The Homo naledi hominin species, first described in 2015, has been found to have coexisted in subequatorial Africa with other hominin species and was likely present in the same general region as the Homo sapiens species – the direct ancestors of modern humans – scientists say.
The age of the Homo naledi fossils discovered in the Dinaledi chamber of the Rising Star cave system, in the Cradle of Humankind, in Gauteng, were determined to be between 335 000 years and 236 000 years old, University of the Witwatersrand (Wits) paleoanthropologist Professor Lee Berger says.
The significance of the age of these Homo naledi fossils, which are a so-called ‘deep-time’ species of hominins – meaning they share many morphological traits with early hominin species, including teeth, such as large molars, and femur structure similar to the Homo erectus, Homo habilis and Australopithecine species – is that it can be postulated that the species survived until relatively recently in the Cradle of Humankind and provides evidence of the coexistence of hominin species in Africa.
Professor John Hawks of the University of Wisconsin-Madison explains that the Omo Kibish remains from Ethiopia – identified as the earliest fossil evidence of anatomically modern humans – have been determined to be 190 000 years old.
“[Anatomically], modern humans were here in the subequatorial regions of Africa at the same time as Homo naledi, meaning that our relative and distant relative species were here throughout the 2-million to 1.5-million years of our evolution. We must also rethink the diversity of other hominins that existed with each other throughout our evolution.”
A new and remarkably complete fossil of Homo naledi, called Neo – ‘gift’ in Sotho – was discovered in a new chamber, the Lesedi – or light – chamber of the Rising Star cave system.
“The Neo fossil is one of the best represented and best dated fossils in the hominin record and we have to ask serious questions about which hominin species are responsible for the archaeological sites in this area and how the hominin populations’ interactions [played a] role in our own origins.”
The discovery of the Neo fossil is significant because it represents the best understood sample of hominins outside of Neanderthals and modern humans, says Hawks.
Except for a lower leg and the feet that are missing, the Neo fossil is extraordinarily complete and well preserved and includes one of the most complete craniums ever, with the delicate nasal bones, inner eye orbit bones and the tear ducts preserved.
“It is a remarkable view of the past and [a remarkable] realisation that the species was here and we are looking at the face of a hominin relative that our direct ancestors lived alongside,” he enthuses.
Parts of a juvenile’s mandible with a developing tooth embedded inside and a partial skeleton of a second adult were also discovered in the Lesedi chamber, which yielded 131 hominin remains.
The Rising Star cave system represents an extraordinary cache of hominin fossils – 1 500 individual fossil remains – representing 15 individuals. The remains included fossils ranging from foetal to adult stages of development, with potentially thousands of other individual remains still to be discovered in the chamber, says Berger.
Berger emphasises that the discovery was the result of work by a large team of scientists – 150 from across the world – while three studies published last week were the work of 53 scientists across three teams.
James Cook University and Wits geologist Professor Paul Dirks and his team used six different methods, confirmed independently by laboratories around the world, to accurately determine the age of the fossils and sediments.
Several techniques were used, including electron spin resonance (ESR), optically stimulated luminescence (OSL), palaeo- and geochronology methods, which involved determining the age of rocks, sediments and flowstones above and below and associated with the fossils using a range of geological and radiological methods and uranium-thorium dating methods to date fossil deposition.
Three teeth discovered in the Dinaledi chamber that had not been subjected to any scientific testing, which could affect the accuracy of the radiation dating ESR method used, were used to determine the precise age of the fossils.
“The range of methods and the rigour we applied to determine the age of the Dinaledi chamber and associated fossils give us great confidence that the age attributed to the fossils is correct and is between 236 000 years and 335 000 years before the present,” he says.
Berger highlights that the team of scientists was confident of making further discoveries and praised the explorers, research scientists analysing the fossil remains and the scientists who worked underground, including Dr Marina Elliott, one of the “underground astronauts” who excavated the fossils in Dinaledi – the chamber of the Stars – and in the Lesedi chamber.
The Homo naledi fossils from the Lesedi and Dinaledi chambers will be on display in the Cradle of Humankind Maropeng centre from May 25.