A Crime scene of the past – investigating tropical ice age megafauna

By Rochelle Lawrence, Palaeontological Research Assistant, and Scott Hocknull, Senior Curator, Geosciences, Queensland Museum

In 2008, an extraordinary discovery was made at South Walker Creek, located near the town of Nebo, west of Mackay in Queensland, Australia. Traditional owners of the area, the Barada Barna people, were conducting a cultural heritage survey for the South Walker Creek Mine when they came across some interesting bones. These bones were not the usual white colour, like those of cows you find in the paddock, nor were they light in weight or becoming brittle from exposure to the sun. They were dark coloured, a little heavier than usual and quite solid in form.

We have found the white, brittle bones of modern cows and sheep on many of our fossil surveys. Image Credit: Rochelle Lawrence.
 A fossil osteoderm (bone plate) from the scales along a crocodile’s back and a piece of bone below that was first found at South Walker Creek. Image Credit: Andrea Bull.

The bones were fossils! Fossils are the remains or traces of organisms (animals and plants) from a past geological age. Most fossils form from the bones and hard parts of animals and plants, but sometimes in rare conditions the soft parts, such as flesh and organs, can be preserved. The feathers, fur and stomach contents of animals have also been preserved, as well as small creatures, like insects, trapped in the sticky sap of trees, which has hardened into amber over millions of years. Trace fossils can include animal droppings, burrows, eggs or footprints, which can tell us a lot about the animal’s habits. They are all evidence of once-living things!

Brachiood fossil found at Homevale National Park on 29/09/2008 by Josh Moulds.

Fossils are found all over the world, but they only represent a few of the many organisms that have existed on the planet. Special conditions are required for an organism to become a fossil and survive the changes within the Earth’s sediment through time. Firstly, an organism has to be buried by sediment, such as mud and sand, which is usually washed in by water. The next stage of fossilisation depends on the organism itself and the environmental conditions. The bones from South Walker Creek have undergone a process called (per)mineralisation. Minerals from the soil and water in the creeks enter the cracks and pores of the bone making it harder over time and giving it a stony appearance.

White cards with field numberes were used to indicate the fossil bones found within the ancient creek. The one on the left is an arm bone (humerus) from a giant kangaroo, which has a whole other story – stay tuned with future blogs. Image Credit: Josh Moulds.

The environmental officers of the mine contacted the Queensland Museum where they were put in touch with palaeontologist, Dr. Scott Hocknull, who studies fossils of ancient life. Dr. Scott and his team worked with the traditional owners and mine officers to conduct natural heritage surveys, looking for more fossil remains and traces of past ecosystems within the geological landscape (geology) along the Walker Creek system.

The team surveys the ancient creeks and floodplains of the area looking for other fossil sites. Image Credit: Josh Moulds.

On inspection of the fossils, Dr. Scott identified them belonging to extinct giant creatures, not dinosaurs, but megafauna! The megafauna we refer to here occurred during the ice ages of the Quaternary Period from 129,000 to 11,700 years ago. An exciting find was waiting for them in the form of a partial skull from the giant wombat-like marsupial, Diprotodon optatum.

The tooth rows from a skull of the giant wombat-like marsupial, Diprotodon optatum, were eroding out of the ground. Image Credit: Josh Moulds.

The megafauna fossils from South Walker Creek mostly represent †extinct species, some of which are new to science, along with a few extant (living) species that survive today. We have found predators such as crocodiles †Pallimnarchus (giant freshwater crocodile), † ‘Quinkana’ (terrestrial crocodile) and Crocodylus (saltwater crocodile), the giant goanna †Megalania (Varanus priscus) and the marsupial ‘lion’ †Thylacoleo.

A fossil tooth from a crocodile found while surveying. Image Credit: Josh Moulds.

These predators would have preyed on the herbivores (plant eaters) that they lived with, such as the giant wombat-like marsupial, †Diprotodon optatum, giant wombats like †Phascolonus gigas, the strange giant sloth bear-like marsupial, †Palorchestes, and kangaroos, including the giant forest wallaby, †Protemnodon, a short-faced kangaroo (†Sthenurine), the red kangaroo (Osphranter rufus), a giant wallaby (†Notomacropus) and a giant deer-like kangaroo (†Macropus sp.). 00Rare fossils, including eggshell, of the emu (Dromaius novaehollandiae) have also been found.

Dr. Scott excavates the tooth rows and partial skull of the Diprotodon to carefully remove it from the ground. Image Credit: Josh Moulds.

In among the megafauna bones we also find small fauna of both aquatic (water-dwelling) and terrestrial (land-dwelling) species, along with the fossil impressions of leaves and seeds from the plants that grew in the environment at the time of the megafauna. These delicate remains are rarely preserved in fossil sites of this age and are especially uncommon in the tropics making these sites extra special for palaeontologists. Since 2008, teams have undertaken fieldwork to survey, salvage and excavate fossil sites at South Walker Creek and this work continues today.

Dr. Scott and field volunteer, Noel Sands, carefully carry the partial skull of Diprotodon out of the site as if it were the Ark of the Covenant from Indiana Jones. Image Credit: Josh Moulds.

The fossil discoveries from South Walker Creek are exciting because little is known about the megafauna from the tropical northern regions of Australia compared to those that have been studied in southern Australia. The site is significant as it preserves fossil evidence that is very close to the time of the megafauna’s ultimate extinction in Australia. By studying the site, we are finding answers to our questions surrounding the evolution and extinction of megafauna. Documenting the responses of megafauna to past environmental change is important to better understand the impacts of future change on our living species.

The team celebrate their exciting fossil finds and Diprotodon treasure. Image Credit: Queensland Museum and BHP.

Stay tuned for future blogs on South Walker Creek fossils as we take you behind the scenes and delve deeper into the past of these tropical ice age megafauna.

Project DIG is a partnership between Queensland Museum and BHP that will digitise and scan our collections and research for people worldwide. Check out our Tropical Megafauna in 3D!

Top Image – The main site of the South Walker Creek megafauna fossils where we are excavating their remains within an ancient floodplain. Image Credit: Josh Moulds.

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