As the weather begins to cool, the ‘dig’ season starts for us (palaeontologists) as we venture off along the coast and into the outback heart of Queensland. Over the last ten years we have been investigating a series of fossil sites at South Walker Creek located near the town of Nebo, west of Mackay. It is here that we are finding some of Australia’s last tropical ice age megafauna.
Our dig team usually consists of palaeontologists, along with other scientists and specialists who contribute and volunteer their time. During the year of 2016 one of our volunteers, Noel Sands, who specializes in caving (and their fossil deposits!) called speleology, found a very large fossilized bone. Using an array of brushes and dig tools, Noel carefully excavated the sediment from around the bone to expose its shape and size. It was identified as a tibia (shinbone) [Sketchfab 1] from a kangaroo, but not just any kangaroo, the world’s largest species of kangaroo!
Once the position of the bone was established, we trenched around the specimen to create a pedestal so it could be isolated, with its surrounding sediment, from the rest of the dig site. The bone was then recorded and photographed in situ (the original place of deposition). We also place a temporary paddle pop stick [Sketchfab 6, 7)] with an identifying field number on the bone so it can be plotted in 3-D using a process called photogrammetry.
To begin the process of extraction, we first cover the bone and pedestal with foil to act as a protective layer. It is then covered with strips of wet newspaper, which provides cushioning for the jacket we are going to make to contain the bone. To make the jacket we use strips of hessian dipped in a plaster mix (casting plaster and water) and wrap them around the pedestal with the bone and wait for it dry. This is always the fun job!
Once the plaster jacket is dry, the field number and a directional north arrow are written on it so we know which specimen it is and its position in the site. The next step of the process is always tricky and is about getting it just right to roll the jacket over with the specimen kept in one piece. We use a hammer to bang in chisels at the base of the pedestal to loosen it from the underlying sediment. When it becomes loose it is ready to be quickly rolled over. If we have made a good jacket the specimen should stay all in one piece. On rare occasions we are not so lucky, but this time it went without a hitch! You can see this whole process in the video below, check it out!
Finally, the other side of the plaster jacket is sealed with the same plastering process to form a lid. Now the specimen is protected in a hard, egg-like shell to be transported back to the Queensland Museum and stored temporarily in the Geosciences collection with other unprocessed specimens awaiting preparation. There was also a distal tibia epiphyses (end cap) bone [Sketchfab 3] sitting on the shaft of the tibia and a bone shard [Sketchfab 4] nearby that were carefully collected so they were out of the way of extracting the tibia. We will be able to see if these bones are associated (connected) to the tibia.
Another challenge of the fieldwork is getting large jackets from the dig site back to the field vehicle. As the terrain is quite rough and our excavations occur in an eroded creek bed we cannot drive very close to the dig site. We have to use trollies, stretchers and manual handling to slowly walk the jackets with their specimens out of the dig site. Whilst excavating fossils by hand is exciting, it is also a lot of hard work. It involves good fitness, experience, precision, problem solving and most importantly team work.
Check out Part 2: In the Lab as we go behind the scenes to investigate the giant kangaroo leg further.
Megafauna are giant animals usually weighing over 44 kilograms (kg). Most megafauna are now extinct (no longer exist) and were closely related to living species of animals we see today. You have probably heard of the more commonly known megafauna species, like the saber-toothed cat and woolly mammoth from North America.
However, Australia is unique with its own megafauna ranging from huge and sometimes strange marsupials (mammals with a pouch), like the giant sloth bear-like Palorchestes to very large monitor lizards like the giant goanna, Megalania. There were giant wombat-like marsupials the size of a rhinoceros like Diprotodon, an array of giant kangaroos different to today’s species and a weird super-predator called Thylacoleo, which means pouched-lion. Australia even had giant, armoured tortoises with clubbed tails, land-dwelling crocodiles, giant constricting snakes and huge flightless birds.
Megafauna can also refer to species that weighed less than 44 kg, but resemble a giant version of a closely related living species. For example, the extinct ‘giant’ koala (Phascolarctos stirtoni) was larger than the living koala (Phascolarctos cinereus) and probably weighed under 15 kg. Others include a giant echidna, (Megalibgwilia), the Thylacine or Tasmanian Tiger and a larger relative of the Tasmanian devil, Sarcophilus laniarius. The term ‘megafauna’ is still used to refer to our largest living animals today such as the elephant.
Can you think of any other living megafauna or extinct?
The megafauna arose well after the extinction of the dinosaurs at the end of the Cretaceous Period, 66 million years ago. In Australia they reached their largest size during the Quaternary Period (2.58 million to 11,700 years ago). The rapidly changing climatic and environmental conditions created grasslands and open habitats favouring the worldwide evolution of gigantic animals. Towards the end of the Quaternary, extinctions of megafauna occurred with nearly two-thirds of Australia’s largest animals dying out, along with many smaller species.
There is a great debate in palaeontology (study of ancient life) and archaeology (study of human history) surrounding the big questions of why and how did the megafauna go extinct? Answers revolve around an extended period of severe climate change or human activity, or a combination of both, resulting in extreme changes to the environment. To answer these questions, we have to keep searching for the evidence and investigate more megafauna fossil sites – if they have been lucky enough to be preserved and can be found! Each individual site is a reflection of the different creatures and environmental conditions that existed within the ecosystem of that region representing a small piece of a bigger puzzle involving the whole of Australia and even the world.
Climate change here refers to the long-term, natural processes that can change the Earth’s climate such as its orbit around the Sun, changes in solar radiation, levels of greenhouse gases, and plate tectonics (movement of the Earth’s crust). These changes appear locally in the form of sustained changes in weather patterns, like decreases and increases in temperature, the frequency of droughts or flooding and overall intensifying aridity. Human activity during this time refers to hunting and disturbance patterns to the environment such as the burning of the landscape.
Today climate change includes anthropogenic drivers, like pollution from increased industrial activities of humans. Some of these include the burning of fossil fuels that generate extra greenhouse gases, pollutants and deforestation. These influence how the temperatures across the globe are regulated and drive global warming, a rise in the average temperature of the Earth’s climate system.
Megafauna fossils have been found around Australia and throughout Queensland. Those from the Quaternary Period have been found within sites in southern Queensland like the Darling Downs and Eulo. These sites are well known for the world’s largest wombat-like marsupial, Diprotodon optatum. Diprotodon would have browsed and grazed through the open woodlands and grassy plains of the downs and around the mud springs of Eulo, where on occasion they got stuck, leaving their bones for us to find tens of thousands of years later.
As we head north into the subtropics of central eastern Queensland we find fossils of megafauna from The Caves region near Rockhampton. The fossil remains of these animals that lived around and inside the cave systems have accumulated in cave chamber deposits. These deposits are unique as they record fossil fauna from different environments that transitioned through time from wet rainforests to dry open-arid habitats and then to today’s special vine thicket refugia (habitat supporting refuge). Here we find fossils of the extinct giant tree-kangaroo, Bohra, who is a larger version of today’s living tree-kangaroo species found in Far North Queensland and New Guinea.
Even further north in Queensland, west of Mackay, fossils of megafauna are being excavated from sites at South Walker Creek. These fossil deposits are rare because they preserve a tropical megafauna. Not many megafauna fossil sites have been found in northern Australia. Many of the fossil bones have puncture marks made by predatory crocodiles including the extinct giant freshwater crocodile, Pallimnarchus. These crocodiles would have inhabited the billabongs and creeks, hunting at their edge for unaware megafauna that would come to drink.
Research into the megafauna is helping us understand their responses to environmental change during the Quaternary Period and hopefully it will answer the many questions surrounding their extinction. If we can track down our past, we can better understand how our present has been shaped by the extinction of the megafauna and hopefully use that knowledge to prepare for the future impacts of environmental change.
Can you think of any impacts to our environments today that affects our living species?