Specimen of the Week 223: The Tasmanian wolf
By Paolo W Viscardi, on 18 January 2016
One of the most interesting things about zoology for me is the way in which skulls are sculpted by evolutionary and environmental forces. A particularly fascinating outcome of such processes is convergent evolution, which occurs when distantly related organisms live in a similar environment and have a similar mode of life, resulting in them looking and often behaving like each other. My favourite example of this phenomenon is shown by my Specimen of the Week…
**the Tasmanian wolf (Thylacinus cynocephalus)**
Gone but not forgotten
The thylacine went extinct in 1936, with the last individual expiring as a captive at Hobart Zoo in Tasmania. Thanks to their taste for chickens and (purportedly) sheep, the species was relentlessly persecuted by farmers from the 1830s, with a bounty offered by the Tasmanian government during the latter part of the 19th century. Disease, competition from feral dogs, extinction of prey species and men with guns put a lead nail in the thylacine’s coffin.Despite this depressing tale, we do at least have quite a few specimens in museums around the world, which can tell us something about this extinct, but iconic species.
The common name of the thylacine is a bit misleading, since the species had been quite widespread across Australia and even New Guinea until around 2,000 years ago, when they were ousted by competition from dingoes and wild dogs. Tasmania did however remain a safe haven for the thylacine until it became settled by Europeans in 1803, who brought their dogs and guns.
Another misleading element of the thylacine’s common name is the ‘wolf’ bit. Despite eating meat the thylacine was not a true Carnivore (note the capital ‘c’) like wolves and dogs. In fact, the decidedly doggy appearance is very misleading, since man’s best friend shares more common ancestry with a blue whale than with a thylacine. The Tasmanian wolf was actually a marsupial and more closely related to a kangaroo or possum, with pouch and all. In fact, even the males had a pouch (which is very unusual), providing a mechanism for protecting their delicate parts when running through snaggy undergrowth. After all, who wouldn’t want to avoid snagging a testicle on something sharp when moving at speed?
Similarities and differences
Considering the lack of a close relationship between thylacines and dogs, the similarity between their skulls is quite remarkable:
As you can see, the overall shape is broadly the same – in fact the shape difference can be far more extreme between two different breeds within the domestic dog species.When it comes to evolutionary convergence the similarities we see tend to be functional, so you expect to see certain shared features of the skull and teeth for medium to large carnivores (small ‘c’) that hunt small to medium sized prey by chomping on them or ripping bits off. However, when you look at the finer details of convergent species you tend to see differences occurring that are due to relationships rather than function.
A good example of this can be seen in the bony palate of the thylacine compared to the dog. Marsupials have an incompletely ossified palate, whereas placental mammals have a solid bony roof to their mouth. Marsupials also have their tear duct on the outside border of the eye socket, whereas placentals have it on the internal border. It’s these little features that make it easy to spot the difference between a thylacine and a dog skull – at least for those who know what to look for.
Finally, this Specimen of the Week caught my eye more than the other Tasmanian wolf skulls in the collection because it’s by far the biggest I’ve ever seen, measuring in at 256mm (measured from prosthion to inion using calipers). This is in the same size range as a female northern timber wolf and presumably reflects that the animal it came from was a really big male thylacine. It would be great to know if anyone has seen a bigger example!
Paolo Viscardi is the Curator of the Grant Museum of Zoology