thousand years ago, which may also mean that the habitat in Australia then was rather different from today. In fact, modern large hopping kangaroos are the exception in kangaroo evolution.”

As kangaroos grew in size during the late Miocene, they explored different movement strategies. While some kangaroos specialized in large-bodied endurance hopping, others experimented with alternative locomotion forms. 

For instance, the protemnodons, dubbed “giant wallabies,” primarily relied on quadrupedal movement, rarely hopping. In contrast, the sthenurine short-faced kangaroos, which split from modern kangaroos around 15 million years ago, embraced bipedal striding.

New data discovered backs up this kangaroo hop theory

The team’s new data on tibia (shin bone) and calcaneum (ankle bone) lengths bolster these locomotor hypotheses. Adrian O’Driscoll, a former Master’s student in the Palaeobiology program at Bristol, and current PhD student at the University of York, supported these findings. 

“Especially supported by this new data is the notion of bipedal striding rather than hopping in the sthenurines. Their calcanea lack the anatomy – a long calcaneal heel – that would help resist rotational forces at the ankle experienced during hopping, suggesting a more-erect limb posture instead of the crouched posture essential for hopping,” said O’Driscoll.

“The assumption that increasing continent-wide aridity after the end of the Miocene selectively favored hopping kangaroos is overly simplistic,” explained Professor Janis. “Hopping is only one of many gait modes employed by kangaroos both in the past and today, and the fast endurance hopping of modern kangaroos should not be regarded as some ‘evolutionary pinnacle’.”

“What makes modern endurance-hopping kangaroos appear so unusual is the geologically recent extinction of similar animals who moved in different ways. We are perhaps then in need of a rival Australian airline that covers shorter distances than QANTAS and boasts a novel motif of a striding sthenurine!”

This breakthrough study underscores the vast diversity of kangaroo locomotion over millions of years. It highlights the richness of kangaroo evolution, which extends beyond hopping. Notably, the research provides a fresh perspective on the remarkable adaptability of kangaroos in response to changing environmental conditions. As such, it rewrites a significant part of Australia’s fascinating prehistoric narrative.

More about kangaroos

Kangaroos are marsupials from the family Macropodidae, a group that also includes wallabies and pademelons. They are native to Australia and are recognized globally for their unique mode of locomotion: hopping. Here are some key points about kangaroos:

Species and distribution

There are four main species of kangaroo: the Red Kangaroo, Eastern Grey Kangaroo, Western Grey Kangaroo, and Antilopine Kangaroo. All are endemic to Australia and each species has its preferred habitat, ranging from forests and woodland areas to savannas and desert-like plains.

Physical characteristics 

Kangaroos are large marsupials, with the Red Kangaroo being the largest, capable of standing over 6 feet tall. They have powerful hind legs designed for hopping and long, muscular tails for balance. Their short forelimbs, equipped with sharp claws, are used for foraging and grooming.

Locomotion and the kangaroo hop

Kangaroos are famous for their hopping, which is an efficient way of travelling great distances in search of food and water. The hopping motion is powered by their strong hind legs and supported by their tail, which acts as a counterbalance. At slow speeds, they use a unique form of locomotion called “pentapedal locomotion,” where they push forward on their tail and forelimbs while bringing their hind legs forward.

Reproduction and life cycle 

Kangaroos are marsupials, meaning they give birth to underdeveloped young, called joeys, which continue developing outside the womb, usually in the mother’s pouch. A newborn joey is tiny, about 1 inch long, and crawls into the pouch to latch onto a teat for nourishment. It will remain in the pouch for about nine months (red kangaroo) before starting to venture out for short periods.

Diet 

Kangaroos are herbivores, eating a variety of vegetation, with a preference for grasses. They have a chambered stomach, similar to cattle and sheep, where bacteria break down the cellulose in the plant matter they eat.

Behavior and social structure 

Kangaroos are social animals, typically found in groups called “mobs,” “troops,” or “courts.” These are usually made up of 10 or more individuals, including males, females, and joeys. Males, known as boomers, will often fight with each other over potential mates by boxing with their forepaws or kicking with their hind legs.

Cultural significance

The kangaroo is a symbol of Australia and appears on the country’s coat of arms, currency, and is used by some of its major organizations, including the national airline, Qantas.

Research continues into the life and history of kangaroos, as highlighted by your earlier enquiry about kangaroo locomotion through history. While this is a general overview of kangaroos, there is a lot more detail to each of these points.

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