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What Lies Beneath

Gavin Prideaux excavating an extinct kangaroo skull from beneath the Nullarbor.

Gavin Prideaux excavating an extinct kangaroo skull from beneath the Nullarbor.

By Stephen Luntz

A small pit in the ancient Nullabor woodlands proved to be a deathtrap for ancient Australian marsupials, birds, reptiles and frogs – and a treasure trove of intact skeletons for palaeontologists.

On an August 2011 expedition to a cave beneath the Nullabor, palaeontologist Dr Gavin Prideaux provided the world with an online opportunity to learn what really occurs on a dig. The richness of the site ensured that visitors to his temporary blog had a chance to experience important developments in our knowledge of Australia’s ecological history.

The Nullabor cave is remarkable, both because it contains millions of years of vertebrate history and because the skeletons to be found there are so often intact.

The land above the cave was once open woodland or savannah. Prideaux explains: “A lot of marsupials are active at night, and they wouldn’t see a small hole about a metre across”. The hole is a pitfall trap, with the bottom 20 metres below, providing no opportunity for an animal to escape.

While such a space could be expected to reveal a rich source of bones, the cave in question offers more. There are several ledges on the way down, and it seems that many of the animals were not killed by the fall. After plunging the last few metres they picked themselves up and walked off to other parts of the large space to die. Consequently there are many intact skeletons rather than a confusing jumble of bones.

So many examples of the so-called marsupial lion (Thylacoleo carnifex) have been found in this and neighbouring caves that they have been given the collective name the Thylacoleo Caves. There is also a wealth of bones from giant kangaroos, giant wombats and even Tasmanian devils, which once inhabited the mainland. Reptiles and rare examples of frogs from an era when the area was wet enough to support amphibians enhance the collection.

“One cave has a record that goes from 200,000 years to a million years,” Prideaux says. “We’re looking at how the composition of the community has changed.”

The cave is also rich in bird skeletons. “Even today, kestrels nest in the entrance,” Prideaux says. “The cave is so large it breathes in when there is a high-pressure system above it and out when there is a low-pressure system. The air can race in and out at 100 km an hour. Birds come in following the air stream, or are swept in. Once inside they have trouble finding the tiny spot of light on the ceiling. It’s one of the most diverse bird sites in Australia.”

Prideaux blogged the experience on the Western Australian Museum’s website. “This was only possible because we were accompanied by a film crew who brought a satellite dish,”Prideaux explains.

The process offered an insight into the difficulties of identifying species under such conditions, particularly when the on-site team lacks experts in the species discovered. One set of bones was initially thought to be from a wedge-tail eagle, but is now considered “more likely from a giant mallee fowl.”

Prideaux describes this as an example of the dangers of trying to classify material based on the “crappy low-res photographs” they were able to transmit to experts while still inside the caves. A wedge-tail might be more charismatic, but the finding extends the mallee fowl’s known range by more than 1000 km, making it more scientifically significant since wedge-tails of a similar vintage have previously been found in the same cave.

The decision to blog the expedition came about because palaeontology attracts enthusiasts in a way few sciences can match. “Most palaeo people are passionate very early on,” Prideaux says. “There are people in my lab who wanted to be palaeontologists since they were 3 years of age. I have 13-year-olds volunteering who know as much about palaeontology as I did in third year at university.”

Prideaux is keen to tap into this enthusiasm, both to develop a future pool of scientists and as a way to draw in volunteers. Some of his students have established the Flinders University Palaeontology Society, which gives amateurs an opportunity to come on digs or process samples. For those who cannot attend a dig, the opportunity to watch it unfold in real time is the next best thing.

Yet Prideaux was not one of these young devotees. Although he was interested in palaeontology, it was just one of the fields of science that excited him at school, and he enrolled in a general science degree at Flinders University unsure where it would take him.

Prideaux was fascinated by the palaeontology he studied as an undergraduate at Flinders, but says he chose the field because it is so multidisciplinary. “I liked earth sciences and geology, botany and plant adaptations. I loved learning about animal anatomy.” Palaeontology gave him the opportunity to combine all these.

A scientist might profitably spend a career in just these caves, but Prideaux’s focus is broader. “I look at responses of Australian fauna to past environmental changes, particularly vertebrates of southern and central Australia,” he says. This involves both the environmental changes of the last few million years, and the impact of humans.

Prideaux rejects the “megafauna wars” fought by those who think climate change wiped out most of Australia’s large beasts and those who consider humans responsible. “With the exception of a few individuals, most palaeontologists and associated scientists believe that multiple factors contributed or that we simply lack sufficient data to explain patterns with any certainty,” Prideaux says.

To try to fill the gaps Prideaux uses field sites, such as the Nullarbor caves, that track changes in the composition of local communities and compares them with what we know about climatic shifts. He believes that new technologies will help us solve many important palaeontological questions.

“One thing that has happened over the last decade is improvements in dating,” he says. “Without knowing the time periods fossils are from we will never have a hope of working out why species disappeared.” Among the new techniques are optically stimulated luminescence and methods for pushing radiocarbon dating back to previously unmeasurable eras. “Uranium series methods have advanced a lot,” he adds.

Prideaux says that other advances come from “microwear – tiny pits left in teeth by the kinds of foods animals eat”. The use of micro-CT scans that measure enamel volume is allowing palaeontologists to track changes in dietary adaptations, which in turn relate to climatic and ecological change.

Another development Prideaux points to is the use of stable carbon and oxygen isotopes to see if the plants that an animal was feeding on used the C3 or C4 photosynthesis pathway or whether the climate was relatively wet or arid. This, he says, “provides key insights into the main drivers of the evolution of marsupial herbivores, particularly kangaroos”.

Surprisingly, Prideaux says that “a lot of past estimates of animal body size have been very much arm-waving”. New techniques are changing this, and in the process helping to reveal Australia’s climatic history. “Herbivores tend to grow bigger in arid climates,” Prideaux says. “Diprotodons eat more than wombats, but less per unit mass. Larger body sizes allowed them to thrive on nutrient-poor vegetation.”

With so many exciting developments in the field, it comes as a shock to hear Prideaux say there are probably only a dozen full-time vertebrate palaeontologists in Australia. As a fraction of Australia’s estimated 60,000 practising scientists this is tiny. Prideaux says that “many people still think of palaeontology as all about collecting dinosaur bones and putting them on display in a museums. This might have been true a century ago, but not today.”

Instead Prideaux says the job involves collaborating across numerous fields, from geochronologists who establish the age of bones or sediments to pollen experts and geologists. He sees his role as a jack-of-all trades bringing together multidisciplinary teams to make sense of the bones retrieved on digs.

Jobs in palaeontology may be scarce, but Prideaux believes that “this is exactly the right time to get into palaeontology. The field is reinventing itself. There was a spike in the late 19th century, but in the mid-20th century we were down to one or two people in the country. As part of the higher education revolution there was a boom of jobs in the field, but through the 90s and 2000s a lot of people retired and weren’t replaced.

“Now there is generational change. A lot of things we are looking at – like climate change and how the environment affects species – can be used to better manage the modern situation. There is a wave building as universities, museums and national park agencies recognise the importance of historical perspectives in managing modern biodiversity.”

For young enthusiasts contemplating a career in palaeontology, Prideaux says: “If you’re good enough and motivated you’ll make it.”