A 500kg 'short-faced kangaroo' that walked instead of hopped. Its skull shows it ate tough branches using a single massive lower tooth.
Jonathan Chen, CC BY-SA 4.0, via Wikimedia Commons
The Face of a Giant
During the Pleistocene epoch, the landscapes of South Australia were home to Simosthenurus, the "short-faced kangaroo." This extinct genus belongs to a group known as sthenurines. Unlike modern kangaroos, Simosthenurus had a short, deep skull that more closely resembled a koala's. This unique head shape supported an immensely powerful jaw. Finite element analysis of the skull of one species, Simosthenurus occidentalis, shows it was structurally reinforced with bone, allowing it to produce and withstand very high bite forces.
The animal's powerful jaws were necessary for its diet as a browser, consuming tough, fibrous vegetation like leaves, bark, and branches. Its molars were positioned far back near the jaw's hinge, increasing the mechanical advantage for a crushing bite. Greatly expanded zygomatic arches (cheekbones) anchored large muscles that helped prevent jaw dislocation while chewing resistant food. This anatomy, specialized for crushing hard materials, has been compared to that of the giant panda. Species like S. occidentalis could weigh around 118 kilograms (260 pounds), making them more robust than any living kangaroo.
A Walker, Not a Hopper
The skeleton of Simosthenurus reveals a creature that moved very differently from its modern relatives. Instead of hopping, evidence suggests it walked bipedally, striding on two legs in a manner similar to a person. The anatomical evidence for this is found in its bone structure. Simosthenurus had a broad, flared pelvis and proportionally large hip and knee joints. This structure would have supported large gluteal muscles, allowing it to balance its weight over a single leg at a time while striding.
Evidence also comes from its feet and spine. The hind feet featured a single, large toe ending in a small, hoof-like nail, better suited for walking over flat terrain than for hopping. Its spine was likely more rigid than that of hopping kangaroos, making the bounding motion of modern roos impossible. These kangaroos existed across southern Australia, with fossils frequently found in locations like the Naracoorte Caves, until their extinction around 42,000 to 46,000 years ago. This disappearance was part of a major extinction event that saw the loss of up to 85% of Australia's large-bodied animals.
💡Fun Facts
The skull of *Simosthenurus occidentalis* was biomechanically more similar to a koala's or a giant panda's than to a modern kangaroo's.
Its closest living relative may be the banded hare-wallaby, which is now restricted to a few small islands off the coast of Western Australia.
Fossils of *Simosthenurus* are a significant feature of the Naracoorte Caves, a UNESCO World Heritage site in South Australia famous for its incredibly dense Pleistocene fossil record.
Unlike modern kangaroos that move slowly on five limbs (a "pentapedal" walk using their tail and forelimbs), *Simosthenurus* lacked the flexible spine and tail structure for this kind of movement.
The Naracoorte Caves National Park, a primary fossil site, is open daily. Victoria Fossil Cave tours run at 10:00 am, 12:00 pm, and 2:30 pm. Check the official website for seasonal changes.
Admission
Tour prices for the Victoria Fossil Cave are approximately AUD 35 for adults, with concessions available.
Accessibility
The terrain around the visitor center is accessible. Cave tours involve stairs and walking on uneven ground. Some caves offer accessible platforms.
