by Some time about 100m years ago in what is now the Australian opal field, a strange, furry, egg-laying, rabbit-sized mammal slithered through a water hole across a giant polar floodplain.
this mammal – Opalius splendens but gratefully blessed with the nickname “echidnapus” by scientists – it was among the ancient descendants of one of the world’s most unique animal orders, the monotremes.
New scientific research released on Monday revealed that the echidnapus had characteristics of the last two members of their tribe.
Modern Australia is home to the only monotreme species – the extremely strange platypus, a nipple-free Aussie mammal with a duck-like bill, and the spiky echidna with its over-extended snout, which live on New Guinea too.
But the discovery of an echidnapus and two more ancient monotremes in the fossils of the opal field means that there were at least six species of monotremes in what is now southern New South Wales far north.
“It’s like discovering a whole new civilization,” said Professor Tim Flannery, lead author of the new research, published in the palaeontology journal Alcheringa.
“Today Australia is known as the land of marsupials, but the discovery of these new fossils is the first indication that Australia once had a variety of monotremes.
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In the region where the fossils were found, “there is no other type of mammal. It suggests that Australia had an age of monotremes when they were the dominant mammal.”
The opalised jawbones in an area known as Lightning Ridge have never been found. Elizabeth Smith, from the Australian Opal Centre, and her daughter Clytie found the specimens about 25 years ago while going through the tailings in an opal mine.
“I was very lucky to find the pieces,” she said. “But I knew immediately that it was a mammal and therefore very significant.”
She donated the specimens to the Australian Museum around the turn of the millennium. These days her discoveries and those sent to her by opal miners remain at the non-profit opal center.
“These specimens are a revelation,” she said. “It’s really exciting. They show the world that long before Australia became a land of pouched mammals, marsupials, this was a land of furry egg layers – monotremes.”
The three species are described in the journal from opalised jaws dating back to the Cretaceous age between 102m and 96.6m years ago.
The second new ancient monotreme, Parvopalus clytiei, was a tiny land mammal. a third, Aurora Darragarralooks “remarkably like a modern platypus,” Flannery said.
Professor Kris Helgen, director of the Australian Museum Research Institute, said Opalios splendens the characteristics of the earliest known monotremes but other features referring to the modern echidna and platypus.
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He said: “Its overall anatomy is probably platypus-like but with jaw features and a slightly more echidna-like snout – you could call it an ‘echidnapus’.”
Echidnapus could not be an immediate ancestor because it was too old, Flannery said. But it had a slender beak like an echidna and five molars like a modern platypus.
One curiosity about the modern platypus – an animal so strange that 18th-century British scientist George Shaw thought it might be a hoax – is how it lost its teeth (juveniles lose their molars as adults).
“It’s a mystery we think we’ve solved,” Flannery said. About two million years ago, the Australian water rat – known as the rakali – arrived in Australia.
This, Flannery said, was likely due to the platypus seeking “softer, more slippery food that is best processed with the leathery pads that adults use today.”
He said that all six of the Lightning Ridge monotremes have “potential evolutionary destinies” that could split in all directions, but that the current living monotremes are “deeply distant ancestors and relatives”. .
But sometime between 100m and 54m years ago, the monotreme variety disappeared. “Was it the result of an asteroid that killed the dinosaurs? Did they come into competition with the marsupials? We don’t know, but there was a change.”
Dr Matthew McCurry, curator of paleontology at the Australian Museum, said: “We have very few monolithic fossils, so new fossils can tell us more about where they lived, what they were like and how whose evolution was affected by changes in the environment.
“Every significant monotreme fossil currently known represents this evolutionary story, from Teinolophos, the tiny blind-like creature in Antarctica 130m years ago, to the present day.”
