Reconstructing the diet of a Miocene Thylacinid.

Thylacinids (Thylacinidae) were large carnivorous Australian Marsupials that appeared in the Late Oligocene and survived until the 1930s. Twelve species have been described, largely from fragmentary material, ranging in size from about 1 kg to about 60 kg. Most reconstructions of the lifestyle of fossil Thylacinids have been based upon the historic Thylacine or Tasmanian Tiger (Thylacinus cynocephalus), a Dog-like carnivore driven to extinction by human activity in the early twentieth century, but the wide range of sizes found within the group suggests that this may not be a good model for every species.

In a paper published in the journal PLoS One on 9 April 2014, a group of scientists led by Marie Attard  of the Evolution and Ecology Research Centre at the School of Biological, Earth and Environmental Sciences at the University of New South Wales and Function, Evolution and Anatomy Research laboratory at the School of Environmental and Rural Sciences at the University of New England, digitally reconstruct the skull of a middle Miocene Thylacinid, Nimbacinus dicksoni, in order to try to determine its diet and lifestyle.

The skull of Nimbacinus dicksoni was collected from the Gag Plateau of the Riversleigh World Heritage Site in northwestern Queensland, and currently resides in the Queensland Museum in Brisbane. It is largely complete, but some bones are missing or damaged. It is thought that the living animal would have weighed about 5 kg, making it considerably smaller than the Thylacine, but within the size range of modern Quolls, smaller Marsupial carnivores related to the Thylacinids and still found across much of Australia.

Attard et al. constructed a three dimensional digital model of the skull of Nimbacinus dicksoni, and used it to model the mechanical behavior of the skull during feeding. This model of the skull and its biomechanical properties was compared to similar models of four modern Marsupial carnivores, the Thylacine (Thylacinus cynocephalus), the Tasmanian Devil (Sarcophilus harrisii) and the Spotted-tailed and Northern Quolls (Dasyurus maculatus and Dasyurus hallucatus).

Digital reconstruction of Nimbacinus dicksoni. Original (grey) and reconstructed 3D (yellow) in (A) lateral view and (B) dorsal view. (C) Pre-processed Finite Element model of N. dicksoni, showing jaw musculature represented by trusses. Attard et al. (2014).

The stress tolerances of the skull of Nimbacinus dicksoni were closest to those of the Tasmanian Devil (Sarcophilus harrisii) and the Spotted-tailed Quoll (Dasyurus maculatus), both opportunistic hunters willing to tackle large prey should it become available. This suggests that Nimbacinus dicksoni may have had a similar lifestyle to these smaller, but more ferocious predators, tackling large prey compared to its own size, a behaviour that would not be inferred by comparison with Thylacinus cynocephalus.

Von Mises stress under a bilateral canine bite in lateral view. The models are subjected to a load applied to both canines, with bite force scaled based on theoretical body mass. Species modeled were (A) Dasyurus hallucatus, (B) Dasyurus maculatus, (C) Sarcophilus harrisii, (D) Nimbacinus dicksoni and (E) Thylacinus cynocephalus. White colored regions of the skull represent VM stress above 10 MPa. Attard et al. (2014).

See also...

 A 'South American' Marsupial from the early Eocene of Australia.

 What killed the Australian Thylacine?

 Walking with Giant Wombats.

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What killed the Australian Thylacine.

The Thylacine, also known as the Tasmanian Tiger or Marsupial Wolf, was a large, predatory, marsupial mammal which roamed Australia from about four million years ago until about 3500 years ago, when it became extinct on the Australia mainland, though it persisted on the island of Tasmania till the twentieth century. The period when the Thylacine went extinct on the Australian mainland co-insides with the adoption of a number of new technologies by human populations across mainland Australia (but not Tasmania) leading to a rise in human populations across the continent, and also the introduction of Dingos (wild dogs) to mainland Australia (but again, not Tasmania). These two events are both likely to have contributed to the downfall of the mainland Thylacines, though the contribution of each to the eventual extinction has been hard to assess.

A Thylacine, front, and a Dingo, behind. Carl Buell.

Invasive predators can cause problems for their indigenous rivals in a number of ways. Most obviously they often tend to outcompete them. Prey animals that evolved alongside the indigenous predator will have developed methods of avoiding predation by it, but are often unable to cope with the invasive predator, which may use novel, unfamiliar hunting strategies (such as hunting in packs, which Dingos do, but which Thylacines are not thought to have done). This will cause the incoming predator to suppress prey numbers till they have time to adapt to the novel predation methods. This is more damaging still if individual members of the new species have a larger individual prey requirement; again this is likely to have been the case with the placental Dingos being presumed to have had a faster metabolism than the marsupial Thylacines.

Introduced predators can be even more of a threat if they directly attack members of the indigenous species. Predators will often attack and kill members of smaller predatory species with which they compete, even if they do not actually eat the rival species. Like prey items, predators may be particularly vulnerable if they encounter a novel rival species which behaves in ways they have not evolved to counter.

Until now Thylacines have been thought to have been reasonably safe against direct attacks by Dingos, as members of the surviving twentieth century population in Tasmania were too large, with the females matching the largest Dingos in size, and the males being considerably larger.

In a paper published in the journal PLoS One on 2 May 2012, Mike Letnic of the School of Biological, Earth and Environmental Sciences at the University of New South Wales, Melanie Fillios of the Department of Archaeology at the University of Sydney and Mathew Crowther of the School of Biological Sciences at the University of Sydney, discuss the results of a study of subfossil Dingo and Thylacine specimens from the Western Australian Museum, gathered in temperate southwest Australia and the semi-arid Nullarbor region.

This revealed that he Thylacines of southwest Australia and the Nullarbor region were considerably smaller than those of Tasmania, with only the largest males being comparable in size to a Dingo, and the females typically being around half the size. This suggests that any hostile encounters between the solitary Thylacines and the pack-hunting Dingos would have gone very badly for the Thylacines. Even if the Dingos only targeted female Thylacines the effect on the Thylacine population level would have been devastating; most animals can cope with a sharp drop in the number of male animals, but females are essential to maintaining the population.

Skulls from the Western Australian Museum. Left, female Thylacine. Center, male Thylacine. Right, Dingo. All from the Nullarbor region. Scale bar is 5 cm. Letnic, Fillios & Crowther (2012).

Sufficient material was not available from other regions to assess the sizes of Thylacines across continental Australia, but individual teeth from southeast Australia and a partial skull from the Cape Range in the northwest of the continent suggest that the samples from the Western Australian Museum are a better model than those from Tasmania.

See also New species of Velvetfish from the Kimberly Coast of Western Australia, A new Bent-toed Gecko from Western Australia, Possible impact crater in Palm Valley, Northern Territory, Australia, Fishermen targeting tuna in East Timor at least 42 000 years ago, Walking with Giant Wombats and Mammals on Sciency Thoughts YouTube.

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