Palorchestes ("ancient leaper") is an extinct genus of large terrestrial, herbivorous Australian marsupial of the family Palorchestidae, living from the Miocene through to the Late Pleistocene. Like other palorchestids, it had highly retracted nasal region suggesting that it had a prehensile lip, as well as highly unusual clawed forelimbs that were used to grasp vegetation.
Taxonomy
The generic name was coined in 1873 by anatomist Richard Owen, who first found what he thought was the fragmentary jaw of a prehistoric kangaroo and derived the name from ancient Greek terms for "ancient" and "leaper". Despite Owen explicitly stating the etymology of the name in his description, palaeontologist Harold Fletcher published a translation as "the ancient dancer" in 1945. When more postcranial elements were found, Palorchestes was realized as not a macropod, but a diprotodontid. Owen's description as a giant kangaroo was revised in 1958 by Jack T. Woods of the Queensland Museum, allying the genus to the Diprotodontia order.
Another genus is probably ancestral to these species, thus named Propalorchestes; it shared some characteristics of the molars, but had shorter jaws and therefore snout.
The genus is represented in the fossil record by five or six species, Palorchestes P. anulus Black 1997 P. azael Owen P. painei Woodburne, 1967 P. parvus De Vis, 1895 P. pickeringi P. selestiae Mackness, 1995
The fossil dentary of a young adult found in Pleistocene deposits in the Darling Downs region of southeast Queensland, although limited by the rarity of specimens and comparable remains of the genus, was distinguishable from P. azael, P. parvus, and P. painei. The specimen provides evidence of sympatry with another species of the genus, rather than the apparent sequence of form and size from the mid-Miocene to recent era, and may represent a new species or sexual dimorphism in a smaller species.
The genus was allied to other diprotodontid genera, Ngapakaldia and Pitikantia, firstly recognised as a subfamily Palorchestinae (Stirton, 1967), later elevated to familial status with the order (Archer and Bartholomai, 1978).
Description
Palorchestes azael, was similar in size to a horse, being around in length, with quantitative body mass estimates based on humerus and femur bones indicating its body mass could well have exceeded . Palorchestes species had four powerful legs, with the front legs bearing large claws, similar to those of a koala, which they probably used to pull down leaves and strip the bark from trees. The long symphysis at the lower jaw of all Palorchestes species indicates that their tongues were long and protrusible, like that of a giraffe. The appearance of the animals' nasal bones suggests that they possessed a short proboscis, leading to the nickname of the "marsupial tapir". However, a recent study that reviewed the cranial morphology of various Palorchestes species and the related genus of Propalorchestes showed strong support for well-developed prehensile lips, rather than a tapir-like proboscis.
A structural detail of the first molar is regarded as characteristic of this genus, the development of a midlink at the crown, distinguishing it from the earlier Propalorchestes and other Miocene genera. The dentition and morphological features of the genus indicate they browsed for plant material such as shrubs and roots.
Distribution and habitat
Specimens of Palorchestes have been found at sites in the east of the Australian continent (Sahul at the time). The locations of specimens diagnosed as the species number over 30 sites, dated as Pliocene and Pleistocene, and most well represented by the later species P. azael. Remains of P. azael have been found at the Naracoorte Caves fossil site in Australia. The genus is represented in the biostratigraphy of the Riversleigh mammal sites, becoming abundant in the more recently dated deposits, which along with other diprotodontoid taxa provides evidence that may be correlated to similar analysis of other sites in Australia and elsewhere.
Paleobiology
The morphology of the skull, teeth, and dental microwear analysis suggest that Palorchestes was a selective browser. The unusual morphology of palorchestids makes their ecology difficult to interpret. The elbow of Palorchestes had an unusually limited range of motion, which means that the forelimbs would have sprawled when the animal was walking quadrupedally. Palorchestes likely used its forelimbs to attain foliage, and may have fed in a bipedal posture. Due to the extreme rarity of its remains, some authors have interpreted it as a solitary animal that had large ranges and slow reproductive rates.