OBDURODON life reconstruction
Australia’s platypus, one of the world’s most enigmatic animals, had an exotic origin story, according to an exciting discovery by Flinders University palaeontologists.
They have described rare 25-million-year-old fossils found east of the Flinders Ranges in remote outback South Australia which show an ancient platypus with well-formed teeth. It was able to munch on a varied diet in large inland lakes and rivers, probably with other animals such as ancient lungfish, flamingo and freshwater dolphins.
“Platypuses are extremely rare in the fossil record and are often restricted to teeth, so it’s exciting find new material and learn more about these unique mammals” says Dr Aaron Camens, an author of a new paper in Australian Zoologist, which adds to the long evolutionary history of modern platypuses in Australia.
The well-preserved fossils of the oldest known species, Obdurodon insignis, show that a toothed ancestor of the modern platypus lived during the late Oligocene about 25 million years ago in extensive permanent lakes, slow-flowing rivers and forested lowlands of central Australia.
Obdurodon insignis mainly differs from modern platypus by having well-formed teeth — molars and premolars. The modern platypus has vestigial teeth on hatching but soon loses them and only has small horny pads to chew its food with when adult.
Previously, this ancient platypus was known only by one and a half molar teeth, a jaw fragment and a pelvis fragment.
However, one of the few well-preserved platypus fossils, of a closely related younger (17–14 million years old) species called Obdurodon dicksoni, gave some clues. Found in the Riversleigh World Heritage Area in northwest Queensland, its skull was similar but slightly bigger than modern platypus. It had teeth and a stronger bite.
“The new material includes the first premolar, an important tooth in front of the molars,” says Dr Camens, from the College of Science and Engineering. “This shows Obdurodon insignis had large pointed front teeth which, with its large robust molar teeth, could easily have crushed animals with shells or exoskeletons like yabbies.”
Coauthor Associate Professor Trevor Worthy, also from the Flinders Palaeontology Lab, says the other rare find was the discovery of a partial scapulocoracoid, or bone that supports the arm or front limb.
“This reveals a very similar forelimb structure to modern platypus, indicating it could swim just as well as its modern descendant,” says Associate Professor Worthy.
“These fossils show that 25 million years ago Obdurodon insignis was very similar to the modern platypus. It differed mainly by being slightly larger and having teeth.”
For more than 20 years, the Flinders University team has organised expeditions to an outback desert location east of the Flinders Ranges to studying rocks containing fossils. As the rocks erode and sand shifts, more evidence emerges from evolutionary past of this ‘lost world’.
Among millions of fish bones, more than 1000 fossils of non-fish vertebrate animals have been collected. These include just three fossils of the toothed platypus.
Associate Professor Trevor Worthy and colleagues have studied this lost ecosystem for many years.
“It is for exquisite fossils like these that I return again and again to the desert. One never knows what erosion or one’s efforts will reveal next.”
It’s understood the forests of 25 million years ago supported diverse communities of arboreal or tree-dwelling mammals, such as koalas and many types of possums. Below, on the ground, sheep-sized marsupials browsed, with many other animals at their feet. These included familiar-looking skinks, frogs and small carnivorous marsupials. In the trees, lived numerous birds including the previously described giant eagle Archaehierax.
According to previous discoveries, the lake supported many kinds of lungfish and other smaller fish. Feeding on the fish, or plants and small invertebrates in the lake or along its shores, were several species of waterfowl, cormorants and flamingos.
Little known, is that a small dolphin also lived in these freshwater ecosystems. Its teeth and bones also have been found at several places where the rocks expose this ancient community.
“This is the setting that the ancient, toothed platypus lived in before its bones settled to the floor of the lake 25 million years ago,” says another author Gen Conway, who has created a life reconstruction of the lost aquatic world.
The article, New material of the toothed platypus Obdurodon insignis (Monotremata: Ornithorhynchidae) from the late Oligocene Pinpa Local Fauna at Billeroo Creek, South Australia (2026) by TH Worthy, GA Conway and AB Camens and has been published in international peer-reviewed palaeo-biology journal Australian Zoologist DOI: https://doi.org/10.1071/
Acknowledgements: This study received funding from Flinders University and the Mark Mitchell Foundation.
The authors thank the owners and managers of Frome Downs Station that allowed access to the fossil sites where the fossils were found. Andrew Black (‘Blackie’), and lately, Gavin Johnson and Ben Brinkworth (Willoway Farming) have supported us. Numerous people helped in excavations over the years.
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