Kolopsis torus

Introduction

Kolopsis torus was a mid-sized diprotodontoid from the late Miocene of central Australia. Kolopsisprobably traveled in herds, browsing on leaves, stems and other parts of plants in the subtropical open woodlands of what is now the Northern Territory. Kolopsis lived at a time in Australia when diprotodontoids were both more diverse and more numerous than kangaroos.

Identification

Members of the family Diprotodontidae were quadrupedal, herbivorous marsupials with proportionately large heads (but small brains) and stout limbs. There are two subfamilies in Diprotodontidae: Diprotodontinae and Zygomaturinae. Zygomaturines are distinguished from diprotodontines by a complex upper premolar with from three to five cusps.

Kolopsis torus was a smallish zygomaturine, larger than older Oligocene-Miocene species like Silvabestius or Nimbadon but smaller than the Pleistocene Zygomaturus. Kolopsis torus is distinguished from other zygomaturines by the morphology of the third upper premolar: the outline of P3/ is abbreviated and the parastyle is prominent.

Habitat

The Alcoota region was subtropical open woodland during the late Miocene.

Distribution

Kolopsis torus is known only from Alcoota Station, northeast of Alice Springs in the Northern Territory.

Related to: Kolopsis torus may be most closely related to other named species of Kolopsis,including K. yperus (also from the late Miocene of Alcoota), K. rotundus and K. watutense (from the Pliocene of New Guinea), and an unnamed species of Kolopsis from the late Miocene of Victoria. However, recent work suggests that species of 'Kolopsis' may in fact not be closely related ('Kolopsis' rotundus may be more closely related to other zygomaturines, including the Pleistocene Zygomaturus).

Feeding and diet

Kolopsis torus was a generalist browser, feeding on leaves, stems and shoots of forest plants. It was a zygomaturine, all of which were also browsers rather than grazers.

Life history cycle

Diprotodontoids were obligate herbivores, either browsers or grazers. Like all marsupials, they would have begun life as a tiny neonate that completed its growth after birth in its mother's pouch. Living vombatiforms (koalas and wombats) have a backwardly-facing pouch, and it is probable that diprotodontoids had the same.

Kolopsis torus was a mid-sized diprotodontoid. Like many herbivores in this size range, it was probably prey to large carnivores. At Alcoota, these included two large thylacine species (Thylacinus megiriani and T. potens) as well as Wakaleo alcootensis, a marsupial 'lion'.

Fossils description

Kolopsis torus is known from complete skulls and jaws, postcranial material and isolated teeth. Fossil material is held by the Museum and Art Gallery of the Northern Territory, Alice Springs.

Evolutionary relationships

Diprotodontoids first appear in the late Oligocene, about 25 million years ago. These early diprotodontoids were probably descended from late Oligocene to early Miocene wynyardiids (small marsupials with a dentition intermediate between that of possums and diprotodontids) and were about the size of sheep. Diprotodontoids are included in the suborder Vombatiformes, along with wombats and koalas. Diprotodontidae is divided into the subfamilies Diprotodontinae and Zygomaturinae, distinguished from each other primarily on dental grounds.

Kolopsis torus was a zygomaturine, the diprotodontid subfamily that includes several species of small diprotodontids from New Guinea, Alcoota, central Australia and Riversleigh as well as the larger Zygomaturus from the Pleistocene of Australia. Relationships of Kolopsis and other zygomaturines are currently in flux, in part due to the fragmentary nature of some of the material on which some species have been erected. Kolopsis torus is considered by Peter Murray (1990a) to be one of the most advanced of the zygomaturines, along with the Pleistocene Zygomaturus. Early work on the relationships of zygomaturines found Kolopsis to be a possible direct ancestor of Zygomaturus.

The first large-scale phylogenetic analysis of diprotodontoid relationships (Black 2007), however, finds that the genus 'Kolopsis' includes taxa that are unrelated ('K.' rotundus, which may be basal to the Zygomaturus clade), and that the late Miocene Plaisiodon from Alcoota may instead be the sister taxon to a group including the two valid species of Kolopsis (K. torus and K. yperus), Kolopsoides, Hulitherium and Maokopia from the Pleistocene of New Guinea; and Zygomaturus, all of which have a divided parametacone on P3/.

References

• Anderson, C. 1937. Palaeontological notes. No. IV. Fossil marsupials from New Guinea. Records of the Australian Museum 20, 73-78.
• Black, K. and Mackness, B. 1999. Diversity and relationships of diprotodontoid marsupials. Australian Mammalogy 21, 20-21; 34-45.
• Murray, P. F. 1990a. Alkwertatherium webbi, a new zygomaturine genus and species from the late Miocene Alcoota Local Fauna, Northern Territory (Marsupialia: Diprotodontidae). The Beagle, Records of the Northern Territory Museum of Arts and Sciences 3, 195-211.
• Murray, P. F., Megirian, D. and Wells, R. 1993. Kolopsis yperus sp. nov. (Zygomaturinae, Marsupialia) from the Ongeva Local Fauna: new evidence for the age of the Alcoota fossil beds of central Australia. The Beagle. Records of the Northern Territory Museum of Arts and Sciences 10, 155-172.
• Plane, M. D. 1967b. Two new diprotodontoids from the Pliocene Otibanda Formation, New Guinea. Bulletin, Bureau of Mineral Resources, Geology and Geophysics, Australia 86, 1-64.
• Woodburne, M. A., 1967a. Three new diprotodontids from the Tertiary of the Northern Territory, Australia. Bureau of Mineral Resources, Geology and Geophysics Bulletin, No. 85, 53-103.
• Woodburne, M. O. 1967b. The Alcoota Fauna, central Australia. An integrated palaeontological and geological study. Bureau of Mineral Resources, Geology and Geophysics Bulletin, No. 85, 53-103.

Further reading

• Long, J. A. et al. 2002. Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution. Johns Hopkins University Press, Baltimore, 240 pp.