A new species of ancient human, thought to have been under 4ft tall and adapted to climbing trees, has been discovered in the Philippines, providing a twist in the story of human evolution.

The specimen, named Homo luzonensis, was excavated from Callao cave on Luzon island in the northern Philippines and has been dated to 50,000-67,000 years ago – when modern humans and the Neanderthals were spreading across Europe and into Asia.

Florent Détroit, of the Natural History Museum in Paris and the paper’s first author, said the discovery provided the latest challenge to the fairly straightforward prevalent narrative of human evolution.

It was once thought that no humans left Africa until about 1.5 million years ago, when a large-bodied ancient human called Homo erectus set off on a dispersal that ultimately allowed it to occupy territory spanning Africa and Spain, China and Indonesia.

Then, according to the traditional narrative, after a few hundred-thousand years of not much happening, our own ancestors dispersed from Africa about 50,000 years ago.

“We now know that it was a much more complex evolutionary history, with several distinct species contemporaneous with Homo sapiens, interbreeding events, extinctions,” said Détroit. “Homo luzonensis is one of those species and we will [increasingly see] that a few thousand years back in time, Homo sapiens was definitely not alone on Earth.”

Facebook Twitter Pinterest Some of the teeth that were found belonging to Homo luzonensis. Photograph: Callao Cave Archaeology Project

The excavation did not yield a complete skeleton: seven teeth, two hand bones, three foot bones and one thigh bone were found, thought to belong to two adults and one child. Nevertheless, the fossils provide intriguing clues to the appearance and lifestyle of Homo luzonensis.

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The tiny teeth suggest the human would have been shorter than 4ft tall – possibly even shorter than another ancient species, Homo floresiensis, sometimes called the “hobbit”, also found in south-east Asia and dating to about the same period. Most intriguing was the presence of a curved toe bone, which closely resembled the anatomy of far more ancient species such as Australopithecus, known only in Africa and dating to 2m-3m years ago.

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Normally this anatomy would indicate a mixed lifestyle with an ability to walk on two legs and climb trees. One possibility is that this primitive trait reappeared once the species had become isolated on the island. “Maybe the way they were walking was distinct,” said Détroit. “This is something we plan to work on in the near future.”

It is not known whether the new species, along with the ‘hobbit’, represent earlier dispersals from Africa than Homo erectus, or whether they are descendants who later shrank and evolved new anatomical traits.

Facebook Twitter Pinterest The Homo floresiensis ‘hobbit’ skull compared with a modern human skull. Photograph: Yousuke Kaifu

Another mystery is how they arrived at Luzon, a large island that has never been connected to the mainland by a land bridge. One possibility is that the early humans set out to sea intentionally on some form of raft; another is that they were washed there in relatively large numbers due to a natural event such as a tsunami.

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“Arrival by accident … is favoured by many scholars, but this is mainly because of arguments like ‘Homo erectus were not clever enough to cross the sea on purpose’,” said Détroit. “But the fact is that we have now more and more evidence that they successfully settled on several islands in the remote past in south-east Asia, so it was probably not so accidental.”

Chris Stringer, head of human origins research at the Natural History Museum in London, who was not involved in the find, said another crucial question is what caused the demise of these early humans and whether our own ancestors played a role.

“As for the fate of luzonensis, it is too early to say whether the spread of Homo sapiens into the region at least 50,000 years ago might have been a factor in its disappearance,” he said.

The findings were published in the journal Nature.

• This article was amended on 18 April 2019 to correct a reference to “our own ancestors” to that of “modern humans”.