An ancient platypus-like fossil could rewrite the history of egg-laying mammals

An artist’s illustration of what Patagorhynchus pascuali probably looked like in life. (Image credit: Courtesy of Fernando Novas)

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.

A reconstruction of Patagorhynchus pascuali‘s skull, with the fossilized molar. (Image credit: Courtesy of Fernando Novas)

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.

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