Echidnapus identified from an 'Age of Monotre

Published today in the Alcheringa: an Australasian journal of paleontology, evidence of a “monotreme age” has been discovered by a team of Australian scientists from the Australian Museum (AM), Museums Victoria and the Australian Opal Centre.

The discoveries were led by two renowned mammals, Australian Museum Honorary Associate Professor Tim Flannery; and Professor Kris Helgen, Chief Scientist and Director of the Australian Museum Research Institute (AMRI).

Found in the Lightning Ridge opal fields of New South Wales, the opalized jaws date back to the Cenomanian age of the Cretaceous, between 102 million and 96.6 million years ago.

Professor Flannery said the research reveals that 100 million years ago Australia was home to a diversity of monotremes, of which the platypus and echidna are the only surviving descendants.

“Today, Australia is known as a land of marsupials, but the discovery of these new fossils is the first indication that Australia previously supported a diversity of monotremes. It’s like discovering a whole new civilization,” Professor Flannery said.

Professor Kris Helgen, chief scientist and director of the Australian Museum Research Institute, said the three new species exhibit combinations of features never before seen in other living or fossil monotremes. One of the most striking new monotremes, Opalios splendensretains characteristics of the first known monotremes, but also some that foreshadow adaptations in living monotremes, echidnas and platypuses.

“Opalios splendens is in a place in the evolutionary tree before the evolution of the common ancestor of monotremes that we have today. Its general anatomy is probably very similar to that of the platypus, but with jaw and snout features a bit more echidna-like – one might call it an 'echidnapus',” Professor Helgen said. .

“The evolutionary history of our egg-laying mammals goes from “toothed to toothless” on the oldest monotreme, Teinolophos trusleri, which dates back to Victoria 130 million years ago. What we see at Lightning Ridge is that 100 million years ago, some monotremes still had five molars, but some only had three,” Professor Helgen said.

Professor Flannery pointed out that today, echidnas have no teeth and platypus too are essentially toothless.

“Adult platypus have no teeth, although juveniles have rudimentary molars. When and why adult platypuses lost their teeth after nearly 100 million years is a mystery we think we've solved. It may have been competition with the Australian water rat, which arrived in Australia within the last two million years, that caused the platypus to seek softer, slipperier foods better processed with the pads tough ones that adults use today,” Professor Flannery said.

“What's so unusual about this quintessentially Australian story is that in one snapshot we see six different egg-laying mammals living together at Lightning Ridge over 100 million years ago. All hold potential evolutionary destinies that may go in different directions, and all are very distant ancestors and relatives of current living monotremes.

Dr Matthew McCurry, curator of palaeontology at the Australian Museum, said the discovery of three new genera of monotremes helps piece together their remarkable evolutionary history.

“There are six species of monotremes, including the three newly described here, within the Cenomanian Fauna of Lightning Ridge of New South Wales, making this the most diverse assemblage of monotremes ever recorded. Four species are known from a single specimen, suggesting that diversity remains underrepresented. This discovery adds more than 20 percent to the previously known diversity of monotremes,” said Dr McCurry.

“We have very few monotreme fossils, so discovering new fossils can tell us more about where they lived, what they looked like, and how environmental changes influenced their evolution. Every important monotreme fossil currently known is part of this evolutionary history, since Teinolophosthe small shrew-like creature that lived in Antarctica from 130 million years ago to the present day,” Dr McCurry said.

Museums Victoria Research Institute co-authors Dr Thomas Rich, Senior Curator of Vertebrate Palaeontology, and Honorary Associate Professor Patricia Vickers-Rich AO, said these curious, unique and ancient Australian animals still have the power to interest the scientific world.

“The platypus and echidna are iconic Australian species. The discovery of several new species in a small area suggests that the family tree of egg-laying monotremes is far more complicated than living platypuses and echidnas alone would suggest,” said Dr. Thomas Rich.

“As fieldwork continues in the Australian Mesozoic, we continue to better understand how life changed over time. For me, this is what makes science so exciting,” said Professor Patricia Vickers-Rich AO.

The fossils were found by Elizabeth Smith and her daughter Clytie of the Australian Opal Center at Lightning Ridge, who spent decades working and researching the opal fields.

“Opal fossils are rare, but opalized monotreme fossils are infinitely rarer, because there is one monotreme fragment for every million other pieces. We don’t know when or where exactly they will appear,” Elizabeth Smith said.

“These specimens are a revelation. They are showing the world that long before Australia became the land of pouched mammals, marsupials, it was a land of fur layers – monotremes. It appears that 100 million years ago there were more monotremes at Lightning Ridge than anywhere else on earth, past or present,” Elizabeth said.