Inside Australia’s Giants: Exploring Diprotodon

In this series, I’ll be exploring the anatomy of the Australian megafauna. This specific post will be focusing on the largest marsupial of all time; Diprotodon opatum, the 2.8 metric tonne, hippo sized marsupial that dominated the Australian landscape up until the latest Pleistocene. 

"I know you can read my thoughts boy... meow meow meow meow meow meow meow". Image via Gilbert Price

Their anatomy is super-duper weird; they filled out the “mega-herbivore” niche that was inhabited by gigantic varieties of Elephants (such as the Mastodons and Mammoths) on other continents. But their skull (despite being huge) was paper-thin in some sections; their feet are comparatively tiny and their incisors were the size of bananas. Chisel-sharpened bananas. Despite this, they played massive roles in Pleistocene ecosystems and were probably just as abundant as kangaroos in Australia today... 

"My, my, my, what BIG TEETH you have my dear". Diprotodon remains from lake Callabonna in Southern Australia. Image via Aaron Camens.

 Diprotodon was a strange animal for a number of reasons: 

1) Its bizarre, pancake like feet.

These feet were unusually small for its size; they were similar to modern wombats in that they were “in turned”. Its enormously fused anklebones were used to hold up the weight of this animal, but intensify the wacky looking nature of its feet. Were they using these heavily compressed feet/hands to dig up vegetation as they thundered across the parched plains? Their wrists were hugely inflexible, so probably not. When viewed against the rest of the body, (especially their huge, pillar like limbs) their feet look ridiculous. It’s most likely a vestige of their vombatiform (wombat-like) ancestry... 

"Mmmm, pancakes... *drool*"  (image via John R. Hutchinson)

The pancake in the flesh. Via the master palaeo-artist, Peter Trussler.

2) Its brittle skull morphology. 

What on earth was going on here? With a tiny brain, Diprotodon has an astoundingly unusual skull morphology for an animal of its size. Its skull has thin, almost brittle bone in a number of areas and a bizarre assortment of endocranial sinuses. Apparently it all has something to do with the huge muscles found in the jaw; it has a hugely exaggerated zygomatic arch (famous within the diprotodontid groups) at the back end of its jaw. The weight of this jaw and the demands of the large jaw adductor muscles (to allow chewing) would have had significant issues on the brain and surrounding braincase; Diprotodon bypassed these issues by implementing a number of extensive cranial sinuses... 

A skull from Bacchus Marsh, Victoria. From the basis of this skull and a number of other individuals from this site, it seems that they may have herded in matriarchal groups, led by an experienced female. Image via Erich Fitzgerald. 

 3) Its chisel sharpened banana teeth

There is no doubt that Diprotodon was a herbivore, a generalist browser eating shrubs low to the ground. Considering that skeletons of this creature have appeared all over the Australian continent, it would’ve taken advantage of almost any vegetation it could find (SIDENOTE: one skeleton from Lake Callabonna had the remains of saltbush in its abdominal region… radical!). Diprotodon was the first Australian fossil mammal to be described by the famous anatomist Richard Owen in 1838, on the basis of its teeth. They appear very “tapir”-esque, with horseshoe-like crushing basins on the molars for masticating harsh flora. But for myself, I lie in awe of its colossal incisors. The name “Diprotodon” literally means “two-forward-teeth” for the left and right incisor, which is larger than a banana and sharpened like a chisel blade. Along with a hugely exaggerated temporalis muscle (the one used for chewing) it would have been able to give an almighty bite to any predator or potential rival...

Chisel-sharpened bananas. The first, second and third incisor of Diprotodon. Image via ME. 

 These are just some of the anatomical features that make Diprotodon stand out above the rest. The quadropedal Diprotodontids were successful for over 30 million years, culminating in their largest form right at the end of their reign; the extinction of the largest marsupial ever is still hotly debated. It ranges anywhere between human causes (despite the native aborigines not having the “big game weapons” to take down such prey) through to variable climatic conditions (inland desertification) surrounding the final ice age... 


References

GILBERT J. PRICE; Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon (Diprotodontidae, Marsupialia), Zoological Journal of the Linnean Society, Volume 153, Issue 2, 1 June 2008, Pages 369–397

Murray PF 1991. The Pleistocene megafauna of Australia. In: Vickers Rich P, Monaghan JM, Baird RF, Rich TH Vertebrate palaeontology of Australasia. Melbourne: Pioneer Design Studio & Monash University, 1071- 1164
.





Comments

Post a Comment

Popular posts from this blog

The Evolutionary Dead-End Experiments of Crocodiles

Image
It was at this moment that Steve the fish realised he had made a dire mistake (Image via Andy Murch) Crocodiles are NOT living fossils...  They may look ancient, with a smattering of characteristics that make them look like non-avian dinosaurs, but as we dive back throughout the Mesozoic and come up for air in the murky waters of the late Triassic (roughly 230 million years ago), we find that the distant ancestors of the creatures we refer to as the heavily armored   “ Crocodylia ” (a group that includes all “true” crocodiles, caimans, alligators and gharials) look so completely different from their modern counterparts. Many early crocodylimorphs (a term that is used to include modern and long-extinct cousins of crocodilians) were completely terrestrial and include the ~230 million year old “ Trialestes ”, an animal that was originally interpreted as a basal dinosaur, due to its “un-crocodilian” upright stance. Thanks to the fossil record, w...
Read more

Inside Australia’s Giants: The Real Life Drop Bear

Image
Australia, 50,000 years ago.  55 million years of island isolationism created this graphic landscape. Terrestrial life in the "Great Southern Land" would be at its largest at the end of the Pleistocene.  Image via the world renowned palaeo-artist, Peter Trussler. The sun is intense. There's been no reprieve from the heat for the last few days, as sweat glistens on your forehead and flies land on every inch of your body. You're tired; but something has been preventing you from sleeping. For the last few nights, blood curdling screams from an other-worldy creature have pierced the dead silence.  This dry season has been an exceptionally intense one. You look around. Eucalypts dominate the surrounding parched red plain, with small interspersed shrubs and an assortment of weird animals. A small billabong is attracting the megafauna from all around. You see familiar faces on the far side of the water. A mob of red Kangaroos rest in the shade of small salts bushes...
Read more

Giant Filter Feeding Crocodiles from the Ancient Amazon

Image
Travel back in time to a world ruled by crocodiles. The Amazon jungle during the Middle – Late Miocene (6-10 million years ago) was a terrifying place. 12 metre long caimans such as Purussaurus , weighing more than 5 metric tons, rein supreme. One of the largest Crocodyliformes that ever existed: Purussasaurus (Purr-russ-a-saur-us) . That scale bar is 20 centimetres! This skull is the size of a human being! (Picture via Aguilera et al. 2006) Extreme niche partitioning of crocodile types occur here, with medium sized generalists (such as Melansosuchus - the modern Black Caiman - ) existing along-side crocodiles that specialised on hard shelled organisms such as crabs ( Globidentosuchus ) and by far the most bizarre that existed within this jungle, was the 12 metre long FILTER FEEDING caiman, the duck faced Mourasuchus .  Mourasuchus,  the crocodile that tried to be a baleen whale. That skull is HUUGE; the scale bar is 20 centimetres! (Picture via Cidade et al. 2017...
Read more