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Modern large hopping kangaroos are uncommon in kangaroo evolution
50,000 years ago, diverse types of large kangaroos existed, indicating changes in the Australian habitat
Kangaroos are unique among large mammals as they primarily move by hopping on two legs
The famous kangaroo in Australia jumps with its strong back legs in the outback or in front of cars during the evening. However, according to scientists, extinct large kangaroos probably moved in different ways, such as walking on two legs or using all fours.
Scientists from the Universities of Bristol and York in the UK, and Uppsala University in Sweden, studied old bones and analyzed data from the shin and ankle bones of kangaroos, wallabies, and their relatives. They wanted to understand how these animals moved over the last 25 million years.
The team's review reveals that the famous hopping style of kangaroos, like the Qantas Airlines logo, is just one way they move and not the ultimate form of their evolution. According to Christine Janis, a scientist from the University of Bristol, modern large hopping kangaroos are actually rare in the history of kangaroo evolution. Around 50,000 years ago, there were more diverse types of large kangaroos, suggesting that the Australian habitat was different back then.
Kangaroos are unique among large mammals as they primarily move by hopping on two legs, which fascinates scientists. However, previous research has mainly focused on larger kangaroos, leaving a gap in our knowledge about their smaller counterparts.
By studying the fossil record, researchers analyzed the shin bones and heel bones of kangaroos and their marsupial relatives. They discovered that the ability to hop at high speeds, a characteristic of modern large-bodied kangaroos, was rare in most lineages. However, direct ancestors of red and gray kangaroos possessed this trait. About 25-50 million years ago, smaller macropodoids were agile and could bound, climb, and hop. As the climate became drier and habitats more open around 10 million years ago, larger macropodoids emerged.
Modern kangaroos, like the red kangaroo and male eastern gray kangaroo, have reached an ideal weight for efficient hopping. However, extinct kangaroos were often larger than them, and interestingly, hopping becomes more difficult as the size increases.
In the past, larger kangaroos had two options: either develop specialized anatomy, such as long slender heel bones for faster hopping or utilize alternative locomotion methods to traverse terrain at higher speeds. This was observed in two extinct lineages.
The extinct 'short-faced kangaroo' known as sthenurine adopted bipedal 'striding' for movement at all speeds. However, they lacked the heel capacity for hopping due to their large size. The largest of them, Procoptodon goliah, weighed over 200 kilograms.
The protemnodons, closely related to modern large kangaroos, had short and broad feet, similar to tree kangaroos, which were not well-suited for hopping. They likely predominantly walked on all fours.
The broad heel bones of these extinct groups suggest they stood more upright compared to today's crouched kangaroos. The recent extinction of similar animals that moved differently makes modern endurance-hopping kangaroos appear unusual.
Currently, all kangaroos use quadrupedal locomotion for slow travel, with larger species utilizing their tail as a fifth limb (pentapedal). The diversity of kangaroo gaits decreased with the extinction of larger animals during the Late Pleistocene.
The assumption that increasing aridity favored hopping kangaroos is overly simplistic. Kangaroos employ various gait modes, and the fast endurance hopping of modern kangaroos should not be considered the sole 'evolutionary pinnacle'.
The review has been published in Alcheringa: An Australasian Journal of Palaeontology.
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