Australian Megafauna A-Z: D is for Diprotodon
This instalment in my A-Z of Australian megafauna series has been long overdue (the last one was written way back in October 2013) so, without further ado, we’ll get straight into talking about it! This time, it’s one of the most, if not the iconic Australian megafauna taxon, Diprotodon. Read on, for a brief introduction to the quintessential extinct Aussie.
The name Diprotodon means “two front teeth” and refers to the enlarged, constantly growing first incisors of the animal. It was the very first fossil mammal to be described from Australia and it was named by none other than the man who coined the name dinosaur, Richard Owen, in 1838.
It still remains uncertain exactly how many species of Diprotodon there were, estimates vary between one to eight depending on who you talk to.
Edit: This is what happens when you use older texts as references and don't check for more up to date research! Shortly after publishing this post I got a comment from Dr. Gilbert Price, one of the foremost experts on Diprotodon in the world, who let me know the current situation concerning the taxonomy of Diprotodon. The comment can be seen at the bottom but I've also decided to add it here. Thanks for the info Dr. G!
"[T]he jury is no longer out on the number of species known- only one is today formally recognised, D. optatum (please note that the Wikipedia article on Diprotodon needs a major overhaul!). The other eight species (or even up to 20 according to some writers!) are simply synonymous with the big guy. The problem with Diprotodon taxonomy really came about in the early days of palaeontology in Australia.
Sir Richard Owen described the first specimen in 1838, attributing the name D. optatum. He later changed the name in the 1840’s to D. australis (and even referred the original 1838 specimen to ‘australis’), seemingly forgetting that ‘optatum’ was already out there and published.
A similar issue is also found with D. annextans and D. longiceps, by McCoy (former director and curator of the National Museum of Victoria) in the 1860’s- both names are based off the same specimen.
Taxonomic problems were further compounded with the description of other Diprotodon species in newspapers in the 1870’s (newspapers can actually constitute a published work in eyes of the International Commission of Zoological Nomenclature, providing that the description meets a few other criteria too). Gerrard Krefft (Australian Museum in Sydney) named both D. loderi and D. bennettii in ‘The Sydney Mail’ newspaper. Not being aware of Krefft’s work, Owen, who was based in England and probably not an avid reader of the Sydney Mail (!) later described another new species and named it D. bennettii. Obviously, he was not aware that Krefft had already given the name to another bunch of Diprotodon fossils.
Confusing things even more, Diprotodon comes in two different sizes, sometimes referred to as the ‘large form’ and ‘small form’, the later including the species D. minor, described by Huxley in the 1860’s.
There was a real tendency for the early researchers to slap a new name on just about every specimen that came out of the ground. At a time before it was easy to travel around to different museums to look at fossils, and the internet to discover the plethora of published research, I guess it’s quite understandable how the Diprotodon taxonomic issues came about.
I had the pleasure of looking into this problem a few years back. During the course of pulling my hair out, I was able to unravel the longstanding taxonomic problems and came up with the interpretation that there was only one recognisable morphospecies, D. optatum. In addition to the all the nomenclatural problems, and two size classes (which I interpret to represent sexual dimorphism), D. optatum is also morphologically variable in some taxonomically useful characters.
Later, working with a local farmer on the Darling Downs in Queensland, we came across another Diprotodon individual, with left and right sides of the palate preserved. If you looked at both sides separately, you’d think that two species were represented- D. minor and D. optatum! So, there can be a huge range of variation, even within the same individual!
More details about all of this can be found here-
Taxonomy and palaeobiology: http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2008.00387.x/abstract
Body size evolution: http://onlinelibrary.wiley.com/doi/10.1002/jqs.1285/abstract
Morphological variation: http://www.tandfonline.com/doi/abs/10.1080/03115511003793553#.U0dillcXLL4
And of course: http://www.diprotodon.com
Now, as for the extinction question… don’t get me started!"
Diprotodon is so ubiquitous because of its large size. It is the largest marsupial to have ever lived, with the largest specimens reaching over three metres long and standing two metres tall at the shoulder and has been nicknamed the marsupial rhino because of its similarity in shape and size to the perhaps more familiar placental mammal. It lived throughout the Pleistocene and went extinct around 30,000 years ago, meaning that they would have co-existed with Australia’s earliest inhabitants. Indeed, some aboriginal rock paintings are purported to depict these extinct animals. Several theories have been put forward as to the cause of their demise including human hunting or habitat alteration (through burning off of vegetation) and climate change. It is more likely to have been a combination of several factors that caused these animals to go extinct rather than any one single reason.
In addition to skeletal material, trackways made by Diprotodon were found at Lake Callabonna in South Australia, giving a glimpse into the behaviour of this animal. There have been several cases of groups of Diprotodon being found together, having perished in drought conditions. The skeletons found at Lake Callabonna suggest that the animals became trapped in the mud and never escaped.
These animals were herbivorous and its teeth were well suited for grinding down plant material. The biomechanics of how these creatures did this is the subject of the PhD thesis of a colleague of mine, Alana Sharp. So when Alana publishes her research you can expect to read about it here!
Hopefully there won’t be as quite a large gap between this post and the next one in this series, but with a PhD to do, who knows. Next up is the letter E, whoever guesses the next animal to be discussed wins 10 science points! Get guessing!