Procoptodon goliah
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Procoptodon Temporal range: Pleistocene |
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| Procoptodon goliah | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Infraclass: | Marsupialia |
| Order: | Diprotodontia |
| Family: | Macropodidae |
| Subfamily: | Sthenurinae |
| Genus: |
†Procoptodon Owen, 1873 |
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Procoptodon is a genus of giant short-faced kangaroo living in Australia during the epoch. P. goliah, the largest-known kangaroo that ever existed, stood approximately 2 m (6.6 ft). They weighed about 232 kg (511 lb). Other members of the genus are smaller, however, and Procoptodon gilli is the smallest of all of the sthenurine kangaroos, standing ~1m tall.
Procoptodon goliah was 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, 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. Fossilized footprints have been found on Kangaroo Island.
Procoptodon physiology was likely similar to that of the contemporary kangaroo; however, Procoptodon goliah were characterised by their large size. These sthenurines, or short-faced kangaroos, included species that were more than three times the size of the largest kangaroos today. The largest, Procoptodon goliah, was 2.7 metres tall and weighed up to 240 kg. These animals lived alongside modern species of kangaroo, but specialised on a diet of leaves from trees and shrubs. P. goliah were giant, short-faced kangaroos that were 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. It is possible that they were used to grab branches, bringing leaves within eating distance.
Procoptodon goliah were unable to hop as a mode of transportation, and would have been unable to accelerate sufficiently due to their mass. 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, Their broad hips also allowed for another important modification: large buttocks - a feature shared with other walking species. However, there is some ambiguity surrounding the possible locomotion of the P. goliah. Some research suggests that this species was perhaps the largest hopping mammal to have ever existed. Research suggests that the most optimal weight for a large hopping marsupial is approximately 50–60 kg. Larger animals, especially the massive P. goliah, would be substantially more at risk of tendon breakage while hopping. If P. goliah were to have travelled by hopping, the highest possible balance between size and speed would have been peaked because their bodies would surely have been the largest possible to be carried by this method of locomotion A more likely suggestion, based on the apparent anatomy allowed by the bone structure of P. goliah, is that unlike modern kangaroos, which are plantigrade hoppers at high speeds and use their tails in pentapedal locomotion at slower speeds, Procoptodon was an unguligrade biped, walking in a fashion similar to hominids. Locomotion mechanics and physiology have been investigated through the examination of muscleoskeleton scaling patterns. The largest, Procoptodon goliah, was 2.7 metres tall and weighed up to 240 kg. For Procoptodon goliah, tendon stress was identified, which indicates limited locomotor capabilities, exposing a correlation between body mass and locomotion abilities. Ruptures in tendons demonstrate strain in elasticity of muscles in the limbs which provides evidence that perhaps the hypothesised ability for the Procoptodon goliah to hop may have been unlikely. Due to their locomotive performance, the species may have been vulnerable to human predation. Fossils of giant short-faced kangaroos have been found at the Naracoorte World Heritage fossil deposits in South Australia, Lake Menindee in New South Wales, Darling Downs in Queensland, and at many other sites. A full-size, lifelike replica is on permanent display with other ancient native Australian animals at the Australian Museum.
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