Little Foot: The Most Complete Australopithecus Skeleton

Little Foot is the nickname of StW 573, a fossil skeleton of Australopithecus found in the Sterkfontein Caves near Johannesburg, South Africa. Recognised from a few foot bones in 1994 and traced to the cave in 1997, it took Ron Clarke and his team some 20 years to free it from rock. Unveiled in 2017, it is the most complete Australopithecus skeleton yet discovered, and possibly one of the oldest.

Background: the Sterkfontein Caves

Sterkfontein is a limestone cave system about 40 kilometres north-west of Johannesburg. Lime miners blasted its deposits in the early 20th century, and since Robert Broom’s work in the 1930s and 1940s it has produced hundreds of hominin fossils, including the skull known as Mrs Ples. It forms part of the Cradle of Humankind, a UNESCO World Heritage Site since 1999.

The cave’s deposits are divided into numbered layers called members. Little Foot comes from Member 2 in a chamber called the Silberberg Grotto, which is older than the layers that yielded most other Sterkfontein fossils.

Discovery in a museum box

In 1994 the palaeoanthropologist Ron Clarke was sorting through boxes of animal bones collected years earlier from miners’ rubble in the Silberberg Grotto. He identified four small hominin foot bones that fitted together to form part of a left foot. With Phillip Tobias he published them in Science in 1995, noting that the foot combined a human-like heel with a big toe able to grasp. Tobias nicknamed the find Little Foot.

In 1997 Clarke found more bones from the same individual in other boxes, including a broken lower leg bone (tibia). He gave a cast of the broken end to two preparators, Stephen Motsumi and Nkwane Molefe, and sent them into the dark Silberberg Grotto to look for the matching piece. After about two days of searching the rock walls by lamplight, they found it, still embedded in the cave floor.

Twenty years of excavation

The rest of the skeleton lay in hard breccia, a natural concrete of rock fragments and cave sediment. Clarke’s team removed the bones using small hand tools and air scribes, working millimetre by millimetre. The skeleton had partly collapsed, and some parts had been damaged or moved by later rockfalls and the earlier blasting.

The skull was exposed in 1998, but full extraction was not completed until 2012. After further cleaning and reconstruction, the University of the Witwatersrand presented the assembled skeleton to the public on 6 December 2017. A series of detailed scientific papers followed, mostly in 2019.

What the skeleton shows

Little Foot appears to have been an older adult female about 130 centimetres tall. Her legs were adapted to upright walking, while her arms were about as long as her legs and her shoulders were ape-like, suggesting she also climbed trees often. Studies of her inner ear, hands and spine continue to refine this picture of a creature at home both on the ground and in trees.

The position of the skeleton suggests she may have fallen down a shaft into the cave, where her body was later buried by sediment. Her left forearm shows signs of an old injury that had healed during her lifetime, and the wear on her bones and teeth is consistent with an individual who had lived a long life by the standards of her species.

Because so much of one body survives, researchers can measure limb proportions directly instead of combining bones from different individuals, as has often been necessary with other australopithecines. This is one reason the skeleton is so valuable, even beyond the arguments over its age.

The age and species debates

In 2015 Darryl Granger and colleagues used cosmogenic aluminium and beryllium isotopes in quartz to date the surrounding sediments to about 3.67 million years, with an uncertainty of around 160,000 years. That would make Little Foot roughly as old as the Laetoli footprints and older than Lucy.

Other scientists, dating the flowstone layers around the skeleton with uranium-lead methods, obtained ages of about 2.2 to 2.8 million years and argued that the skeleton lay in a pocket of younger sediment. The question is not settled.

The species is also debated. Clarke assigns Little Foot to Australopithecus prometheus, a name Raymond Dart gave to fossils from Makapansgat in 1948 and which most researchers had long merged into A. africanus. Others prefer A. africanus or keep the identification open.

Timeline

• 1994: Ron Clarke identifies four hominin foot bones in boxes from the Silberberg Grotto.
• 1995: Clarke and Tobias publish the foot bones in Science.
• 1997, July: Stephen Motsumi and Nkwane Molefe find the matching tibia in the cave wall.
• 1998: The skull is exposed in the breccia.
• 2012: The last parts of the skeleton are removed from the cave.
• 2015: Cosmogenic dating gives an age of about 3.67 million years.
• 2017, 6 December: The assembled skeleton is unveiled at the University of the Witwatersrand.

Why it matters

Little Foot gives scientists a rare chance to study the whole body of one Australopithecus individual, rather than pieces from many. Whatever its final age and name, it is central to understanding how early hominins in southern Africa walked, climbed and lived.