Heather M. Garvin

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa. DOI: http://dx.doi.org/10.7554/eLife.09560.001

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.

New fossil remains of Homo naledi from the Lesedi Chamber, South Africa

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species. DOI: http://dx.doi.org/10.7554/eLife.24232.001

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.

Body size, brain size, and sexual dimorphism in Homo naledi from the Dinaledi Chamber

Homo erectus and later humans have enlarged body sizes, reduced sexual dimorphism, elongated lower limbs, and increased encephalization compared to Australopithecus, together suggesting a distinct ecological pattern. The mosaic expression of such features in early Homo, including Homo habilis, Homo rudolfensis, and some early H.xa0erectus, suggests that these traits do not constitute an integrated package. We examined the evidence for body mass, stature, limb proportions, body size and dental size dimorphism, and absolute and relative brain size in Homo naledi as represented in the Dinaledi Chamber sample. H.xa0naledi stature and body mass are low compared to reported values for H.xa0erectus, with the exception of some of the smaller bodied Dmanisi H.xa0erectus specimens, and overlap with larger Australopithecus and early Homo estimates. H. naledi endocranial volumes (465-560xa0cc) and estimates of encephalization quotient are also similar to Australopithecus and low compared to all Homo specimens, with the exception of Homo floresiensis (LB1) and the smallest Dmanisi H.xa0erectus specimen (D4500). Unlike Australopithecus, but similar to derived members of genus Homo, the Dinaledi assemblage of H.xa0naledi exhibits both low levels of body mass and dental size variation, with an estimated body mass index of sexual dimorphism less than 20%, and appears to have an elongated lower limb. Thus, the H.xa0naledi bauplan combines features not typically seen in Homo species (e.g., small brains and bodies) with those characteristic of H.xa0erectus and more recent Homo species (e.g., reduced mass dimorphism, elongated lower limb).

Endocast morphology of Homo naledi from the Dinaledi Chamber, South Africa

Significance The new species Homo naledi was discovered in 2013 in a remote cave chamber of the Rising Star cave system, South Africa. This species survived until between 226,000 and 335,000 y ago, placing it in continental Africa at the same time as the early ancestors of modern humans were arising. Yet, H. naledi was strikingly primitive in many aspects of its anatomy, including the small size of its brain. Here, we have provided a description of endocast anatomy of this primitive species. Despite its small brain size, H. naledi shared some aspects of human brain organization, suggesting that innovations in brain structure were ancestral within the genus Homo. Hominin cranial remains from the Dinaledi Chamber, South Africa, represent multiple individuals of the species Homo naledi. This species exhibits a small endocranial volume comparable to Australopithecus, combined with several aspects of external cranial anatomy similar to larger-brained species of Homo such as Homo habilis and Homo erectus. Here, we describe the endocast anatomy of this recently discovered species. Despite the small size of the H. naledi endocasts, they share several aspects of structure in common with other species of Homo, not found in other hominins or great apes, notably in the organization of the inferior frontal and lateral orbital gyri. The presence of such structural innovations in a small-brained hominin may have relevance to behavioral evolution within the genus Homo.