18 December 2015

18. Naracoorte

Thylacoleo, the "marsupial lion," at Naracoorte
Location: South Australia
Age: Pleistocene-Holocene (530,000 years ago - Recent)

And so we arrive in the Pleistocene, the "Ice Age" of popular imagination and the culmination of the gradual cooling of the Miocene and Pliocene.  While the planet's temperature was lower on average than it had been since well before the evolution of the dinosaurs, Earth was not covered entirely in ice and tundra.  Periods of glacial advance were followed by warmer periods, this cycle driven largely by alterations in orbital dynamics.  Many parts of the globe remained glacier-free even during colder intervals, and prominent among these areas was Australia.  While never glaciated, the continent's environments were radically changed by climatic cooling and drying, a process that we have already seen illustrated in the north at Riversleigh.  In the far south, the Pleistocene landscape was dominated by eucalyptus woodlands, an environment still familiar to modern visitors to the region.  Unlike today, these woodlands were populated by Australia's endemic megafauna, a term used to describe the large mammal (and in Australia's case, reptile and bird) faunas of each continent during the Pleistocene.  At Naracoorte in what is now South Australia, a series of caves acted as natural pitfall traps into which animals occasionally fell, a process that over several thousand years led to meters-thick megafauna bone beds (this style of preservation is a recurring theme in Pleistocene lagerstätten, another excellent example being Wyoming's Natural Trap Cave).  In fact, animals of all sizes are preserved at Naracoorte, including some personal favorites, the shrew- to rat-sized carnivorous dasyurid marsupials.  However, the stars of the show are the impressive number of organisms to which the adjective "giant" can be appended: the giant snake Wonambi, the giant lizard Megalania, the giant bird Genyornis, the giant kangaroo Procoptodon, the giant-by-any-standards Diprotodon, and so on.  As with megafauna across the globe, there are several Naracoorte animals that have no close living relatives and, in this case, defy comparisons to anything alive today, the prime examples being the bizarre (even by Australian standards) Palorchestes and Thylacoleo.  Perhaps the most widely asked question about megafauna on any continent is why so few of them are around today.  Was it a result of changes in the ever-cycling Pleistocene climate or of the spread of our own species?  Spanning as it does the whole of human occupation of Australia, Naracoorte is one place that lends itself to addressing this question, but it is in North America that the debate has reached its most intense.

Visit: Naracoorte Caves National Park south of Adelaide, part of the same World Heritage Site as Riversleigh, allows visits to some of the fossil-bearing caves.
Fossils: The official repository for Naracoorte material is the South Australian Museum in Adelaide, though I believe a fair amount of material has made its way to the Australian Museum in Sydney as well.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: Not that I'm aware of.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

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