Presenter: Dr Ashley Kruger Naturhistoriska riksmuseet, Stockholm, Sweden. Photo: John Hawks.

Summary

The role of digital data in the discovery of Homo naledi: a new human ancestor from the Cradle of Humankind, South Africa

A recently discovered site in the Rising Star Cave, Cradle of Humankind, Johannesburg, South Africa, has yielded the single largest fossil hominin assemblage on the African continent to have been uncovered to date. Much of the anatomy of the new species, Homo naledi, has been described. With a relatively derived lower limb and strangely primitive-like upper body, Homo naledi displays a mosaic of traits in its morphology. The assemblage is remarkably homogenous, and almost completely monospecific.

Homo Naledi. Photo: John Gurche.

The chamber in which Homo naledi was discovered, the Dinaledi Chamber, is accessible only through a nearvertical chute that presented immense practical and methodological limitations on the excavation and recording methods that could be used within the cave. The chamber preserves bone material within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. This non-brecciated deposit is distinctive from almost all other fossil hominin sites in the Cradle of Humankind. The chamber has always been in the dark zone, and taphonomic analysis of the almost 1550 specimens recovered has shown that the Dinaledi Chamber was not accessible to non-hominins.

In order to further understand the context of the Dinaledi assemblage, and to map and analyse the excavations, a high-resolution three-dimensional (3D) multimodal set of recording strategies was developed and employed for use at the site. Recording of fossils and the excavation process were achieved through the use of whitelight photogrammetry, and mapping of the Dinaledi Chamber was accomplished by means of high-resolution laser scanning, with scans running from the excavation site to both the ground surface and the cave entrance. The integration of conventional surveying techniques as well as photogrammetry with the use of an unmanned aerial vehicle (drone) provided further spatial constraints to the landscape above the cave system.

The Lasedi chamber. Photo: Elliott Ross.

In the laboratory, additional scanning techniques have allowed for the reconstruction of fossil elements. These techniques included 3D surface laser scanning and X-ray computed tomography (CT). CT data in particular, were used to provide digital reconstructions of the Homo naledi internal cranial vault (endocast), and to peer inside fossil masses recovered from the cave system which have yet to be excavated from their plaster jackets.

The site is unique as it presents no evidence for peri-mortem breakage or trauma indicative of a fall or death trap, no carnivore modifications, no cut marks, no sub-aerial exposure or weathering indicative of death outside the cave, no evidence of water transportation of bodies or bones within the cave, and no evidence of burning or charring. This has lead researchers to offer the ‘deliberate disposal hypothesis’, a hypothesis suggesting that the small-brained Homo naledi purposefully journeyed to the chamber to deliberately dispose of their dead; a behaviour previously thought to be unique to humans.

Now, a second Homo naledi assemblage has been discovered in another part of the same cave, and is named the Lesedi Chamber. This chamber begs even more questions about the already fascinating story of this species which has been dated to between 236,000 and 335,000 years ago. These dates suggest that Homo naledi may have once shared the landscape with our own species, Homo sapiens, in southern Africa.