Creature of the week #4: Diprotodon

marco_polo

Diprotodon, meaning "two forward teeth", was the first fossil mammal named from Australia (Owen 1838) and one of the most well known of the megafauna that inhabited the country. It has been found in numerous location right throughout the country, with the exception of Tasmania. Originally several species of Diprotodon had been named based on the size of the skull (Diprotodon australis, Diprotodon minor), but it is now believed that these are probably all males and females of one sexually dimorphic (different sized males and females) species, Diprotodon optatum.





The massive Diprotodon optatum largest marsupial that ever lived, and the last of the extinct, herbivorous diprotodontids. It inhabited Australia throughout most of the Pleistocene epoch, beginning its reign about 1.6 million years. Diprotodon was widespread across Australia when the first indigenous people arrived about 65,000 years ago, co-existing with them for thousands of years before becoming extinct sometime between 40,000 to 25,000 years ago. It is speculated that Diprotodon may be the origin of the legend of the bunyip, a large mythical creature from Aboriginal mythology.

At aproximately 3 metres in length, just under 2 meters to the shoulder, and up to 2800 kilograms in weight, Diprotodon, was only slightly smaller than a hippopotamus ( 4500 kilograms in weight) or rhino (3600 kilograms) which it superficially resembles. Its closest surviving relatives are wombats and the koala.



As browsing animals, feeding on trees and shrubs Diprotodon preferred semi-arid plains, savannahs and open woodlands, and is generally absent from hilly, forested coastal regions. As marsupials are not known to form large groups, It is unlikely that Diprotodon moved in large herds. There is evidence of either predation or scavenging of Diprotodon by the Pleistocene 'marsupial lion', Thylacoleo carnifex.

Diprotodon takes it name from its two forwardly directed lower incisors. A heavily built, large-bellied quadruped, its oversized skull was lightweight and filled with numerous air spaces. Some scientists believe that Diprotodon may have had a short trunk because of the retracted position of the snout. The limbs of Diprotodon were sturdy and pillar-like. The upper limb bones being longer than the lower ones.



The distinctive feet of Diprotodon were remarkably small for its size, and were inturned, similar to wombats. Other features it is known to share with wombats include a hairy coat and a backwards facing pouch.

The cause of its exytinction remains controversial with hunting, climate change and habitat destruction all proposed as possible explainations for its demise. The hunter theories suggest that human hunters killed and ate the diprotodonts, driving them extinct. There is some limited evidence to support this theory, but the limited nature of the evidence and the fact that they seemingly co-existed for 20,000-25,000 years seems to stand against this theory.

In support of the climate change theory, the last ice age produced no significant glaciation in mainland Australia instead there were long periods of cold and very dry weather, which may have finished the last of the diprotodonts. Some Diprotodon have been found with the not very nutritious saltbush plant in their stomachs suggesting possible starvation because of drought. Against this theory critics point out that they survived previous ice ages and that climate change peaked about 15-25,000 years after the extinction.

The final theory suggest that the practice of early Aborigines in starting fires regularly to drive game, as open up dense thickets of vegetation may have destroyed much of its habitat.

Diprotodon had a nice cameo in the BBC series Monsters we Met

** See next post down for video link**

Galvasean

Video embedding disabled? Booo!!!! Here it is:
http://www.youtube.com/watch?v=RjkPl7qtS8w&feature=player_embedded
Good choice and a very well written piece. Good to see our first land based mammal.

marco_polo

One of the problems for the human hunting theory was the uncertainty of the dates that the theory rests on, improved dating from one of the most important sites suggests that the overlap of humans and Australian megafauna may have been much shorter than previously believed and suggests that the megafauna extinctions had indeed occured by 40,000 years ago

http://www.sciencedaily.com/releases/2010/01/100121141109.htm

"Australia was colonised during a time when the climate was relatively benign, supporting the view that people, not climate change, caused the extinctions here."

But one site in western NSW -- Cuddie Springs -- stood out as an anomaly. Fossils of super-sized kangaroos, giant birds and the rhino-sized Diprotodon (the largest marsupial ever to roam Australia) were found in the same sedimentary layers as stone tools, leading some scientists to previously claim "unequivocal evidence" of a long overlap of humans and megafauna.

However, Professor Roberts -- the lead author of the Science paper "And Then There Were None?" -- says direct dating of fossils shows that the artefacts and megafauna fossils at the Cuddie Springs site were mixed together over many thousands of years, long after the giant animals had died.

"These results provide no evidence for the late survival of megafauna at this site," Professor Roberts says.

"Given that people arrived in Australia between 60,000 and 45,000 years ago, human impact was the likely extinction driver, either through hunting or habitat disturbance," he says.