Biochronology of South African hominin-bearing sites: A reassessment using cercopithecid primates

The large mammal fossil fauna of the Cradle of Humankind, South Africa: a review

South Africa's Cradle of Humankind UNESCO World Heritage Site has remained the single richest source of hominin fossils for over ninety years. While its hominin specimens have been the subject of extensive research, the same is not true for its abundant faunal assemblages, despite their value in Plio-Pleistocene palaeoenvironmental reconstructions. Moreover, precise ages and depositional histories have been historically difficult to assess, though advancements in both relative and absolute dating techniques are changing this. This review explores the history of non-hominin large mammal faunal reporting, palaeoenvironmental reconstructions based on these fauna, and dating histories (with a focus on biochronology) at the following eight fossil-bearing sites of the Cradle that have been radiometrically dated with uranium-lead: Bolt's Farm, Cooper's Cave, Drimolen, Haasgat, Hoogland, Malapa, Sterkfontein and Swartkrans. Continued efforts to provide more precise and direct ages for sites using a variety of methods indicate that the bulk of Cradle deposits date to between 3 and 1.4 Ma. We find that, across almost all eight sites, there is little discussion or debate surrounding faunal reports, with some sites described by a single publication. Many of the reports are decades old with little review or reanalysis in the years following, emphasising the need for reviews such as this one. Our analysis of the data indicates that faunal-based paleoenvironmental reconstructions across sites commonly show a trend of wooded landscapes giving way to grasslands. We find that these reconstructions are primarily based on faunal abundance data, despite the availability of many other informative analytical techniques. The findings of this review highlight a need for more extensive and robust faunal reporting, as this will aid in understanding the context of these Cradle sites.

Australopithecus at Sterkfontein did not consume substantial mammalian meat

Incorporation of animal-based foods into early hominin diets has been hypothesized to be a major catalyst of many important evolutionary events, including brain expansion. However, direct evidence of the onset and evolution of animal resource consumption in hominins remains elusive. The nitrogen-15 to nitrogen-14 ratio of collagen provides trophic information about individuals in modern and geologically recent ecosystems (<200,000 years ago), but diagenetic loss of this organic matter precludes studies of greater age. By contrast, nitrogen in tooth enamel is preserved for millions of years. We report enamel-bound organic nitrogen and carbonate carbon isotope measurements of Sterkfontein Member 4 mammalian fauna, including seven Australopithecus specimens. Our results suggest a variable but plant-based diet (largely C3) for these hominins. Therefore, we argue that Australopithecus at Sterkfontein did not engage in regular mammalian meat consumption.

A biochronological date of 3.6 million years for "Little Foot" (StW 573, Australopithecus prometheus from Sterkfontein, South Africa)

A debate has developed with regard to geological ages of hominin fossils attributed to Australopithecus africanus and Australopithecus prometheus in South African Plio-Pleistocene cave deposits. For the Sterkfontein caves (Members 2 and 4), cosmogenic nuclide isochron (10Be/26Al) dating has yielded age estimates ranging from 3.4 to 3.7 million years ago (Ma). However, biochronological approaches using nonhominin primates suggest an alternative age range between 2 and 2.6 Ma. Based on a new method of hominin biochronology, Thackeray and Dykes have recognized that Sterkfontein Member 4 has a mean age of 2.76 Ma associated with a wide range (circa 2.0-3.5 Ma). In this study, the Sterkfontein skull and skeleton (StW 573), nicknamed "Little Foot" from Member 2 and attributed to A. prometheus, is reassessed. A regression model applied to estimate its age provides a hypothesized date of 3.6 Ma, which compares favorably with the existing cosmogenic dates.

Dart and the Taung juvenile: making sense of a century-old record of hominin evolution in Africa

The announcement in 1925 by Raymond Dart of the discovery of the Taung juvenile's skull in a quarry in sub-Saharan Africa is deservedly a classic publication in the history of palaeoanthropology. Dart's paper-which designated Taung as the type specimen of the early hominin species Australopithecus africanus-provided the first fossil evidence supporting Charles Darwin's 1871 prediction that Africa was where the human lineage originated. The Taung juvenile's combination of ape and human characteristics eventually led to a paradigm shift in our understanding of human evolution. This contribution focuses on the milieu in which Dart's paper appeared (i.e. what was understood in 1925 about human evolution), the fossil evidence as set out by Dart, his interpretation of how a species represented by a fossilized juvenile's skull fitted within prevailing narratives about human evolution and the significance of the fossil being found in an environment inferred to be very different from that occupied by living apes. We also briefly review subsequent fossil finds that have corroborated the argument Dart made for having discovered evidence of a hitherto unknown close relative of humans, and summarize our current understanding of the earliest stages of human evolution and its environmental context.

Combined uranium-series and electron spin resonance dating from the Pliocene fossil sites of Aves and Milo's palaeocaves, Bolt's Farm, Cradle of Humankind, South Africa

Bolt's Farm is the name given to a series of non-hominin bearing fossil sites that have often been suggested to be some of the oldest Pliocene sites in the Cradle of Humankind, South Africa. This article reports the results of the first combined Uranium-Series and Electron Spin Resonance (US-ESR) dating of bovid teeth at Milo's Cave and Aves Cave at Bolt's Farm. Both tooth enamel fragments and tooth enamel powder ages were presented for comparison. US-ESR, EU and LU models are calculated. Overall, the powder ages are consistent with previous uranium-lead and palaeomagnetic age estimates for the Aves Cave deposit, which suggest an age between ~3.15 and 2.61 Ma and provide the first ages for Milo's Cave dates to between ~3.1 and 2.7 Ma. The final ages were not overly dependent on the models used (US-ESR, LU or EU), which all overlap within error. These ages are all consistent with the biochronological age estimate (<3.4->2.6 Ma) based on the occurrence of Stage I Metridiochoerus andrewsi. Preliminary palaeomagnetic analysis from Milo's Cave indicates a reversal takes place at the site with predominantly intermediate directions, suggesting the deposit may date to the period between ~3.03 and 3.11 Ma within error of the ESR ages. This further suggests that there are no definitive examples of palaeocave deposits at Bolt's Farm older than 3.2 Ma. This research indicates that US-ESR dating has the potential to date fossil sites in the Cradle of Humankind to over 3 Ma. However, bulk sample analysis for US-ESR dating is recommended for sites over 3 Ma.

Description and taxonomic assessment of fossil Cercopithecidae from the Pliocene Galili Formation (Ethiopia)

The Mount Galili Formation in the Afar region, Ethiopia, samples a critical time in hominin evolution, 4.4 to 3.8 Ma, documenting the last appearance of Ardipithecus and the origin of Australopithecus. This period is also important in the evolution of cercopithecids, especially the origin of Theropithecus in general and Theropithecus oswaldi lineage in particular. Galili has provided a total of 655 cercopithecid specimens that include crania, mandibles, isolated teeth and postcrania. All the fossils were recovered from the Lasdanan (5.3-4.43 Ma), Dhidinley (4.43-3.9 Ma) and Shabeley Laag (∼3.92-3.8 Ma) Members. Here, we described and analyzed 362 fossils employing both qualitative and quantitative methods. Descriptions of the material were supplemented with dental metrics and cranial shape analysis using three-dimensional geometric morphometrics. Results indicate the presence of at least six cercopithecid taxa: Theropithecus oswaldi serengetensis (n = 28), Theropithecus sp. (n = 2), three non-Theropithecus papionin groups (n = 134) and one colobine-size group (n = 58). The T. o. serengetensis represents the earliest form of the lineage, documented from ∼3.9 Ma Galili sediments. The three Galili papionins include a smaller taxon, a medium-sized taxon comparable to Pliopapio alemui and a large papionin overlapping in size with Soromandrillus, Gorgopithecus and Dinopithecus. The majority of Galili colobines have closest affinities to Kuseracolobus aramisi and some overlap with other taxa. Papionins dominate the Galili cercopithecid collection, although colobines are still fairly common (approximately 25% of the sample). Thus, Galili sample is like Kanapoi (4.2-4.1 Ma) and Gona (5.2-3.9 Ma) localities but distinct from Aramis, suggesting paleoecological similarity to the former sites. On the other hand, Theropithecus is less abundant at Galili than geologically younger Hadar (3.4-3.2 Ma) and Woranso-Mille (3.8-3.6 Ma) sites. Whether this difference is due to sampling, time or landscape variation requires further investigation.

A lineage perspective on hominin taxonomy and evolution

An uncritical reliance on the phylogenetic species concept has led paleoanthropologists to become increasingly typological in their delimitation of new species in the hominin fossil record. As a practical matter, this approach identifies species as diagnosably distinct groups of fossils that share a unique suite of morphological characters but, ontologically, a species is a metapopulation lineage segment that extends from initial divergence to eventual extinction or subsequent speciation. Working from first principles of species concept theory, it is clear that a reliance on morphological diagnosabilty will systematically overestimate species diversity in the fossil record; because morphology can evolve within a lineage segment, it follows that early and late populations of the same species can be diagnosably distinct from each other. We suggest that a combination of morphology and chronology provides a more robust test of the single-species null hypothesis than morphology alone.

Plio-Pleistocene African megaherbivore losses associated with community biomass restructuring

Fossil abundance data can reveal ecological dynamics underpinning taxonomic declines. Using fossil dental metrics, we reconstructed body mass and mass-abundance distributions in Late Miocene to recent African large mammal communities. Despite collection biases, fossil and extant mass-abundance distributions are highly similar, with unimodal distributions likely reflecting savanna environments. Above 45 kilograms, abundance decreases exponentially with mass, with slopes close to -0.75, as predicted by metabolic scaling. Furthermore, communities before ~4 million years ago had considerably more large-sized individuals, with a greater proportion of total biomass allocated in larger size categories, than did later communities. Over time, individuals and biomass were redistributed into smaller size categories, reflecting a gradual loss of large-sized individuals from the fossil record paralleling the long-term decline of Plio-Pleistocene large mammal diversity.

A review of Theropithecus oswaldi with the proposal of a new subspecies

Theropithecus oswaldi darti, as currently understood, is the oldest Theropithecus taxon in the fossil record and the earliest subspecies in the Theropithecusoswaldi lineage. Theropithecus oswaldi darti is typified at the site of Makapansgat in South Africa, and a similar form (T. o. cf. darti) is usually recognized at Hadar, Dikika, some Middle Awash localities, and Woranso-Mille in Ethiopia. This taxon is also tentatively believed to occur in Kenya at Kanam and Koobi Fora and in Member C of the Shungura Formation in Ethiopia. While there is a general consensus that the East African 'darti' specimens are sufficiently similar to each other, there has always been a question of whether they are too distinct from the South African type material of T. o. darti to belong to the same subspecies. Here we conduct a morphological comparison of the different samples previously assigned to T. o. darti and T. o. cf. darti. The results of our analyses overwhelmingly support the hypothesis that the East African samples are distinct from the South African ones, and they are likely distinct in geological age as well. Therefore, we propose a new subspecies designation for the material previously termed T. o. cf. darti from East Africa: Theropithecus (Theropithecus) oswaldi ecki subsp. nov. We also formally recognize Theropithecus (Theropithecus) oswaldi serengetensis (Dietrich, 1942) for specimens from Laetoli, Woranso-Mille, and perhaps Galili.