Exclusive: Controversial skeleton may be a new species of early human

More than twenty years after it was first discovered, an analysis of a remarkable skeleton discovered in South Africa has finally been published – and the specimen suggests we may need to add a new species to the family tree of early human ancestors.

The analysis also found evidence that the species was evolving to become better at striding on two legs, helping us to understand when our lineage first became bipedal.

The specimen, nicknamed “Little Foot”, is a type of Australopithecus, the group of hominins to which the famous fossil “Lucy” belonged. Lucy’s species is called A. afarensis, but we know of several other species of these human-like primates living in Africa around 2 million years ago, including A. africanus.

The findings have come out amidst a long-running controversy over who should have access to the fossil. As a result, the team that has been working on the fossil for decades have published their first papers online before peer review was complete, to ensure their work comes out before the studies of a second research group that has been granted access to the specimen.

Discovery of a lifetime

The Little Foot fossil came to light in the 1990s. Ronald Clarke of the University of the Witwatersrand in Johannesburg, South Africa was asked to go through a collection of bones from Sterkfontein Cave in South Africa. In 1994 he found that four foot bones, thought to belong to monkeys, actually resembled existing fossils belonging to the Australopithecus group.

The foot bones were quite small, prompting Clarke’s now-deceased colleague Phillip Tobias to dub them “Little Foot”, in reference to the Bigfoot hominin that some believe roams North America.

In 1997, Clarke and two colleagues found more of the skeleton encased in rock within the same cave. He began excavating it, a process that continued for over a decade. Because the fossilised bone flaked easily, Clarke chose to painstakingly remove the bones from the rock using only an air scribe – a tool that shoots out a thin jet of pressurised air.

“I’ve spent 20 years getting this skeleton, finding it in the rock in the deep darkness of the cave, locating every bone, and then cleaning it sufficiently so we could identify them in the cave, undercutting them, bringing them out in blocks, cleaning them, reconstructing them,” says Clarke.

The result is a virtually complete skeleton that promises to tell us much about early human-like primates.

An elderly lady

A flurry of initial studies, published at last, reveal that Little Foot was an elderly female, about 130 centimetres in height.

According to a study led by Travis Pickering of the University of Wisconsin-Madison, Little Foot had an arm injury. He suspects she fell onto an outstretched hand during her youth, and that the resulting injury troubled her throughout her life.

Robin Crompton of the University of Liverpool, UK and his colleagues have analysed how she would have walked. He says it is the first fossil of this age ever to have been discovered with its limbs fully intact.

“This hominin had longer lower limbs than upper limbs, like ourselves,” says Crompton. This is an interesting finding, as the slightly older hominin Ardipithecus, which came before Australopithecus, had longer arms than legs – more like great apes do. “That means it was being selected for stride length in bipedalism,” says Crompton.

Little Foot would not have been as good at carrying objects as we are. However, she would have been better at climbing trees than modern humans.

That would have suited her home: a mix of tropical rainforest, broken woodland and grassland, through which she roamed widely.

A further paper examines the deposits in which Little Foot was encased and concludes that the fossil is 3.67 million years old, more than a million years older than previously thought.

A “new” species?

Clarke has argued for over a decade that Little Foot does not belong to any of the known Australopithecus species, and should be named a new species in its own right. He favours calling it A. prometheus.

The name was coined in 1948 by Raymond Dart, to describe a piece of skull found at Makapansgat in South Africa. Dart is a key figure in anthropology, because in 1925 he described the first Australopithecus specimen, the Taung Child. He used the fossil to argue that humans evolved in Africa. At the time most biologists thought our origins lay in Asia, and Dart was ridiculed for years until other discoveries confirmed that he was right.

Clarke is convinced that many of the bones from Sterkfontein, including Little Foot, are not A. africanus, so he has resurrected the name A. prometheus. “There are many, many differences, not only in the skull but also in the rest of the skeleton,” he says. They include a flatter face than A. africanus, and larger teeth with a big gap between the upper canines and incisors.

There is also Little Foot’s diet. Based on her teeth, she ate almost nothing but plants. “A. africanus was more omnivorous,” says Clarke.

However, the release of the new data has been overshadowed by an internal dispute at the University of the Witwatersrand.

Race to publish

The dispute arose between Clarke and his colleague Lee Berger, who in recent years has discovered two new species of hominin: Australopithecus sediba and Homo naledi.

Berger’s team had found that H. naledi was unexpectedly young for such a primitive-looking species, the fossils dating to just 250,000 years ago. A. sediba was also anomalous, so they decided the relationships between the various hominin species needed re-examining.

In 2016, they applied to a university committee to ask for a look at Little Foot. “We had been told since at least 2008 that there were publications imminent on Little Foot,” says Berger, so he believed Clarke’s analyses were almost complete.

However, Clarke did not want to give Berger access before his studies were published. “He’s been attempting to take this over from the time I found it,” says Clarke. Berger denies this, and a university inquiry previously found he did nothing untoward regarding Little Foot.

Clarke resisted Berger’s request, but in 2017 the university decided Berger should be given access. However, they specified that Berger could not publish before 30 November 2018, to allow Clarke time to publish his first.

A few days after that deadline, four papers by Clarke’s team, which includes his wife Kathleen Kuman appeared on the preprint site bioRxiv. Three of these studies are intended for a special issue of the Journal of Human Evolution. The fourth – which suggests Little Foot had an arm injury – is being prepared for another journal. None has yet completed peer review. The Journal of Human Evolution has also accepted a further three papers, none of which are online yet.

“For me, the hip joint is confirmatory,” says Crompton, believing that no other known hominin could have walked in the same way as Little Foot.

If A. prometheus is indeed a real, unrecognised species, it would confirm New Scientist’s prediction last December that a new hominin species would be found in 2018. However, most palaeontologists have long disputed its existence.

Berger, with John Hawks of the University of Wisconsin-Madison, has an upcoming paper in the American Journal of Physical Anthropology, which will publish early next week and which the journal shared with New Scientist.

Berger and Hawks argue that the name A. prometheus should not be used because Dart’s initial specimen was not informative enough to identify a new species. Indeed, Dart himself ultimately changed his mind about it. That means, according to taxonomic rules, the name cannot be revived without a formal description of the species.

Little Foot might belong to a new species but it is not possible to judge on what has been published so far, says Hawks. “What I am not seeing in these papers is the data.” He says that now the fossil is available for other researchers to examine, Little Foot will become a crucial fossil.

Berger would not comment on whether he thinks Little Foot belongs to a new species.

References: bioRxiv 10.1101/481556; 10.1101/483495; 10.1101/482711; 10.1101/486076