Fossil analysis reveals three ancient species of egg-laying mammals

Scientists sometimes make discoveries by rummaging through museum drawers. A recent analysis of fossils discovered in an opal mine in Lightning Ridge, a village in New South Wales (southeastern Australia), preserved for decades in the collections of the Australian Museum in Sydney, led to the discovery of six now extinct species of monotremes, mammals that lay eggs and nurse their young. Three of them were completely unknown to date.

At least that’s what Tim Flannery and his colleagues assure us. Paleontologists describe their discovery in a study published in Alcheringa: An Australasian Journal of Palaeontology on May 26. At the time these animals lived, 100 million years ago, dinosaurs dominated the planet, Australia was part of the supercontinent called Gondwana, and Lightning Ridge was a tropical, swampy area.

“Among these new species identified, Opalios splendens shares characteristics with both echidnas and platypus, earning it the nickname ‘echidnorynpus’. It was classified in the new family Opalionidae. precise New Scientist. Despite the similarities between this creature and platypus and echidnas, researchers are unable to say whether it is a common ancestor of these two monotreme species.

They lived before marsupials

Indeed, genetic analyzes suggest that the group of platypuses and that of echidnas diverged around 50 million years ago. However, the new family Opalionidae lived well before. It is possible that it had already completely disappeared when the direct ancestor of current species began to emerge.

Aidan Couzens, a paleontologist at Flinders University in Adelaide, who was not involved in the work, believes that this study puts forward several interesting scenarios. “So monotremes could have dominated the mammal fauna of Australia during the age of the dinosaurs, before being later ousted by marsupials, he says in the British magazine. But we will need other fossils, better preserved, and ideally from other sites to examine the veracity of these fascinating hypotheses.”