August Speaker Report: Pleistocene Megafauna of the Darling Downs

Ian and Diane Sobbe from Clifton brought part of their interesting collection of fossils to this presentation. Ian is a retired farmer, but he has had an interest in fossils since childhood and is now an Honorary Researcher at the Queensland Museum as well as a founder of the Clifton Megafauna Group. The extinct Darling Downs megafauna date from about 85,000 to 120,000 years ago, and their deposition characteristics represent events such as climate change and flood events during this time.

The best known of the megafauna is Diprotodon, a giant herbivorous marsupial standing two metres at the shoulder. Adults had jaws one metre long. Its closest living relatives are probably wombats. Fossil bones of the megafauna are seldom found as complete skeletons. Bones are usually found in deposits resulting from ancient creeks, in meanders where coarser sands and gravels deposited. Skulls tended to wash down first.

Carbon dating has not proved reliable, but an advanced method of dating quartz in which the fossil is deposited has proved more accurate. Quartz begins to absorb radiation when buried, and this can be measured. This dating shows that the megafauna evolved at the time when the climate changed dramatically from about 120,000 years ago. The climate seems to have dried, altering the vegetation from vine thicket to grassland. Remains of frogs and snails in earlier deposits indicate that the environment was much wetter in the past. 

Grassland suited Diprotodon and a whole ecosystem of larger fauna existed, including a five-metre carnivorous reptile Megalania, which was probably related to the extant Komodo Dragon. Three species of crocodile have been identified; one saltwater and one even larger, as well as a terrestrial species. The best-known mammalian carnivore is Thylacoleo, the so-called marsupial lion, a powerful predator with distinctive large premolar teeth and jaws, and musculature for massive bite pressure.

About 30 species of wallabies and kangaroos included some larger than any extant species and including long-faced and short-faced kangaroos. There were also larger wombats standing about one metre high. Speculation

Diprotodon jaw bone

continues as to the reasons for the extinction of Australia's megafauna. Debate concerns climate versus human involvement. Climate change seems to have been the major factor, but research continues.

Remains of megafauna are found over a large part of Australia, but the Downs have revealed a rich share of fossils. Digging and research continues, and new discoveries are being made. Fossil bones are carefully encased and removed for preservation by treatment with a Perspex-like solution. Many megafauna fossils are overseas, in the British Museum and in other places including the Paris Natural History Museum. However, the Clifton group have a large collection, and are hoping to eventually develop a dedicated museum in Clifton. About $5 million is needed to develop the building and interpretative displays.

There are a number of books about the megafauna, and plenty of online information, including short videos of Ian speaking about his work and the museum. Google 'Clifton Megafauna' to view these. There is also a Face-book group; look for Clifton Megafauna Group Inc. If any of you are going to Brisbane, there is a good exhibit of Australia's palaeontology at the Queensland Museum.

Field Naturalist members looking at fossils

(Report by Sheryl Haxen)