According to a comprehensive analysis conducted by scientists from the University of Bristol and the University of Uppsala, extinct kangaroos utilized alternative methods of locomotion beyond their famous hopping. While hopping is considered a significant evolutionary trait of kangaroos, the researchers emphasize that large kangaroos in the relatively recent past likely employed different modes of movement, such as striding on two legs or moving on all fours.
The review, published in Alcheringa: An Australasian Journal of Palaeontology, presents an extensive examination of fossil evidence regarding the locomotion of kangaroos and their relatives over the past 25 million years. The study includes new analyses of limb bone and ankle bone metrics, which support previous hypotheses regarding locomotor diversity.
The findings indicate that the high-speed endurance hopping observed in modern large-bodied kangaroos was likely rare or absent in most large-bodied lineages, with few exceptions like the direct ancestors of present-day large kangaroos such as red and gray kangaroos. However, the variety of kangaroo gaits diminished with the extinction of larger animals during the Late Pleistocene, both in Australia and other continents.
While hopping is employed to some extent by almost all kangaroos today, the fossil record reveals that extinct kangaroos had comparatively diverse locomotory capabilities.
Early kangaroo species from the late Oligocene to middle Miocene period (25 to 15 million years ago) likely utilized quadrupedal bounding, climbing, and slower speed hopping as their primary modes of locomotion. Present-day kangaroos utilize quadrupedal locomotion at slow speeds, which is manifested as pentapedal locomotion in larger species, utilizing the tail as a fifth limb. However, these early kangaroo forms were small-bodied, weighing less than 12 kg, and larger-bodied kangaroos weighing over 20 kg only appeared in the late Miocene (around 10 million years ago) when aridity increased, and open vegetated habitats spread.
Hopping becomes functionally problematic as body size increases. As a result, some members of later kangaroo lineages evolved specialized anatomical features for efficient high-speed hopping at body sizes over 35 kg. Modern large kangaroos are impressive hoppers, but none today exceed 100 kg (with most individuals under 70 kg), and many extinct species were even larger and physically unable to hop.
Professor Christine Janis, the lead author from Bristol’s School of Earth Sciences, stated, “We want people to appreciate that large kangaroos were much more diverse as recently as 50,000 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.”
While hopping likely originated early in kangaroo evolution among small-bodied species, the emergence of larger-sized kangaroos in the late Miocene presented several options: specializing in large-bodied endurance hopping, as seen in the ancestors of modern kangaroos, or adopting other forms of locomotion at higher speeds, as observed in two main extinct lineages. The protemnodons, known as “giant wallabies” and closely related to modern large kangaroos, likely primarily employed a quadrupedal form of locomotion and rarely hopped. On the other hand, the sthenurine short-faced kangaroos, a lineage that diverged from all modern kangaroos around 15 million years ago, apparently adopted bipedal striding at all speeds.
The newly presented data on tibia (shin bone) and calcaneum (ankle bone) length support these earlier hypotheses of locomotor differences between modern kangaroos and these two extinct groups. Co-author Adrian O’Driscoll, a former Master In conclusion, the assumption that increasing aridity favored hopping kangaroos after the Miocene period is oversimplified. Hopping is just one of many locomotion modes utilized by kangaroos both in the past and present. The remarkable endurance hopping seen in modern kangaroos should not be seen as the ultimate evolutionary achievement.
The study suggests that the uniqueness of modern kangaroos lies in the recent extinction of similar animals that moved in different ways. The researchers even humorously propose the idea of an Australian airline with a different motif—a striding sthenurine kangaroo—as a rival to QANTAS.
Source: University of Bristol