The fossils of Sterkfontein: Mrs Ples, Little Foot and human origins

From lime mine to fossil site

The story starts with blasting. In 1896 Guglielmo Martinaglia blew his way into the caves to get lime for a fast-growing Johannesburg, and the miners threw fossil-rich rock onto dumps. In 1936, inspired by Raymond Dart's Taung Child, Robert Broom came looking. On 17 August that year the quarry manager handed him the first adult fossil of what is now called Australopithecus africanus. November 2026 marks 90 years since that research began, and Wits is celebrating it.

Mrs Ples

On 18 April 1947 Broom and John Robinson lifted a near-complete skull out of the rock. Catalogued as Sts 5, it got its nickname from Plesianthropus, the name Broom first gave it. Nobody is sure the name fits: some studies read the skull as a middle-aged female, others as an adolescent male. The original is held at the Ditsong National Museum of Natural History in Pretoria. One of Wits's own pages labels Mrs Ples as Sts 14, but Sts 5 is the catalogue number used in scientific publications.

Little Foot

Little Foot was found twice. In 1994 Ronald Clarke was sorting boxes of mixed fossils from a miner's dump in the Silberberg Grotto when he picked out four foot bones of an early hominin. In 1997 Stephen Motsumi and Nkwane Molefe went into the cave with a matching piece of bone and, within two days, found the rest of the skeleton in the rock. It took about 20 years to excavate, clean and reconstruct. Wits calls it the most complete early hominin skeleton yet found, and it was unveiled in 2017.

Why the dates keep moving

Age is the live argument at Sterkfontein, because the caves are hard to date. Older methods put Mrs Ples at about 2.1 to 2.6 million years. A 2022 study that dated the surrounding sediment instead pushed the Australopithecus deposits back to about 3.4 to 3.7 million years, and Wits's research page now says about 3.3 million for Mrs Ples, while another of its pages still says 2.4 million. For Little Foot, estimates have ranged from about 2.2 million to the 3.67 million that Wits uses. If you meet different numbers on your visit, this is why.

Whose species?

Mrs Ples is classed as Australopithecus africanus. Little Foot is harder. Clarke and his colleagues assigned it to Australopithecus prometheus, and Wits's site uses that name, but a 2025 reassessment argues that this name should go and that the fossils belong with africanus. The practical point is that a few well-preserved fossils can reshape the human family tree, and this one is still doing it. Wits's September 2026 newsletter said new Little Foot research was about to be published.

A place on the World Heritage list

UNESCO listed the Fossil Hominid Sites of South Africa in 1999, and Sterkfontein sits at the centre of the area now called the Cradle of Humankind. Wits credits the caves with over 700 hominid specimens. Other sources give lower counts, and you will also read that more than a third of early hominid fossils found before 2010 came from here. Swartkrans nearby, also run by Wits, has given Paranthropus fossils, early Homo and some of the earliest known controlled use of fire. No public tour of it is advertised.

Research you can watch

The work carries on. Current studies on the Wits site include the Member 4 re-dating and a machine-learning study of tooth marks on hominin fossils that points to scavenging by brown hyenas. At the caves, the public-facing preparation laboratory lets you watch technicians and students cleaning and cataloguing fossils. The exhibition next to it holds one of only two full casts of the Little Foot skeleton, and the first complete leg of a Paranthropus, from Swartkrans.

Read next: What to see inside Sterkfontein Caves