Darryl J. de Ruiter

Strontium isotope evidence for landscape use by early hominins

Ranging and residence patterns among early hominins have been indirectly inferred from morphology, stone-tool sourcing, referential models and phylogenetic models. However, the highly uncertain nature of such reconstructions limits our understanding of early hominin ecology, biology, social structure and evolution. We investigated landscape use in Australopithecus africanus and Paranthropus robustus from the Sterkfontein and Swartkrans cave sites in South Africa using strontium isotope analysis, a method that can help to identify the geological substrate on which an animal lived during tooth mineralization. Here we show that a higher proportion of small hominins than large hominins had non-local strontium isotope compositions. Given the relatively high levels of sexual dimorphism in early hominins, the smaller teeth are likely to represent female individuals, thus indicating that females were more likely than males to disperse from their natal groups. This is similar to the dispersal pattern found in chimpanzees, bonobos and many human groups, but dissimilar from that of most gorillas and other primates. The small proportion of demonstrably non-local large hominin individuals could indicate that male australopiths had relatively small home ranges, or that they preferred dolomitic landscapes.

The evolutionary relationships and age of Homo naledi: an assessment using dated Bayesian phylogenetic methods

Homo naledi is a recently discovered species of fossil hominin from South Africa. A considerable amount is already known about H.xa0naledi but some important questions remain unanswered. Here we report a study that addressed two of them: Where does H.xa0naledi fit in the hominin evolutionary tree? and How old is it? We used a large supermatrix of craniodental characters for both early and late hominin species and Bayesian phylogenetic techniques to carry out three analyses. First, we performed a dated Bayesian analysis to generate estimates of the evolutionary relationships of fossil hominins including H.xa0naledi. Then we employed Bayes factor tests to compare the strength of support for hypotheses about the relationships of H.xa0naledi suggested by the best-estimate trees. Lastly, we carried out a resampling analysis to assess the accuracy of the age estimate for H.xa0naledi yielded by the dated Bayesian analysis. The analyses strongly supported the hypothesis that H.xa0naledi forms a clade with the other Homo species and Australopithecus sediba. The analyses were more ambiguous regarding the position of H.xa0naledi within the (Homo, Au. sediba) clade. A number of hypotheses were rejected, but several others were not. Based on the available craniodental data, Homo antecessor, Asian Homo erectus, Homo habilis, Homo floresiensis, Homo sapiens, and Au. sediba could all be the sister taxon of H.xa0naledi. According to the dated Bayesian analysis, the most likely age for H.xa0naledi is 912xa0ka. This age estimate was supported by the resampling analysis. Our findings have a number of implications. Most notably, they support the assignment of the new specimens to Homo, cast doubt on the claim that H.xa0naledi is simply a variant of H.xa0erectus, and suggest H.xa0naledi is younger than has been previously proposed.

Skull diversity in the Homo lineage and the relative position of Homo naledi

The discovery of Homo naledi has expanded the range of phenotypic variation in Homo, leading to new questions surrounding the mosaic nature of morphological evolution. Though currently undated, its unique morphological pattern and possible phylogenetic relationships to other hominin taxa suggest a complex evolutionary scenario. Here, we perform geometric morphometric analyses on H.xa0naledi cranial and mandibular remains to investigate its morphological relationship with species of Homo and Australopithecus. We use Generalized Procrustes analysis to place H.xa0naledi within the pattern of known hominin skull diversity, distributions of Procrustes distances among individuals to compare H.xa0naledi and Homo erectus, and neighbor joining trees to investigate the potential phenetic relationships between groups. Our goal is to address a set of hypotheses relating to the uniqueness of H.xa0naledi, its affinity with H.xa0erectus, and the age of the fossils based on skull morphology. Our results indicate that, cranially, H.xa0naledi aligns with members of the genus Homo, with closest affiliations to H.xa0erectus. The mandibular results are less clear; H.xa0naledi closely associates with a number of taxa, including some australopiths. However, results also show that although H.xa0naledi shares similarities with H.xa0erectus, some distances from this taxon - especially small-brained members of this taxon - are extreme. The neighbor joining trees place H.xa0naledi firmly within Homo. The trees based on cranial morphology again indicate a close relationship between H.xa0naledi and H.xa0erectus, whereas the mandibular tree places H.xa0naledi closer to basal Homo, suggesting a deeper antiquity. Altogether, these results emphasize the unique combination of features (H.xa0erectus-like cranium, less derived mandible) defining H.xa0naledi. Our results also highlight the variability within Homo, calling for a greater focus on the cause of this variability, and emphasizing the importance of using the total morphological package for species diagnoses.

The skull of Homo naledi

The species Homo naledi was recently named from specimens recovered from the Dinaledi Chamber of the Rising Star cave system in South Africa. This large skeletal sample lacks associated faunal material and currently does not have a known chronological context. In this paper, we present comprehensive descriptions and metric comparisons of the recovered cranial and mandibular material. We describe 41 elements attributed to Dinaledi Hominin (DH1-DH5) individuals and paratype U.W. 101-377, and 32 additional cranial fragments. The H.xa0naledi material was compared to Plio-Pleistocene fossil hominins using qualitative and quantitative analyses including over 100 linear measurements and ratios. We find that the Dinaledi cranial sample represents an anatomically homogeneous population that expands the range of morphological variation attributable to the genus Homo. Despite a relatively small cranial capacity that is within the range of australopiths and a few specimens of early Homo, H. naledi shares cranial characters with species across the genus Homo, including Homo habilis, Homo rudolfensis, Homo erectus, and Middle Pleistocene Homo. These include aspects of cranial form, facial morphology, and mandibular anatomy. However, the skull of H.xa0naledi is readily distinguishable from existing species of Homo in both qualitative and quantitative assessments. Since H. naledi is currently undated, we discuss the evolutionary implications of its cranial morphology in a range of chronological frameworks. Finally, we designate a sixth Dinaledi Hominin (DH6) individual based on a juvenile mandible.