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Australia's giant extinct marsupials may be ID'd using tiny bone bits
While fictional depictions of fossil discoveries often feature someone finding an entire dinosaur bone in their backyard, the reality of paleontology usually involves puzzling over disparate fragments of a skeleton. Yet despite this often incomplete picture, even a tiny shard of bone can reveal new information—but only if scientists can be sure of exactly which species it belongs to.
So how exactly do scientists determine where such fragments come from? One relatively new method for studying ancient bones is palaeoproteomics, the study of preserved proteins. A study published June 3 in Frontiers in Mammal Science describes the first successful use of this type of technique to characterize the bones of extinct species of Australian marsupial megafauna–the giant ancestors of today's Australian marsupials. The team took successful collagen samples from three such species: Protemnodon mamkurra, a giant kangaroo-like creature that is distantly related to today's kangaroos; Zygomaturus trilobus, a member of the extinct Diprotodontidae family that resembles a colossal wombat the size of a present day hippo; and Palorchestes azael, an unusual herbivore that bears a vague resemblance to a tapir.
[ Related: Giant wombats the size of small cars once roamed Australia. ]
Carli Peters of the Universidade do Algarve's MATRIX Project and one of the paper's co-authors, tells Popular Science that the research involved the use of zooarchaeology by mass spectrometry, or ZooMS.
'ZooMS is … based on small differences in the main bone protein, collagen type I, between species/genera/families,' she says. These differences allow for the identification of a collagen 'fingerprint,' which can then be compared to a sample from an as-yet-unidentified bone. If the fingerprints match, you can conclude that the bones are from the same species.
Study co-author and archaeological scientist Katerina Douka explains that this technique can be used to sort through large numbers of fragments in a way that is impractical for other methods such as DNA sequencing.
'Such screening is not practical using DNA due to library preparation and sequencing costs and computational power needed,' she tells Popular Science
But while collagen is hardy and generally less susceptible to degradation over long timescales than DNA, Australia's harsh environment has nevertheless made finding usable samples difficult.
'Fossils deposited in hot, dry and arid places, such as large parts of Australia, lose their collagen very early…. The major challenge [has been] discovering bones that contain [enough] collagen to allow us to apply such type analyses,' Douka says,
The bones used for the study were found in the country's relatively temperate southeast and were initially used for radiocarbon dating and stable isotope analysis of other specimens. This research revealed the presence of preserved collagen, and the team jumped on the opportunity to study them. As Douka points out, 'This is the first time that such markers [have] become available for Australian megafauna.'
This new data immediately opens doors for new research. 'We could identify these species at sites where they were previously not found, furthering our understanding of the past geographic range of these animals,' says Peters.
[ Related: Super-muscular 374-pound kangaroos once thumped around Australia and New Guinea. ]
However, there remain many, many more species for which no markers currently exist. These include some of the most fascinating and iconic of Australia's megafauna. These include various members of the genus Diprotodon, the largest marsupial genus to have ever existed, and Thylacoleo carnifex, the 'marsupial lion' that emerged roughly 2 million years ago during the late Pleistocene and was the continent's apex predator for millennia.
Like the rest of Australia's megafauna, Thylacoleo carnifex disappeared around 50,000 years ago. Why? No one knows exactly why, and while the leading theory is that humans were to blame–the extinctions of the last megafauna coincide roughly with the arrival of humans in Australia–any new research carries the tantalizing possibility of shedding more light on how these species met their ultimate demise. Douka hopes that new tools like ZooMS might be able to 'help confirm or deny suggestions that early Aboriginals co-existed with megafauna in Australia.'
