Procoptodon
Procoptodon[2] is an extinct genus of giant short-faced (sthenurine) kangaroos that lived in Australia during the Pleistocene Epoch. P. goliah, the largest known kangaroo species that ever existed, stood at about 2 m (6.6 ft).[3] They weighed about 200–240 kg (440–530 lb).[4] Other members of the genus were smaller, however; Procoptodon gilli was the smallest of all of the sthenurine kangaroos, standing approximately 1 m (3 ft 3 in) tall.
Procoptodon physiology was likely similar to that of the contemporary kangaroos; however, Procoptodon goliah was characterised by its large size. These sthenurines, or short-faced kangaroos, included species that were more than three times the size of the largest kangaroos living today. The largest, P. goliah, was 2.7 m (8 ft 10 in) tall and weighed up to 240 kg (530 lb).[5] These animals lived alongside modern species of kangaroos, but specialised on a diet of leaves from trees and shrubs. Procoptodon were large and short-faced, distinguishable by their flat faces and forward-pointing eyes. On each foot, they had a single large toe or claw somewhat similar in appearance to a horse's hoof. On these unusual feet, they moved quickly through the open forests and plains, where they sought grass and leaves to eat. Their front paws were equally strange; each front paw had two extra-long fingers with large claws. They may have been used to grab branches, bringing leaves within eating distance.[6][7]
Procoptodon is mainly known for living in semiarid areas of South Australia and New South Wales. These environments were harsh, characterised by vast areas of treeless, wind-blown sand dunes. However, the area around Lake Menindee, in western New South Wales, had a cooler, wetter climate at the time Procoptodon existed. The surrounding area was a mosaic of sclerophyll forest, woodland, savannah, and plains, but sand dunes would have also formed along the edges of the Menindee.[3] Fossilized footprints have also been found on Kangaroo Island.[8]
Procoptodon was not able to hop as a mode of transportation, and would have been unable to accelerate sufficiently due to its weight.[9] Broad hips and ankle joints, adapted to resist torsion or twisting, point to an upright posture where weight is supported by one leg at a time. Its broad hips also allowed for another important modification – large buttocks – a feature shared with other walking species.[5]
However, some ambiguity surrounds the possible locomotion of P. goliah. Some research suggests that this species was perhaps the largest hopping mammal to have ever existed.[4] Research suggests that the most optimal weight for a large hopping marsupial is roughly 50–60 kg. Larger animals, especially the massive P. goliah, would be substantially more at risk of tendon breakage while hopping.[4] If P. goliah were to have travelled by hopping, the highest possible balance between size and speed would have been peaked, because its body would have been the largest possible to be carried by this method of locomotion.[10]
