Wednesday 6 July 2011

Walking with Giant Wombats.

This week scientists in Australia unveiled a new specimen of Diprotodon optatum, an extinct rhinoceros sized marsupial widely referred to in the press as a 'Giant Wombat'. Diprotodon is a fairly well documented animal, but this specimen is one of the most complete and well preserved found to date, as well as being the most northerly specimen yet discovered.
A specimen of Diprotodon from Natural History Museum in London.

The specimen was uncovered at Floraville Station by the Liechardt River in the Gulf of Carpentaria, between the towns of Burketown and Normanton. The dig was lead by Mike Archer and Henk Godthelp of the University of New South Wales, Scott Hucknell of the Queensland Museum and Gilbert Price of the University of Queensland. The excavation formed part of a wider Australian Research Council Linkage Project into climate change in Northern Australia, led by Sue Hand, also of the University of New South Wales, and including scientists from the Australian Nuclear Science and Technology Organisation, the University of Melborne, the University of Wollongong, and Outback at Isa.

Diprotodon was found across Australia from about 2.5 million years ago, until sometime after 55 000 years ago, the date of the most youngest specimen yet dated (bone tissue from the Floraville Station specimen has been taken for dating, but no results are yet in). It is suspected that Diprotodon died out, along with other members of the Australian megafauna, at roughly the time the first humans arrived in Australia. The earliest known human remains in Australia are a pair of skeletons from Lake Mungo in New South Wales, imaginatively dubbed 'Mungo Man' and 'Mungo Woman', dated at 40 000. Humans had clearly lived in Australia some time before this, as Lake Mungo is not near any probable site for the first arrivals.

The excavation of Mungo Man.

Australia underwent a change in climate at roughly the same time that the first humans settled the continent. Palaeoclimatologists argue as to whether this climate change was due to natural causes, or human activity, in particular the practice of burning vegetation. In addition archaeologists argue as to whether this climate change was the cause of the loss of the Australian megafauna, or whether humans were more directly involved in the extinctions, hunting animals to extinctions. The same debate occurs on other continents, particularly North America, where human arrival coincided with megafauna extinctions.

The dating of the Floraville Station Diprotodon, and other megafauna components from the same site, such as giant kangaroos and lizards, combined with studies of the climatic conditions at the site, could potentially shed light on this debate.

The scientists also hope to see how the skeleton differed from animals from further south. There were once eight named species of Diprotodon across Australia, but a review of the specimens by Gilbert Price, one of the scientists on the Floraville Station dig, suggested that there were only actually two different body plans, and that most large Australian marsupials showed a strong degree of sexual dimorphism, which lead him to the conclusion that there was only a single species, Diprotodon optatum, the original species described in 1838 by the British zoologist Richard Owen. Many Australian animals show variation between the tropical north and the subtropical south, even within species.

See also Out of Africa(?), An Australian Spinosaurid and Mammals on Sciency Thoughts YouTube.