A year and a half after fossils belonging to the Homo naledi species were discovered, scientists and researchers can now reveal that it is highly likely that the species lived alongside Homo sapiens (early humans).
Speaking at the Cradle of Humankind on Monday ahead of the official announcement, Wits paleoanthropologist Professor Lee Berger, who led the team, said they discovered that the age of the Homo naledi was "startlingly young".
"Homo naledi was alive sometime between 335 000 and 236 000 years ago. This places this population of primitive small-brained hominis at a time and place that is likely alongside Homo sapiens.
"This is the first time that it has been demonstrated that another species of homonin survived alongside the first humans in Africa," Berger said.
Although the Homo naledi fossils shared some primitive features with some of the earliest known members of the Homo genus who lived nearly 2 million years ago, the remains also shared some features with modern humans, he said.
"After the description of the new species in 2015, experts had predicted that the fossils should be around the age of these other primitive species. Instead, the fossils... are barely more than one-tenth that age," Berger said.
Late Middle Pleistocene
The dates were determined through six independent methods by at least 19 scientists from laboratories and institutions across the world.
This meant that Homo naledi may have survived for as long as two million years alongside other species of hominins in Africa, the period which paleoanthropologists like Berger describe as the 'late Middle Pleistocene'.
Researchers and scientists had previously thought that only Homo sapiens existed on the African continent during that period because the period was characterised by the rise of "modern human behaviour".
That kind of behaviour was previously attributed to the rise of modern humans and was thought to represent the origins of complex modern human activities such as burial of the dead, self-adornment and complex tools.
"We can no longer assume that we know which species made which tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioural breakthroughs in the archaeological record of Africa.
"If there is one other species out there that shared the word 'modern humans' in Africa, it is very likely there are others. We just need to find them," Berger said.
More surprises to come
Berger said this recent discovery proved that human evolution and the record of hominin fossils would have more surprises to come.
One of these surprises was the discovery of two adult individuals and one infant with features very similar to those of Homo naledi's in a completely separate chamber called Lesedi.
"The chamber is more than a hundred metres from the Dinaledi chamber. It is almost difficult to access and also contains spectacular fossils of naledi including a partial skeleton with a wonderfully complete skull," University of Wisconsin-Madison Professor John Hawks said.
Remains from the Lesedi Chamber were initially discovered in 2013 however it took about three years to find fuller sets of fossils to work with.
Dr Marina Eliot, who was one of the members of the team which excavated the first Homo Naledi remains in 2015 said getting access to the Lesedi Chamber was only "slightly" easier than the Dinaledi excavation.
"After passing through a squeeze of about 25 centimetres, you have to descend along vertical shafts reaching the chamber. While slightly easier to get to, the Lesedi Chamber is, if anything, more difficult to work due to the tight spaces involved."
Disposing of their dead
This added to the theory that the Homo naledi species were intelligent enough to dispose of their dead, a theory initially raised by the team back in September 2015 during the initial discovery. Although some have criticised it, those directly involved in the process still consider it to be telling.
"What are the odds of a second, almost identical occurrence happening by chance?" Geology lecturer at the James Cook University in Australia Hanna Hilbert-Wolf said.
More than 130 hominin specimens were discovered in the Lesedi chamber, including one of the most complete skeletons ever discovered in the world.
University of Zurich's Professor Peter Schmid, who led the reconstruction of the fossils, said the discovery of the remains was exciting because for the first time, the preserved nature of the fossils including the skull, gave them a better picture of how Homo naledi actually looked.
"We finally get a look at the face of Homo naledi," Schmid said.
The male skeleton has been dubbed 'Neo' which means 'gift' in seTswana and is more complete than one of the most famous fossils ever discovered on the continent, Lucy - a female Austrolopethicus species discovered in Ethiopia in 1974 which is believed to be around 3.2 million years old.
Although the remains belonging to Neo and others in the Lesedi chamber are yet to be dated, Eliott suspects that they may resemble a similar age to those of the original Homo Naledi remains.
Hawks, who co-authored a paper on the discovery of the new fossils titled 'New fossil remains of Homo naledi from the Lesedi Chamber' agreed with Elliott.
"There is no doubt that they belong to the same species," he said.
A team of 52 scientists from 35 departments across the world were involved in researching both the age of the original Homo naledi fossils as well as the newly discovered remains.
Both sets of fossils will be put on display for the public at the Cradle of Humankind in Maropeng from May 25.