Discovering the world’s largest kangaroo- Part 1: In the field

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

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.

The dig team excavate megafauna bones at the main fossil site on an ancient floodplain. Image Credit: Rochelle Lawrence.

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!

Using a palaeontologist’s tool kit to remove the sediment and find the extent of the bone. Image Credit: Rochelle Lawrence.

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.

Scott and Rochelle doing the ‘photogrammetry shuffle’ where they take overlapping photos at different heights and angles of the exposed bones across the entire dig site. These photos are uploaded to special software to reconstruct them in 3-D, kind of like a 3-D puzzle. Image Credit: Clare O’Bryen.

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!

The large tibia bone on the pedestal ready to be jacketed.

Scott, Christina and Natalia have fun plastering the specimen. Images Credit: Rochelle Lawrence.

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!

Scott using a hammer and chisel to slowly wedge the plaster jacket away from the ground.

Noel and Scott sit happy and proud with the successful roll over of the plaster jacket. Images Credit: Rochelle Lawrence.

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.

Scott and Christina make the lid to the plaster jacket so it is sealed and protecting the specimen inside on its travels back to the museum. Image Credit: Rochelle Lawrence.

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.

Scott and Peter are tasked with transporting the large plaster jacket across the bumpy terrain to the field vehicle using a trolley. Image Credit: Rochelle Lawrence.

Check out Part 2: In the Lab as we go behind the scenes to investigate the giant kangaroo leg further.

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 dig team sit proudly around the tibia of the world’s largest species of kangaroo, all ready to be extracted. Image Credit: Rochelle Lawrence.