The Last Interglacial – Last of the Dryland Megafauna

Australia: The Land Where Time Began

The Last Interglacial – Last of the Dryland Megafauna

Significant guilds of dryland megafauna were restricted to the southern part of the Lake Eyre basin, mainly in the area of Cooper Creek by the last interglacial. Associated with the upper Katapiri Formation, this regional fauna collapsed about 65 ka, contracting to the desert margins, were some of the megafauna persisted until 50-45 ka.

The megafauna of the Late Quaternary had a distribution that was predominantly southeastern, as shown by a recent review of the distribution of these species across the continent, the greatest diversity of species being in the woodlands, plains and forests of southeastern Australia (Webb, 2008). The arid zone appears of have been largely empty of megafauna by 132-115 ka, apart from the areas of Lake Eyre and Cooper Creek. Across the western interior and along the west coast there have been isolated finds of Diprotodon optatum, but they all appear to be much older than the last interglacial, though they haven’t been dated. In this context, the rich fauna recovered from the Upper Katapiri sediments is an extension of the megafauna from the southeast, from the desert margins along major river systems of the inland into the region of Lake Eyre.

The Katapiri Fauna

The Katapiri Fauna provides at the regional level a picture of a rich savannah environment in the last interglacial, that is comprised of a mosaic of habitats that includes riparian forests and woodlands, floodplains that are seasonally flooded, back swamps and deep waterholes that are permanent, and open drylands that are covered by grasslands, chenopods and Callitris pine woodlands. Smith suggests that J. W. Gregory may have been thinking of the Serengeti when he made the comment ‘when I noticed the richness of the soil, I could not but think what a paradise this country would be if only it had an East African rainfall’ (Gregory, 1906: 112).

Webb (2009; see also Tedford & Wells, 1990) has given the most comprehensive listing of the upper Katapiri sediments. The major macropods present are:

· The short-faced kangaroos, Procoptodon and Sthenurus,

· other large herbivores include Diprotodon optatum, and the giant wombat, Phascolonus gigas,

· Arboreal species such as koalas Phascolarctos and possums Trichosurus vulpecula

· Smaller taxa characteristic of arid-zone faunas such as bandicoots Isoodon obesulus, Macrotis lagotis, rat kangaroos Bettongia Lesueur and hare wallabies Lagorchestes leporides.

· Large flightless birds including the emu Dromaius and the much larger Genyornis, which has been estimated to have weighed up to 275 kg.

A range of carnivores and scavengers were supported by this herbivorous fauna such as;

Megalania prisca, a large varanid lizard,

Thylacoleo carnifex, the marsupial lion, Thylacinus, Thylacines,

Palimnarchus, the freshwater crocodile, which is represented in these fossil deposits by many cranial fragments, scutes, teeth and vertebrae. Its effectiveness as a predator in the waterways of the inland has been recorded by the marks of its teeth on Diprotodon bones.

Also in these channels and waterholes was a range of fish, freshwater mussels and chelid turtles. The presence in these assemblages of fish vertebrae indicate that some individual fish weighed up to 36-50 kg (Webb, 2009).

According to Smith there are not many dryland fauna that allow comparison with that from the upper Katapiri. The caves on the Nullarbor Plain have spectacular pitfall assemblages that have been dated to the Middle Pleistocene, at least 780 ka – 200 ka (Prideaux et al., 2007). These represent an arid-adapted fauna that is older, and occupy a mosaic of woodland and shrubland. It has been shown that comparisons across a number of assemblages from the Middle Pleistocene that all of these are dominated by browsers, but those from the Nullarbor and Lake Eyre basin characteristically have more grazers and mixed feeders than do faunas of woodland and forest, as well as fewer arboreal species. Smith suggests it seems likely that for the Katapiri fauna of the Late Pleistocene would also have been the case.

Lake Callabonna

It is suggested that as the Lake Callabonna area is a more marginal environment the fauna in this area is more limited than that in the Cooper basin. The fossils from Lake Callabonna have been OSL-dated to 75 ± 9 ka (Roberts et al., 2001). A minimum age of 53,400 BP has also been reported (Gillespie et al., 2008) for the gut contents of a Diprotodon. The Lake Callabonna area was a shallow saline lake that was seasonally dry, surrounded by saltbush and Cypress pine, at the time diprotodonts were in the area, with eucalypts lining watercourses that drained into the lake. It is shown by trackways and footprints that have been preserved as carbonate-cemented imprints that well established traffic crossed the lake (Telford, 1984). At a time when the lake level was low diprotodonts were trapped in the mud while attempting to cross the mudflats to nearby mound springs.

Population Ecology

According to Smith s range of sources has provided information about the ecology of these animals. It is shown by distribution patterns within the Lake Eyre basin (Webb, 2009) that the main channels and flood plains were favoured by most species (11-17 species), the highest diversity of species being along Cooper Creek. In arid terrestrial habitats away from rivers there are only 7 species that are regularly found, including Diprotodon and Genyornis which are known to be wide-ranging species. It is suggested by the distribution of Procoptodon fossils that have been found that species could also forage in the arid backcountry.

Carbon isotope analysis of tooth enamel from the upper Katapiri confirms that Diprotodon was a mixed feeder, consuming both C3 and C4 plants (δ¹³C - 18.8 ± 3.0) (Gröcke, 1997). Sthenurus was a browser with a diet of C3 shrubs (δ¹³C -24.3 ± 0.9), and is suggested by Smith to have probably been more restricted to woodlands and riparian habitats. Procoptodon has been shown by other isotope work to have specialised on browsing on chenopod vegetation (Prideaux et al., 2009), while Genyornis selectively ate C4 plants, though it was a mixed feeder (Miller et al., 1999; Miller, Fogel & Magee et al., 2005). The dietary signature of saltbush has been observed in Genyornis eggshell in temperate areas that are well beyond the distribution of C4 grasses, therefore it must have included saltbush in its diet (Smith, 2009a). Gut contents of a Diprotodon has been found at Lake Callabonna which provided direct evidence of this giant marsupial. It has been recorded by Stirling that loosely aggregated globular masses of what are believed to be leaves, stalks, and small twigs of some herbaceous or arboreal plants’ (Stirling, 1900: XII). They were originally tentatively identified as ‘Salsolaceae’ or ‘the allied orders of Amarantaceae or Nyctagineae’, which indicating these are most likely to be a chenopod. According to Smith recent analyses has confirmed this, by the use of x-ray analysis and stable isotope measurements, which demonstrated that the material is Atriplex (saltbush), which is C4 halophyte shrub (Gillespie et al., 2008).