My team and I have just had a new study published that that looked at the question of migration in a species of giant, now-extinct, Ice Age megafauna of Australia.
The beast under the ‘microscope’ is Diprotodon optatum, famous for being the largest marsupial that ever existed. It stood 1.8 metres tall at the shoulder and weighed in at around 3,000 kg.
A herd of Diprotodon being stalked by the giant lizard, Megalania, while a couple of megafaunal kangaroos look on (image: Laurie Beirne)
Diprotodon was one of the very first fossil animals ever described from Australia. Subsequent fossil records show that it had a near cosmopolitan distribution across Ice Age Oz, plus was one of the last surviving members of the megafauna.
But there’s a lot that we just don’t know about this animal, such as how it responded to seasonal changes; what its ecological role was; it’s basic biology… important questions that are critical in helping us understand why we don’t have Diprotodons anymore.
What we did
Our new study focussed on the life and times of an individual that once called the Darling Downs of southeast Queensland its home. We wanted to know what it ate, if it was a migratory species, and how it responded to changes in its environment.
Unlike some of their placental cousins, most modern marsupials don’t migrate at all. Some species, such as Red kangaroos (Macropus rufus) occasionally exhibit ‘nomadic’ migration where an individual or two will leave a home range, but with no specific plan or intention to return.
But what about Diprotodon? Weighing in at three tonnes, it’s more than 30 times the mass of the largest living marsupial, and likely had a very different ecological role when alive.
We applied a variety of geochemical analyses to a Diprotodon incisor tooth that we had borrowed from the Queensland Museum.
What we found
Without getting into the nitty gritty details, our study yielded some fascinating results. Firstly, our Diprotodon was clearly a seasonal migrant. It would undertake massive round-trips of up to 200 km per year as it tracked its preferred food source (basically, a combination of different species of grasses and leaves).
This is known as ‘two-way’ migration and is an evolutionary response to annually fluctuating resources.
Our discovery of such migration is a first for any marsupial living or extinct. That’s wildly fascinating in itself because marsupials have been around for a very long time. In fact, marsupials and their broader cousins, the metatherians (the group that includes all modern marsupials, but not placental or egg-laying mammals), have been on Earth for at least 160 million years. And until now, none have been known to have conducted such migration.
But perhaps more importantly, our data suggest that Ice Age Australia was just so ecologically different to anything that we’ve previously imagined.
In fact, the palaeo-ecosystem that we envisage seems more like the modern Serengeti than anything that we have Downunder today.
Some burning questions
Zebra are migrating mammals of East Africa’s Serengeti
At the end of the day, we’re left with even more questions than what we started out with. Which other megafaunal species migrated? What were the consequences of their removal from Ice Age ecosystems? And especially, what are the implications for understanding Australia’s modern ecology?
These are major questions that need to be addressed, and will form the focus of future investigations.
We are massively appreciative of all the institutions that supported this research: The University of Queensland, University of Rochester, Southern Cross University, and Griffith University. Huge thanks to the Queensland Museum (and especially Kristen Spring) for their support, Nathan Siddle for making the 3D model, and the Australian Research Council for funding this research.
Gilbert Price
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