Ancient platypus-like fossil could rewrite history of egg-laying mammals

An artistic representation of what Patagorhynchus pascuali probably looked like in real life. (Image credit: Courtesy of Fernando Novas)

About 70 million years ago, a small, furry, platypus-like creature shuffled along the shore of an ancient lake. This would not have been a notable incident, except for one thing: the lake was in present-day Argentina, not Australia.

The creature named Patagorhynchus pascuali, is the oldest fossil of the egg-laying group of mammals known as monotremes ever discovered in South America. The discovery could rewrite the history of where these strange early mammals evolved. Today, all five species are living monotremes – including the platypus (Ornithorhynchus anatinus), the short-beaked hedgehog (Tachyglossus aculeatus) and three species of long-billed echidnas (Zaglossus) – only found in Australia and some of the surrounding islands. So how did a platypus ancestor end up so far from Down Under?

Millions of years ago, Australia, South America, and Antarctica (as well as parts of Africa and Asia) were compressed into a supercontinent called Gondwana. This vast landmass began breaking up about 180 million years ago during the Jurassic period, but only fully separated about 66 million years ago at the end of the Cretaceous period.

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

Since more recent cloaca fossils have been found in South America, scientists previously speculated that the group evolved on the Australian landmass after this continent’s collapse and later migrated back to South America via a land bridge. But the fact that P.pascuali existed in Argentina before the continent’s collapse tells a different story.

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