Powerful Thylacine

Introduction

Thylacines were dog-like marsupial carnivores whose last representative, the Tasmanian 'Tiger', tragically became extinct last century. The late Miocene Thylacinus potens, known only from a single upper jaw, was one the largest of the thylacines. Only Thylacinus megiriani, from the same deposit as T. potens (Alcoota in the Northern Territory), was larger.

Identification

Thylacines were quadrupedal marsupial predators. The last of the thylacines were remarkably dog-like, with long snouts and molar teeth specialized for carnivory (the cusps and crests reduced and/or elongated to form cutting blades on the molars). Over ten thylacine species are now known from northern and central Australia. They ranged in size from those the size a quoll ('native cat') to species of Thylacinus that were larger than the recently extinct Tasmanian 'Tiger', Thylacinus cynocephalus. Thylacines were generally quite similar to one another, differing mainly in their dentitions. These dental differences may reflect differences in diet, although all were at least to some extent carnivorous.

Thylacinus potens differs from T. cynocephalus in its larger size and in features of the palate and molar teeth. It would have weighed about 38-39 kilograms, heavier than T. cynocephalus (estimated weight: 29.5 kilograms) but much smaller than T. megiriani(estimated weight: over 57 kilograms). These body weight estimates are larger than the average weight calculated for living canids: dogs, wolves and their relatives. Even allowing for possible factors that could skew the weight ratio, such as proportionately large teeth in T. megiriani and T. potens, these were large and formidable animals.

Habitat

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

Distribution

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

Feeding and diet

The following information on the diet of the Tasmanian Thylacine, Thylacinus cynocephalus, probably applied to Thylacinus potens. The main difference may have been that T. potens, being slightly larger, could have taken larger prey.

T. cynocephalus subsisted mainly on a diet of wallabies, but was known to take other small mammals and birds (and occasionally sheep or chickens). A comparative study of bite force in mammalian predators found that biomechanically the Tasmanian thylacine could take relatively large prey, although there is no first-hand evidence for this. It scavenged on occasion, and thylacines held in captivity devoured dead rabbits, wallabies, sheep and beef.

Life history cycle

The following account is of the life history of T. cynocephalus, much of which would have applied to T. potens.

Thylacines bred during winter and spring, and the young were born tiny and hairless, as in all marsupials. The pouch faced to the rear, an advantage for an animal that ran down its dinner. Female thylacines had four teats and could carry as many young, although three young per litter was probably the norm. After leaving the pouch, young remained in a protected nest, hollow log or cave while the female hunted. Thyacines were unable to be bred in captivity. One captive animal survived to the age of nine, although thylacines would have lived from five to seven years in the wild.

Fossils description

Thylacinus potens is known only from a partial palate, held by the Museum and Art Gallery of the Northern Territory, Alice Springs.

Evolutionary relationships

The discoveries of so many new thylacine species over the past two decades re-ignite the debate over thylacine relationships and over who their immediate ancestors were. The traditional view has been that thylacines were descended from a dasyurid ancestor perhaps during the Oligocene. The first phylogenetic analysis incorporating data from Nimbacinus dicksoni found an alternative result, that thylacinids were actually the older and more 'primitive' group and that dasyurids were a newer and more specialized group (Wroe and Musser 2001). The results of a subsequent analysis of thylacine relationships (in a paper describing another Miocene thylacine, Mutpuracinus) retrieved the traditional arrangement, with thylacines above dasyurids in the dasyuromorphian tree (Murray and Megirian 2006). No further studies based on firsthand investigation of fossil thylacines have been published. The question of thylacinid relationships must therefore be considered unresolved.

References

• Archer, M. 1982. A review of Miocene thylacinids (Thylacinidae, Marsupialia) the phylogenetic position of the Thylacinidae and the problem of apriorisms in character analysis. Chapter 38 in Archer, M. (ed) Carnivorous Marsupials, Vol. 2.Royal Zoological Society of New South Wales, Mosman.
• Muirhead, J. 1992. A specialized thylacinid, Thylacinus macknessi (Marsupialia: Thylacinidae) from Miocene deposits of Riversleigh, northwestern Queensland. Australian Mammalogy 15, 67-76.
• Murray. P. F. 1997. Thylacinus megiriani, a new species of thylacine (Marsupialia: Thylacinidae) from the Ongeva Local Fauna of central Australia. Records of the South Australian Museum 30, 612-626.
• Wroe, S. 2001. Maximucinis muirheadi, gen. et sp. nov (Thylacinidae: Marsupialia), from the Miocene of Riversleigh, north-western Queensland, with estimates of body weights for fossil thylacinids. Australian Journal of Zoology 49, 603-614.
• Wroe, S., McHenry, C. and Thompson, J. 2005. Bite Club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa. Proceedings of the Royal Society B doi:10.1098/rspb.2004.2986.
• Woodburne, M. O. 1967. The Alcoota Fauna, central Australia: an integrated palaeontological and geological study. Bureau of Mineral Resources Australian Bulletin 87, 1-187.

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.