About 70 million years ago, a small, hairy platypus-like creature roamed the shores of an ancient lake. It wouldn’t have been a remarkable event, except for one thing: the lake was in present-day Argentina, not Australia.
The creature, nicknamed Patagorhynchus pascuali, is the oldest fossil of the group of egg-laying mammals known as monotremes ever found in South America. The discovery could rewrite the evolutionary history of these quirky early mammals. Today, the five living species of monotremes – which include the platypus (Ornithorhynchus anatinus), the short-beaked echidna (Tachyglosse aculeatus) and three species of long-beaked echidnas (Zaglosse) — are found exclusively in Australia and a few of the surrounding islands. So how did an ancestor of the platypus end up so far from Down Under?
Millions of years ago, Australia, South America and Antarctica (along with parts of Africa and Asia) were united in a supercontinent called Gondwana. This mega landmass began to break apart about 180 million years ago, during the Jurassic period, but did not completely separate until about 66 million years ago, at the end of the Cretaceous.
Because more recent monotreme fossils have been discovered in South America, scientists have previously speculated that the group evolved on the Australian landmass after this continental break and then migrated to South America via a bridge. earthly. But the fact that P. pascuali existed in Argentina before the breakup of the continent tells a different story.
“Our finding clearly demonstrates that monotremes evolved not just on the Australian mainland, but also in other parts of southern Gondwana,” study co-author Fernando Novas (opens in a new tab)a paleontologist from the Bernardino Rivadavia Museum of Natural Sciences in Buenos Aires, Argentina, told Live Science in an email.
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The specimen, which was described in the journal Communications Biology (opens in a new tab) on February 16, was identified by a lower jaw fragment containing a molar. When it comes to studying the fossilized remains of mammals, “the teeth give us an enormous amount of information”, Robin Beck (opens in a new tab), an evolutionary biologist at the University of Salford in the UK who was not involved in the study, told Live Science in an email. In the case of monotremes, however, dental identification is somewhat more complicated.
“Living platypus lack teeth,” Novas said. But another extinct relative of the platypus, the one 30 million years old Obdurodon, preserved teeth in its upper and lower jaws. THE P. pascuali molar closely resembled these teeth, as well as the very small imperfect teeth that baby platypuses briefly possess.
From its teeth and apparent habitat, P. pascuali probably had a diet similar to that of a modern platypus: mostly small aquatic invertebrates, including insect larvae and snails. The Argentinian fossil bed where it was discovered confirms this; Novas said he found insects and snail shells in the sediment around P. pascuali. Additionally, researchers have discovered the fossilized remains of other early mammals, turtles, frogs, snakes, aquatic plants, and a variety of dinosaurs.
While the discovery is an important and interesting new piece of the monotreme evolutionary puzzle, researchers are still a long way from having the complete picture. “There are still huge gaps in the monotreme fossil record,” Beck said. For example, although no monotreme fossils have been found in Antarctica, given its earlier proximity to Australia and South America, there are likely ancient platypus bones deep under the ice.
But as a South American paleontologist, Novas, says, it’s pretty cool to know that “the Australian’s great-grandfather Ornithorhynchus was Argentinian.”