How did tortoises reach the Galápagos Islands? © Getty Images

How did tortoises reach the Galápagos Islands?

Asked by: Tamsin Nicholson

The Galápagos tortoises are iconic animals, often living for over 100 years and weighing as much as 400kg. They’re only found on the Galápagos Islands in the Pacific Ocean, nearly 1,000km away from the nearest landmass, Ecuador. So scientists have long scratched their heads over how they got there in the first place.

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In the early 19th Century, some thought that sailors had transferred the giant tortoises to the Galápagos Islands from the Mascarene Islands in the Indian Ocean. However, thanks to DNA tests, we now know that the ancestor of Galápagos tortoises came from South America.

In the late 1800s, palaeontologist Georg Baur thought that the animals must have walked across an ancient land bridge. They couldn’t have crossed an ocean, he reasoned, because tortoises were thought to be poor swimmers. But then, in 1923, naturalist William Beebe tossed one over the side of a yacht! Fortunately, the reptile was a skilful swimmer, steering itself purposefully and extending its neck upwards to breathe. But a week after the ordeal, it died. Beebe assumed that it had ingested too much seawater, so he found the idea of a tortoise swimming from Ecuador to the Galápagos just too much to swallow.

In the end, it took two lines of evidence to seal the deal for #TeamSwim. In the mid-20th Century, research on plate tectonics confirmed that the Galápagos Islands were formed by volcanic activity. The islands rose from the ocean. There never was a land bridge. And in 2004, a giant tortoise from Aldabra, in the Indian Ocean, walked onto a beach in Tanzania, Africa, after swimming (and/or drifting) for 750km. It was emaciated and covered in barnacles, but otherwise okay.

Scientists now think that Galápagos tortoises became established after a pregnant female ancestor or breeding pair made a similar long-distance swim from South America to the islands, around two million years ago.

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