Monday 14 April 2014

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).

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