Pleistocene vertebrate trackways of Australia: documentation and significance at the continental scale

A project undertaken at the School of Biological Sciences, Flinders University, and supervised by Gavin Prideaux

Footprints are a valuable source of information about the presence and behaviour of the animals that made them. Sometimes, footprint-bearing sediment hardens into rock, so that the tracks are preserved for thousands or even millions of years. Palaeontologists, the people who study fossils, regard such tracks-in-stone as a special class of fossils, called trace fossils. 

We are studying tracks made by vertebrate animals, mainly marsupials but also birds and reptiles, that are preserved in geologically young rocks formed in the last hundred thousand years or so. We have previously found an extraordinary assemblage of tracks made by the enormous marsupial, Diprotodon, kangaroos and wallabies, wombats and possibly Thylacoleo (the marsupial ‘lion’) in the volcanic plains of Victoria. We have also recorded the tracks of small and large marsupials, and small and large birds in ancient dune deposits that occur along the coast of South Australia and Victoria.

With the support of the Hermon Slade Foundation, we expanded the study to Western Australia, in order to develop a continent-scale perspective on Australian late Pleistocene coastal ecosystems, as informed by the trace-fossil record. Western Australia’s enormous coastline has hundreds of kilometres of dune limestone similar to those in south-eastern Australia. We surveyed the most prospective outcrops for the presence of fossil trackways. All trackways found were carefully documented, photographed and analysed for the important behavioural and palaeoecological data they contain. Further, to determine the age of the trackways, we are processing samples of the host limestone by means of a technique called optically stimulated luminescence (OSL) dating.

Australian fossil vertebrate trackways are extremely rare and this project was the first of its kind in Australia. The data collected during this project will both to inform us of behavioural, anatomical and locomotory characteristics not preserved by skeletal fossils, and provide new palaeoecological information regarding the extinct Australian megafauna.

Project outcomes

Through three four-week field trips (in Sept 2011, Feb 2013 and Nov-Dec 2013) we surveyed approximately 2700km of coastline in western and southern Western Australia and 1200km of coastline in western South Australia. Prior to our survey, footprints had been reported in two localities along this stretch of coast. We documented the occurrence of over 200 new sites, ranging from single sets of prints to sites with hundreds of individual prints. These trace fossils represent at least 21 different taxa ranging in size from small beetles to the 2.5 tonne Diprotodon and include invertebrates, reptiles, birds and mammals. Many of the mammal (and some bird) footprints belong to extinct members of the Australian megafauna.

In addition we collected a substantial modern vertebrate trackway dataset, useful both for comparison with the trace fossils discovered, but also as a record of the fauna occupying modern coastal dune ecosystems.

Highlights of the trace fossil finds included trackways from large extinct herbivores like Diprotodon and Zygomaturus, several Thylacoleo (the marsupial lion) trackways, extinct short-faced, browsing kangaroo (sthenurine) traces, prints from the 250kg flightless bird Genyornis and numerous well-preserved Thylacine traces.

Casts of many of these trace fossils have been taken and are forming the basis for description of ichnotaxa (taxa described from the fossil footprints they left behind). Cutting edge computer software is being used for three dimensional modelling of trackways, in many cases resulting in the creation of a permanent 3-D record of the traces where no cast could be taken.

Preliminary dating from several of the sites suggests that the trace fossil assemblages span a significant period of time, the youngest being only around 20 thousand years old, and the oldest being at least 200 thousand.

Publications relating to the description of individual sites, description of ichnotaxa and interpretation of the palaeoecology of Late-Pleistocene coastal ecosystems on a continental scale (as viewed through the trace fossil record) are being prepared.

Captions for Figures

Figure 1. A diprotodontid trackway from D’Entrecasteaux National Park, WA.
Figure 2. Aeolianite cropping out at D’Entrecasteaux National Park.
Figure 3. Genyornis trackway preserved in beach rock near Ceduna, SA.
Figure 4. Thylacoleo trackways from Yalata Aboriginal Reserve, SA.
Figure 5. Investigating trackways on the Western Australian coast.
Figure 6. Thylacine trackway from near Margaret River, WA.
Figure 7. OSL sampling at Innes National Park, SA.
Figure 8. Casting of fossil Macropus (kangaroo) tracks near Margaret River, WA.

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