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: