Skipping Evolution: Some Kangaroos Didn't Hop
Published:14 Jul.2023 Source:University of Bristol
Although hopping is regarded as a pinnacle of kangaroo evolution, the researchers highlight that other kinds of large kangaroos, in the not too distant past, likely moved in different ways such as striding on two legs or traversing on all fours. While almost all kangaroos today, small and large, use hopping gaits to some extent, the fossil record reveals that the locomotory capabilities of some extinct kangaroos were comparatively diverse.
The earliest recognized late Oligocene-middle Miocene (25to 15 million years ago) basal types of kangaroos most likely employed quadrupedal bounding, climbing and slower speed hopping as their primary modes of locomotion. (All kangaroos today use quadrupedal locomotion at slow speeds, which manifests as pentapedal locomotion -- using the tail as a fifth limb -- in larger species.) Yet, all these early forms were small-bodied, below 12kg, with larger bodied kangaroos over 20kg not appearing until the late Miocene (around 10 million years ago), coinciding with increasing aridity and the spread of openly vegetated habitats.
While hopping apparently originated early in kangaroo evolution, in small-bodied forms, with the emergence of larger-sized kangaroos in the late Miocene there were several different options: to become more specialized for large-bodied endurance hopping, as in the ancestors of modern kangaroos, or to adopt other forms of locomotion at higher speeds, as in two main extinct lineages. The protemnodons (so-called 'giant wallabies', closely related to modern large kangaroos) likely relied upon a more quadrupedal type of locomotion most of the time, and rarely hopped. The sthenurine short-faced kangaroos, a lineage that split from all modern kangaroos around 15 million years ago, apparently adopted bipedal striding at all speeds.