Palaeontologists in South Africa have unearthed what may be the oldest burial site in the world, containing remains of a small-brained ancient humans and carved symbols on cave walls, and perhaps forcing a revision of current theories.

Led by renowned palaeoanthropologist Lee Berger, researchers said they discovered several specimens buried about 30 meters (100 feet) underground in a cave system within the Cradle of Humankind, a UNESCO World Heritage site near Johannesburg.

"These are the most ancient interments yet recorded in the hominin record," the scientists wrote in a series of yet to be peer reviewed and preprint papers to be published in eLife.

The findings challenge the current understanding of human evolution, as it is normally held that the development of bigger brains allowed for the performing of complex, "meaning-making" activities such as burying the dead.

The oldest burials previously unearthed, found in the Middle East and Africa, were around 100,000 years old. Those found in South Africa by Berger, whose previous announcements have been controversial, and his fellow researchers, date back to at least 200,000 B.C.

Critically, they also belong to Homo naledi, which had brains about the size of oranges and stood about 1.5 meters (5 feet) tall with curved fingers and toes, tool-wielding hands and feet made for walking.

Homo naledi is named after the "Rising Star" cave system where the first bones were found in 2013.

The oval-shaped interments at the center of the new studies were also found there during excavations started in 2018.

The holes, which researchers say evidence suggests were deliberately dug and then filled in to cover the bodies, contain at least five individuals.

The burial site is not the only sign that Homo naledi was capable of complex emotional and cognitive behavior, the researchers said.

Engravings forming geometrical shapes, including a "rough hashtag figure," were also found on the apparently purposely smoothed surfaces of a cave pillar nearby.