About 100m years ago, in what is now an Australian opal field, a strange, hairy, egg-laying, hare-sized mammal slithered through a water hole across a massive polar floodplain.
This mammal – Opalius splendens but what scientists happily blessed with the nickname “echidnapus” – was one of the ancient descendants of one of the planet’s most unique animal orders, the monotremes.
New scientific research released Monday showed the echidnapus has characteristics of the last two remaining members of their tribe.
Modern Australia is the stronghold of the only monotreme species – the extremely strange platypus, a nippleless Aussie mammal with a duck-like bill, and the spiny echidna with its overstretched snout, which also lives in New Guinea.
But the discovery of echidnapus and two more ancient monotremes in the Opal Field fossils means that at least six monotreme species existed in what is now the far north New South Wales abroad.
“It’s like discovering a whole new civilization,” says Prof Tim Flannery, the lead author of the new research, published in paleontology journal Alcheringa.
“Today, Australia is known as the land of marsupials, but the discovery of these new fossils is the first indication that Australia was once home to a diversity of monotremes.
In the region where the fossils were found, “there are no other types of mammals. This suggests that Australia experienced an age of monotremes when they were the dominant mammal.”
The discovery of the opalized jawbones in an area known as Lightning Ridge almost never happened. Elizabeth Smith, of the Australian Opal Centre, and her daughter Clytie found the specimens about 25 years ago while going through the tailings pile of an opal mine.
“It was largely luck that I found the pieces,” she said. “But I immediately knew it was a mammal and therefore very significant.”
She donated the specimens to the Australian Museum around the turn of the millennium. Her finds and those sent to her by opal miners remain at the non-profit opal center these days.
“These samples are a revelation,” she said. “It’s hugely exciting. They show the world that long before Australia became the land of mailed mammals, marsupials, it was a land of furry egg-layers – monotremes.”
The three species are described in the journal from opalized jaws dating back to an age of the Cretaceous between 102m and 96.6m years ago.
A second new ancient monotreme, Parvopalus clytiei, was a small terrestrial mammal. A third, Dharragarra auroralooked “remarkably like a modern platypus,” Flannery said.
Prof Kris Helgen, director of the Australian Museum Research Institute, said Opalios splendens had characteristics of the earliest known monotremes, but other features that pointed to the modern echidna and platypus.
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He said: “Its overall anatomy is probably quite like the platypus, but with features of the jaw and snout a bit more like an echidna – you could call it an ‘echidnapus’.”
Echidnapus could not have been the immediate ancestor because it was too old, Flannery said. But it had a narrow beak like an echidna and five molars like a modern platypus.
One curiosity of the modern platypus—an animal so strange that 18th-century British scientist George Shaw thought it was a potential hoax—is how it lost its teeth (juveniles lose their molars as they mature).
“It’s a mystery we think we may have solved,” Flannery said. About two million years ago, the Australian water rat – known as the rakali – arrived in Australia.
This, Flannery said, likely caused the platypus to seek out “softer, smoother food that is best processed with the leathery pads that adults use today.”
He said all six of Lightning Ridge’s monotremes “hold potential evolutionary fates” that could have branched off in all sorts of directions but were “deeply ancestral and related to the current living monotremes”.
But sometime between 100m and 54m years ago, the monotreme diversity disappeared. “Was it because of the asteroid that killed the dinosaurs? Did they come into competition with the marsupials? We don’t know, but there has been change.”
Dr Matthew McCurry, curator of palaeontology at the Australian Museum, said: “We have very few monotreme fossils, so finding new fossils can tell us more about where they lived, what they looked like and how the environment changed. influenced their evolution.
“Every significant monotreme fossil currently known fits into this evolutionary story, from Teinolophos, the small shrew-like creature in Antarctica 130m years ago, to the present day.”
