Fossil hominins from South Africa are enriching the story of early human evolution and dispersal. Herries et al. describe the geological context and dating of the hominin-bearing infilled cave, or palaeocave, at a site called Drimolen in South Africa (see the Perspective by Antón). They focus on the age and context of a recently discovered Homo erectus sensu lato fossil and a Paranthropus robustus fossil, which they dated to ∼2.04 million to 1.95 million years ago. This makes Drimolen one of the best-dated sites in South Africa and establishes these fossils as the oldest definitive specimens of their respective species ever discovered. The age confirms that species of Australopithecus, Paranthropus, and early Homo overlapped in the karst of South Africa ∼2 million years ago.

Structured Abstract

INTRODUCTION Drimolen is one of several ancient caves located in the Hominid Caves of South Africa United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Area in South Africa. Between ~2.3 million and ~1.8 million years ago, there were major climactic changes and faunal turnovers in the region, including the last occurrence of the genus Australopithecus and the first occurrence of Paranthropus and Homo, as well as the first occurrence of stone and bone tools. However, the exact nature of these changes has been hard to elucidate because of past difficulties in dating caves of this age and their perceived geological complexity. Unlike in eastern Africa, where volcanic material is available for dating, the South African caves have been dated with a variety of evolving methods that have often given conflicting age estimates. This means that South Africa’s early human record and its relationship to east African hominin species have been difficult to determine. This is especially problematic given that each record is distinct in terms of hominin species until perhaps the origin and early evolution of the genus Homo. Although many fragmentary fossil specimens in South Africa have been attributed to early Homo, there is no consensus regarding species attribution.

RATIONALE Drimolen Main Quarry has yielded one of the richest records of early human fossils in South Africa, including examples of Homo and the most complete female skull (DNH 7) of Paranthropus robustus. Excavations between 2015 and 2018 yielded the first new hominin calvaria (DNH 134 and DNH 152) from the site in 20 years. A combination of uranium-lead dating on flowstones, uranium-series electron spin resonance (US-ESR) dating on teeth, and palaeomagnetism on sediments was undertaken to establish the age of the site and its early human fossils.

RESULTS The DNH 134 cranium shares clear affinities with Homo erectus, whereas the DNH 152 cranium represents P. robustus. Stratigraphic analysis of the Drimolen Main Quarry deposits indicates that unlike many other South African sites, there was only one major phase of relatively short deposition between ~2.04 million years ago and ~1.95 million years ago. This age has been constrained by the identification of the ~1.95-million-year-old magnetic field reversal at the base of the Olduvai SubChron within the sediments and by the direct uranium-lead dating of a flowstone that formed during the reversal. This has been augmented by direct dating on fossils by means of US-ESR that suggests that the DNH 134 and DNH 152 crania were deposited just before this reversal, with the DNH 134 crania deposited at ~2.04 million years ago. The DNH 134 cranium shares affinities with H. erectus and predates all known specimens in that species. The age range of Drimolen Main Quarry overlaps with that of Australopithecus sediba from the nearby site of Malapa and indicates that Homo, Paranthropus, and Australopithecus were contemporaneous in South Africa between 2.04 million and 1.95 million years ago. It is the first time that dating has conclusively demonstrated that these three taxa shared the same landscape during the same time range, making it less likely that a population of A. sediba is ancestral to Homo, as has been previously suggested. Analysis of fauna preserved at Drimolen documents a period of ecological change, with earlier South African species going extinct and new species moving into the region from other parts of Africa, including early representatives of H. erectus.