Riversleigh-Where Nimbacinus came from

I thought I'd give a word about the fossil site where the Nimbacinus skeleton I studied was found. The Riversleigh World Heritage Area is in northwest Queensland, in the Gulf Country. Not many Australians know about it, but it is one of the most significant fossil sites in the country. The rocks literally bristle with bones out there and the level of preservation is exceptional, being three dimensional. There is little evidence of distortion. Many small, delicate fossils that often don't preserve, are very abundant, like these bat bones, below. In the centre of the photo, you can see a bat jawbone:

I went to Riversleigh in 2008 and took these photos. The fossils found date from the Oligocene to the present and the processes that preserved those fossils are still continuing today. Riversleigh is a karst system. This is a geological term for caves. Among the oldest rocks in the area are Cambrian (about 500 million year old) limestones that don't appear to have fossils in them. The rainwater, being slightly acidic due to the carbon dioxide in it, which when dissolved in water becomes carbonic acid. This is the same stuff that makes your fizzy drinks fizzy. It is quite good at dissolving calcite into solution, which can be observed if you drop one your baby teeth in a glass of Coke and leave it there for a very long time. It will eventually disappear, not because the tooth fairy got it, but because the calcium in the tooth has gone into the solution. This creates cavities underground where groundwater flows The calcium in the water gets redeposited in other areas, often on other calcite surfaces. This is how all those amazing structures in caves grow and when the calcite gets deposited over bone, it eventually covers it over and preserves in in three dimensional form. Over time the cave may get filled up by this process or the process of dissolving the limestone may cause the roof of the cave to collapse, creating a sinkhole. Animals may fall into these holes where they perish and their bones get preserved this way. This is the likely way that the Nimbacinus skeleton was fossilised. Nimbacinus was recovered from a massive sinkhole. There are many sinkholes and other fossil deposits in Riversleigh, which are all considered different fossil sites and each site has a name. The site where the study skeleton was found was called AL90. but on the tireless quest for fossils using sledge hammers and explosives, Nimbacinus was found. It was isolated in a large rock of its own, from about 30 Nimbadon lavarackorum skeletons of all ages and sizes. It was found curled up like a sleeping dog, like as if it has realised there was no escape from the sinkhole and had given up. Nimbadon were sheep sized wombat-like creatures, one of the now extinct zygomaturine diprotodontids. The site was originally a flat, level surface, but is now a massive hole in the ground, which is affectionately called "The Swimming Pool;" which you can see below:

This photo (above) also illustrates what Riversleigh looks like in present times. When Nimbacinus was alive it was a lush rainforest, remnants of which can be found clinging to the nearby Gregory River:

Nimbacinus dicksoni

Until now, life has moved at such a violent pace that I have not been able to return to this blog until now. I am nearly 26 and my life is completely different to the circumstances I was living in back in 2009. It feels like another world. In April 2008, my Mother died and my immediate family entirely fragmented. Since that point, until quite recently, I was very much alone in my struggles. At the end of 2009, I gradated with a Bachelor of Science with majors in geology and zoology from the University of Tasmania. I then relocated to Sydney to complete my Honour's year in vertebrate palaeontology, which will be the subject of this post. The course is only supposed to take a year, but due to untold dramas including assault and homelessness and the general incompetance of people and the system, I emerged, at the end of 2011, in triumph with a grade of 2nd Class 1st Division and this reconstruction of Nimbacinus dicksoni:

Nimbacinus was a 15 million year old thylacinid, which are a group of carnivorous marsupials that resembled canids because they evolved to follow similar lifestyles, not because they were closely related. They only became extinct fairly recently, in 1936, when the last Tasmanian tiger died in a zoo in Hobart, Tasmania. (I used to drive passed the remains of this zoo every time I went to university in Tasmania.) The Tasmanian tiger, (Thylacinus cynocephalus) was the largest Australian marsupial carnivore and was approximately the size of a German Shepard dog. It was called a tiger because of the dark stripes it bore on its hindquarters. Here is a photo of the late Tasmanian tiger:

The title of my thesis is Postcranial morphology of Nimbacinus dicksoni (Thylacinidae: Marsupialia) and a discussion of the functional morphology of the limbs. That may seem like a daunting mouth full but all it means is that I described all the bones of this animal except for the skull, which was already described by Steve Wroe and Anne Musser in 2001, and I discussed how it may have used its limbs when it was alive. I also did a head reconstruction of Nimbacinus based on figure 3 of Steve Wroe and Anne Musser's cranial description.

A large part of the requirements of the work was that I produce stippled drawings of all the bones of Nimbacinus and of the Tasmanian tiger and described them anatomically in the text. Here is the ventral vew of the pelvis of the Tasmanian tiger:

Overall, I had to produce nearly 60 of these such images, each bone was illustrated in anywhere from three to five different angles to demonstrate their significant features. I did an average of three drawings a day for nearly six months. I concluded that Nimbacinus was not just a miniture Tasmanian tiger. The former was about the size of a fox. Proportionately, Nimbacinus had stronger forelimbs, so whatever it did in terms of hunting, it was consuming different prey than the Tasmanian tiger and possibly doing a lot of grappling with it. The Tasmanian tiger, on the other hand, was more of a pursuit predator that chased small wallabies.