The fossilised remains of an ancient egg-laying mammal discovered 25 years ago in Australia have been identified by scientists as the oldest known platypus and a new species.
Officially named Opalios splendens, the species has been dubbed 'echidnapus' after its resemblance to the platypus and echidna – the only two monotremes (egg-laying mammals) that live today.
The scientists also found evidence of several other ancient and now extinct monotreme species.
"It’s like discovering a whole new civilisation,” says Professor Tim Flannery, lead author of the study, which was published in Alcheringa: An Australasian Journal of Palaeontology.
Finding echidnapus
The fossils – which date to the Cenomanian Age of the Cretaceous Period, between 102 million to 96.6 million years ago – were found a quarter of a century ago by palaeontologist Elizabeth Smith and her daughter Clytie in the Lightning Ridge opal fields in New South Wales.
Smith donated the specimens to the Australian Museum, where they sat in a drawer until about two years ago when Professor Flannery and his colleague Professor Kris Helgen (Chief Scientist and Director of the Australian Museum Research Institute) found them.
Some of the remains belonged to Steropodon galmani, an ancestor of the platypus already known to science. However, the other fossils were unfamiliar and lead to the discovery of three previously unknown species.
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“Discovering these new fossils is the first indication that Australia was previously home to a diversity of monotremes," says Flannery.
Opalios splendens, or echidnapus, was one of the most striking of the new monotremes identified, says Professor Helgen.
“Opalios splendens sits on a place in the evolutionary tree prior to the evolution of the common ancestor of the monotremes we have today. Its overall anatomy is probably quite like the platypus, but with features of the jaw and snout a bit more like an echidna – you might call it an ‘echidnapus’,” explains Professor Helgen.
Professor Flannery adds that echidnas that live today have no teeth, while platypuses are toothless. “Adult platypus have no teeth, though juveniles have rudimentary molars. Just when and why adult platypus lost their teeth after nearly 100 million years is a mystery we think we have solved. It may have been competition with the Australian water rat, which arrived in Australia within the last 2 million years, which caused platypus to seek out softer, slipperier food best processed with the leathery pads that adults use today.
“What is so unusual about this uniquely Australian story is that in one snapshot we see six different egg-laying mammals living together in Lightning Ridge over 100 million years ago.
"All of them are holding potential evolutionary destinies that can go off in different directions, and all of them are deep distant ancestors and relatives of the current living monotremes.”
Smith, who discovered the fossils 25 years ago, says “opal fossils are rare, but opalised monotreme fossils are infinitely more rare, as there’s one monotreme fragment to a million other pieces. We don’t know when, or exactly where, they’ll turn up.
“These specimens are a revelation. They show the world that long before Australia became the land of pouched mammals, marsupials, this was a land of furry egg-layers – monotremes. It seems that 100 million years ago, there were more monotremes at Lightning Ridge than anywhere else on earth, past or present."
