Discussions on the history and historiography of Australia's New England

Monday, October 02, 2017

When the Diprotodon ranged New England and the Darling Downs

The Diprotodon, a three-tonne marsupial up to 1.8 metres tall and 3.5 metres long, was one of the largest animals to roam Sahul, the prehistoric continent that became Australia.

Many mysteries remain about the Australian mega-fauna including the Diprotodon.  Now a study published in the journal Proceedings of the Royal Society of London B. by a team led by Gilbert Price has revealed intriguing if brief details about the pattern of their life.

The article abstract is set out below. Further comments follow the abstract. .
Seasonal two-way migration is an ecological phenomenon observed in a wide range of large-bodied placental mammals, but is conspicuously absent in all modern marsupials. Most extant marsupials are typically smaller in body size in comparison to their migratory placental cousins, possibly limiting their potential to undertake long-distance seasonal migrations. But what about earlier, now-extinct giant marsupial megafauna? Here we present new geochemical analyses which show that the largest of the extinct marsupial herbivores, the enormous wombat-like Diprotodon optatum, undertook seasonal, two-way latitudinal migration in eastern Sahul (Pleistocene Australia–New Guinea). Our data infer that this giant marsupial had the potential to perform round-trip journeys of as much as 200 km annually, which is reminiscent of modern East African mammal migrations. These findings provide, to our knowledge, the first evidence for repetitive seasonal migration in any metatherian (including marsupials), living or extinct, and point to an ecological phenomenon absent from the continent since the Late Pleistocene. 
Source: Seasonal migration of marsupial megafauna in Pleistocene Sahul (Australia–New Guinea) Gilbert J. Price, Kyle J. Ferguson, Gregory E. Webb, Yue-xing Feng, Pennilyn Higgins, Ai Duc Nguyen, Jian-xin Zhao, Renaud Joannes-Boyau, Julien Louys
Proc. R. Soc. B 2017 284 20170785; DOI: 10.1098/rspb.2017.0785. Published 27 September 2017
The articlis behind the paywall. However, Dr Price provided details in a piece in The Conversation, Giant marsupials once migrated across an Australian Ice Age landscape (27 September 2017). For reasons that I will explain in a moment, I think that it is a little over-egged. But first, a methodological note.

The chemical signature of the foods that an organism eats becomes fixed into its teeth when they form. But, as Dr Price noted, it’s also true that “you are where you ate” becomes fixed, especially if you are a plant eater. The geochemistry of the soils where plants grow also becomes incorporated into a herbivore’s teeth. If that particular geochemical signal varies within a given tooth, it would imply that the individual fed across different geological regions when alive.

To study this, Dr Price and his team selected an upper incisor from a Darling Downs fossil and drilled numerous samples from the tough, crystalline outer enamel for a geochemical study. When this was subjected to chemical analysis, the results suggested that that the Diprotodon had displayed migratory tendencies, moving from north to south and back in a 200 mile range across the Darling Downs. Quite remarkable really, both in terms of the science and the results.

I said that the results were perhaps over-egged. As you will see when you read the piece, he compares this to the migratory patterns of the wildebeest, noting that it is the first time that this pattern has been established for marsupials and then extending his argument to establish a global significance for the find. The Darling Downs becomes the Serengeti of Australia.

The comparison of this with wildebeest migrations is a bit of a stretch. The distances travelled by the wildebeest dwarf 200k, while not all wildebeest are migratory. It does appears correct that marsupials do not display migration patterns as such. However, kangaroos are semi-nomadic and will move in search of food and water. The ethnographic evidence on the western slopes and plains suggests that during wet periods the Aboriginal population dispersed, concentrating around water sources during dry periods. This appears to reflect movements in the distribution of animals as well as vegetable foods and water.

The Diprotodons were very big animals who displayed herd behaviour. I would have thought that they would have to keep moving at least slowly or they would have just eaten out the the local vegetation. Over a twelve month period,. they could well have covered considerable distances. It makes sense that that movement should adopt a regular pattern, one that presumably had to take the existence of other herds into account as well as seasonal changes. The movement pattern averages a bit over a k a day if they moved 400k in a year. This doesn't rule out migratory patterns, the analysis of the teeth would appear to support that, simply that there are other explanations. It would be interesting to know how much a Diprotodon had to eat! This would tell us how soon they might out-eat a patch.

If we move from the macro-level that concerns Dr Price to a more regional and micro-level, Dr Price has given us a piece of information that we have never had before.

South of the Darling Downs, we have Diprotodon remains from Tambar Springs, Mooki River, Cox's Creek, Lime Springs, Redstone Creek and Cuddie Springs. They were clearly widely spread. The Liverpool Plains was, like the Darling Downs, an apparent hotspot. What Dr Price has done is to provide a piece of range data that may allow us to model the range distribution and behaviour of an extinct species in a particular area, the Western slopes and immediate plains. I think that's rather important.

There are also some real dating issues not well picked up in The Conversation piece. We don't have a lot of good dates. From what I know of the dates, I think the LGM marked the end, although it may have occurred earlier. Whatever the end date, it seems to me that there is now a very clear overlap between Aborigines and megafauna.

My thanks to regular commenter JohnB for inspiring this story.

Update 7 October 2017

Ian Vasey (@Ianvasey53) pointed me to this 1925 Armidale Chronicle story on the discovery of parts of a Diprotodon at Armidale. The Australian Museum piece on the animal provides a very good overview.

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