The first hominin from the early Pleistocene paleocave of Haasgat, South Africa

Abstract

Haasgat is a primate-rich fossil locality in the northeastern part of the Fossil Hominid Sites of South Africa UNESCO World Heritage Site. Here we report the first hominin identified from Haasgat, a partial maxillary molar (HGT 500), that was recovered from an ex situ calcified sediment block sampled from the locality. The in situ fossil bearing deposits of the Haasgat paleokarstic deposits are estimated to date to slightly older than 1.95 Ma based on magnetobiostratigraphy. This places the hominin specimen at a critical time period in South Africa that marks the last occurrence of Australopithecus around 1.98 Ma and the first evidence of Paranthropus and Homo in the region between ∼2.0 and 1.8 Ma. A comprehensive morphological evaluation of the Haasgat hominin molar was conducted against the current South African catalogue of hominin dental remains and imaging analyses using micro-CT, electron and confocal microscopy. The preserved occlusal morphology is most similar to Australopithecus africanus or early Homo specimens but different from Paranthropus. Occlusal linear enamel thickness measured from micro-CT scans provides an average of ∼2.0 mm consistent with Australopithecus and early Homo. Analysis of the enamel microstructure suggests an estimated periodicity of 7–9 days. Hunter–Schreger bands appear long and straight as in some Paranthropus, but contrast with this genus in the short shape of the striae of Retzius. Taken together, these data suggests that the maxillary fragment recovered from Haasgat best fits within the Australopithecus—early Homo hypodigms to the exclusion of the genus Paranthropus. At ∼1.95 Ma this specimen would either represent another example of late occurring Australopithecus or one of the earliest examples of Homo in the region. While the identification of this first hominin specimen from Haasgat is not unexpected given the composition of other South African penecontemporaneous site deposits, it represents one of the few hominin localities in the topographically-distinct northern World Heritage Site. When coupled with the substantial differences in the mammalian faunal communities between the northern localities (e.g., Haasgat, Gondolin) and well-sampled Bloubank Valley sites (e.g., Sterkfontein, Swartkrans, Kromdraai), the recovery of the HGT 500 specimen highlights the potential for further research at the Haasgat locality for understanding the distribution and interactions of hominin populations across the landscape, ecosystems and fossil mammalian communities of early Pleistocene South Africa. Such contextual data from sites like Haasgat is critical for understanding the transition in hominin representation at ∼2 Ma sites in the region from Australopithecus to Paranthropus and early Homo.

Contemporaneity of Australopithecus , Paranthropus , and early Homo erectus in South Africa

“…However, the fragmented nature of most South African early Homo specimens (such as StW 53, SK 15, and SK 847) makes the taxonomy of this group and its relationship to eastern African Homo uncertain, with many fossil specimens assigned to multiple species or genera (4). An alternative hypothesis is that A. sediba could be the ancestor of South African Homo (8), despite being known from only ~2 million years (Ma) ago (9,10).…”

Optimizing the analysis of dental enamel microstructure in intact teeth

“…Cracks seem to be particularly frequent in fossil teeth (see figs. in Hlusko et al, ; Lacruz, Ramirez Rozzi, Wood, & Bromage, ; Leece et al, ; Xing et al, ). They will interfere with the path of laterally incident light used for HSBs visualization, causing a decrease in the degree of illumination when light crosses enamel cracks, with consequent loss of image quality.…”

“…Differences in the structure of HSBs among the various groups of mammals may be used to infer phylogenetic relationships, in the identification of mammalian taxa of higher orders (Ferretti, ; Line and Bergqvist, ; Koenigswald, ; Maas & Thewissen, ; Stefen, ), and personal identification (Ramenzoni & Line, ) and to infer diet adaptation (Tseng, ). The analysis of HSBs is usually performed by the use of polarizing light microscopy or scanning electron microscopy of sectioned or fractured teeth (Hanaizumi, Yokota, Domon, Wakita, & Kozawa, ; Lynch, O'sullivan, Dockery, McGillycuddy, & Sloan, ; Leece et al, ), where the observation is limited to the exposed area. Invasive or destructive procedures are not always suitable, especially in cases of rare specimens or specimens belonging to museum collections (Koenigswald, Holbrook, & Rose, ).…”

Digital enhancement of dental enamel microstructure images from intact teeth

“…Dental enamel is one of the most abundant and best-preserved tissues in fossil specimens. (Alba, Fortuny, & Moya-Sola, 2010;Hlusko et al, 2013;Leece et al, 2016;Xing et al;. Line and Bergqvist (2005) analyzed the structure of HSBs in enamel of intact mammalian teeth dating of approximately 60 million years.…”

“…The analysis of HSBs has been hindered by technical difficulties. In most cases the analysis HSBs is performed by the use of scanning electron microscopy or polarizing light microscopy in fractured or sectioned teeth (Hanaizumi, Yokota, Domon, Wakita, & Kozawa, ; Leece et al, ; Lynch, O'Sullivan, Dockery, McGillycuddy, & Sloan, ). Invasive or destructive procedures can cause irreversible damage and may not be performed in specimens belonging to private collections, especially if specimens are valuable or unique (Koenigswald et al, ).…”