Descriptive catalog of Homo naledi dental remains from the 2013 to 2015 excavations of the Dinaledi Chamber, site U.W. 101, within the Rising Star cave system, South Africa.

More than 150 hominin teeth, dated to ∼330-241 thousand years ago, were recovered during the 2013-2015 excavations of the Dinaledi Chamber of the Rising Star cave system, South Africa. These fossils comprise the first large single-site sample of hominin teeth from the Middle Pleistocene of Africa. Though scattered remains attributable to Homo sapiens, or their possible lineal ancestors, are known from older and younger sites across the continent, the distinctive morphological feature set of the Dinaledi teeth supports the recognition of a novel hominin species, Homo naledi. This material provides evidence of African Homo lineage diversity that lasts until at least the Middle Pleistocene. Here, a catalog, anatomical descriptions, and details of preservation and taphonomic alteration are provided for the Dinaledi teeth. Where possible, provisional associations among teeth are also proposed. To facilitate future research, we also provide access to a catalog of surface files of the Rising Star jaws and teeth.

Homo naledi cranial remains from the Lesedi chamber of the rising star cave system, South Africa.

Excavations in the Lesedi Chamber (U.W. 102) of the Rising Star cave system from 2013 to 2015 resulted in the recovery of 131 fossils representing at least three individuals attributed to Homo naledi. Hominin fossils were recovered from three collection areas within the Lesedi Chamber. A partial skull with near complete dentition (LES1) and an associated partial skeleton were recovered from Area 102a, while craniodental remains from two other individuals were recovered from Areas 102b and 102c. Here we present detailed anatomical descriptions and metrical comparisons of the Lesedi Chamber H. naledi craniodental remains that preserve diagnostic morphology. The LES1 skull is a presumed male that is slightly larger in size, and shows greater development of ectocranial structures compared to other H. naledi specimens from the Dinaledi Chamber of the Rising Star cave system. Otherwise the Lesedi fossils are notably similar to the Dinaledi fossils in shape and morphology. The Lesedi fossils also preserve the delicate nasal and lacrimal bones that are otherwise unrecorded in the Dinaledi sample. Limited morphological differences between the Dinaledi and Lesedi Chamber hominin samples provides support for the hypothesis that these two assemblages share a close phyletic relationship.

Description and analysis of three Homo naledi incudes from the Dinaledi Chamber, Rising Star cave (South Africa).

This study describes three incudes recovered from the Dinaledi Chamber in the Rising Star cave system in South Africa. All three bones were recovered during sieving of excavated sediments and likely represent three Homo naledi individuals. Morphologically and metrically, the Dinaledi ossicles resemble those of chimpanzees and Paranthropus robustus more than they do later members of the genus Homo, and fall outside of the modern human range of variation in several dimensions. Despite this, when overall size is considered, the functional lengths in H. naledi and P. robustus are very similar to those predicted for a human with a similar-sized incus. In this sense, both taxa seem to show a relatively elongated functional length, distinguishing them from chimpanzees. The functional length in H. naledi is slightly longer in absolute terms than in P. robustus, suggesting H. naledi may already show a slight increase in functional length compared with early hominins. While H. naledi lacks the more open angle between the long and short processes found in modern humans, considered a derived feature within the genus Homo, the value in H. naledi is similar to that predicted for a hominoid with a similar-sized incus. Principal components analysis of size-standardized variables shows H. naledi falling outside of the recent human range of variation, but within the confidence ellipse for gorillas. Phylogenetic polarity is complicated by the absence of incus data from early members of the genus Homo, but the generally primitive nature of the H. naledi incudes is consistent with other primitive features of the species, such as the very small cranial capacity. These ossicles add significantly to the understanding of incus variation in hominins and provide important new data on the morphology and taxonomic affinities of H. naledi.

The Biomechanics of Bony Facial "Buttresses" in South African Australopiths: An Experimental Study Using Finite Element Analysis.

Australopiths exhibit a number of derived facial features that are thought to strengthen the face against high and/or repetitive loads associated with a diet that included mechanically challenging foods. Here, we use finite element analysis (FEA) to test hypotheses related to the purported strengthening role of the zygomatic root and "anterior pillar" in australopiths. We modified our previously constructed models of Sts 5 (Australopithecus africanus) and MH1 (A. sediba) to differ in the morphology of the zygomatic root, including changes to both the shape and positioning of the zygomatic root complex, in addition to creating variants of Sts 5 lacking anterior pillars. We found that both an expanded zygomatic root and the presence of "anterior pillars" reinforce the face against feeding loads. We also found that strain orientations are most compatible with the hypothesis that the pillar evolved to resist loads associated with premolar loading, and that this morphology has an ancillary effect of strengthening the face during all loading regimes. These results provide support for the functional hypotheses. However, we found that an anteriorly positioned zygomatic root increases strain magnitudes even in models with an inflated/reinforced root complex. These results suggest that an anteriorly placed zygomatic root complex evolved to enhance the efficiency of bite force production while facial reinforcement features, such as the anterior pillar and the expanded zygomatic root, may have been selected for in part to compensate for the weakening effect of this facial configuration. Anat Rec, 300:171-195, 2017. © 2016 Wiley Periodicals, Inc.

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. naledi cranial and mandibular remains to investigate its morphological relationship with species of Homo and Australopithecus. We use Generalized Procrustes analysis to place H. naledi within the pattern of known hominin skull diversity, distributions of Procrustes distances among individuals to compare H. naledi 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. naledi, its affinity with H. erectus, and the age of the fossils based on skull morphology. Our results indicate that, cranially, H. naledi aligns with members of the genus Homo, with closest affiliations to H. erectus. The mandibular results are less clear; H. naledi closely associates with a number of taxa, including some australopiths. However, results also show that although H. naledi shares similarities with H. erectus, some distances from this taxon - especially small-brained members of this taxon - are extreme. The neighbor joining trees place H. naledi firmly within Homo. The trees based on cranial morphology again indicate a close relationship between H. naledi and H. erectus, whereas the mandibular tree places H. naledi closer to basal Homo, suggesting a deeper antiquity. Altogether, these results emphasize the unique combination of features (H. erectus-like cranium, less derived mandible) defining H. naledi. 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. naledi 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. naledi 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.

Comparative biomechanics of Australopithecus sediba mandibles.

Fossils attributed to Australopithecus sediba are described as having phylogenetic affinities with early Homo to the exclusion of other South African australopiths. With respect to functional anatomy of mastication, one implication of this hypothesis is that A. sediba mandibles should exhibit absolutely and relatively reduced stiffness and strength in comparison to Australopithecus africanus and Paranthropus robustus jaws. Examination of cortical bone distribution in the MH 1 and MH 2 mandibles of A. sediba (evaluated against samples of Pan, early and modern Homo as well as A. africanus and P. robustus) indicate that the A. sediba mandibular corpus was geometrically similar to other South African australopiths. In particular, enhanced torsional rigidity is characteristic of all South African australopiths including A. sediba. These findings are consistent with a hypothesis that masticatory mechanics may have been similar to other australopiths (and distinct from exemplars of early Homo), and as such suggest that A. sediba's mandibles were functionally suited to consume hard and tough objects. Recent mechanical modeling of the A. sediba cranium, however, has been interpreted as indicating that this species was relatively poorly adapted to produce large bite forces and likely experienced relatively modest strains in its facial skeleton. This paradox - that the cranium signals a departure from the australopith morphotype whereas the mandibles conform to a hypodigm of australopith grade - can be resolved, in part, if it is acknowledged that mechanical performance variables offer imperfect insight into what constitutes feeding adaptations.

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. naledi but some important questions remain unanswered. Here we report a study that addressed two of them: "Where does H. naledi 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. naledi. Then we employed Bayes factor tests to compare the strength of support for hypotheses about the relationships of H. naledi suggested by the best-estimate trees. Lastly, we carried out a resampling analysis to assess the accuracy of the age estimate for H. naledi yielded by the dated Bayesian analysis. The analyses strongly supported the hypothesis that H. naledi forms a clade with the other Homo species and Australopithecus sediba. The analyses were more ambiguous regarding the position of H. naledi 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. naledi. According to the dated Bayesian analysis, the most likely age for H. naledi is 912 ka. 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. naledi is simply a variant of H. erectus, and suggest H. naledi is younger than has been previously proposed.

The apportionment of tooth size and its implications in Australopithecus sediba versus other Plio-pleistocene and recent African hominins.

OBJECTIVES: Australopithecus sediba is characterized further by providing formerly unpublished and refined mesiodistal and buccolingual crown measurements in the MH1 and MH2 specimens. After size correction, these data were compared with those in other fossil and recent samples to facilitate additional insight into diachronic hominin affinities. MATERIALS AND METHODS: Six comparative samples consist of fossil species: A. africanus, A. afarensis, Homo habilis, Paranthropus robustus, P. boisei, and H. erectus. Others comprise H. sapiens and Pan troglodytes. Re-estimates of "actual" dimensions in damaged A. sediba teeth were effected through repeated measurements by independent observers. X-ray synchrotron microtomography allowed measurement of crowns obscured by matrix and noneruption. Tooth size apportionment analysis, an established technique for intraspecific comparisons, was then applied at this interspecific level to assess phenetic affinities using both within- and among-group data. RESULTS: Comparison of these highly heritable dimensions identified a general trend for smaller posterior relative to larger anterior teeth (not including canines), contra Paranthropus, that allies A. sediba with other australopiths and Homo; however, specific reductions and/or shape variation in the species' canines, third premolars, and anterior molars relative to the other teeth mirror the patterning characteristic of Homo. DISCUSSSION: Of all samples, including east African australopiths, A. sediba appears most like H. habilis, H. erectus and H. sapiens regarding how crown size is apportioned along the tooth rows. These findings parallel those in prior studies of dental and other skeletal data, including several that suggest A. sediba is a close relative of, if not ancestral to, Homo.

Mechanical evidence that Australopithecus sediba was limited in its ability to eat hard foods.

Australopithecus sediba has been hypothesized to be a close relative of the genus Homo. Here we show that MH1, the type specimen of A. sediba, was not optimized to produce high molar bite force and appears to have been limited in its ability to consume foods that were mechanically challenging to eat. Dental microwear data have previously been interpreted as indicating that A. sediba consumed hard foods, so our findings illustrate that mechanical data are essential if one aims to reconstruct a relatively complete picture of feeding adaptations in extinct hominins. An implication of our study is that the key to understanding the origin of Homo lies in understanding how environmental changes disrupted gracile australopith niches. Resulting selection pressures led to changes in diet and dietary adaption that set the stage for the emergence of our genus.

Early hominin auditory capacities.

Studies of sensory capacities in past life forms have offered new insights into their adaptations and lifeways. Audition is particularly amenable to study in fossils because it is strongly related to physical properties that can be approached through their skeletal structures. We have studied the anatomy of the outer and middle ear in the early hominin taxa Australopithecus africanus and Paranthropus robustus and estimated their auditory capacities. Compared with chimpanzees, the early hominin taxa are derived toward modern humans in their slightly shorter and wider external auditory canal, smaller tympanic membrane, and lower malleus/incus lever ratio, but they remain primitive in the small size of their stapes footplate. Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies. The results have implications for sensory ecology and communication, and suggest that the early hominin auditory pattern may have facilitated an increased emphasis on short-range vocal communication in open habitats.

Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa.

We describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. The chamber was always in the dark zone, and not accessible to non-hominins. Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occurring during/after deposition. Hominins accumulated over time as older laminated mudstone units and sediment along the cave floor were eroded. Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date.

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.

PALEOANTHROPOLOGY. Comment on "Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia".

Villmoare et al. (Reports, 20 March 2015, p. 1352) report on a hominin mandible from the Ledi-Geraru research area, Ethiopia, which they claim to be the earliest known representative of the genus Homo. However, certain measurements and observations for Australopithecus sediba mandibles presented are incorrect or are not included in critical aspects of the study. When correctly used, these data demonstrate that specimen LD 350-1 cannot be unequivocally assigned to the genus Homo.

Early hominin auditory ossicles from South Africa.

The middle ear ossicles are only rarely preserved in fossil hominins. Here, we report the discovery of a complete ossicular chain (malleus, incus, and stapes) of Paranthropus robustus as well as additional ear ossicles from Australopithecus africanus. The malleus in both early hominin taxa is clearly human-like in the proportions of the manubrium and corpus, whereas the incus and stapes resemble African and Asian great apes more closely. A deep phylogenetic origin is proposed for the derived malleus morphology, and this may represent one of the earliest human-like features to appear in the fossil record. The anatomical differences found in the early hominin incus and stapes, along with other aspects of the outer, middle, and inner ear, are consistent with the suggestion of different auditory capacities in these early hominin taxa compared with modern humans.

Mandibular remains support taxonomic validity of Australopithecus sediba.

Since the announcement of the species Australopithecus sediba, questions have been raised over whether the Malapa fossils represent a valid taxon or whether inadequate allowance was made for intraspecific variation, in particular with reference to the temporally and geographically proximate species Au. africanus. The morphology of mandibular remains of Au. sediba, including newly recovered material discussed here, shows that it is not merely a late-surviving morph of Au. africanus. Rather-as is seen elsewhere in the cranium, dentition, and postcranial skeleton-these mandibular remains share similarities with other australopiths but can be differentiated from the hypodigm of Au. africanus in both size and shape as well as in their ontogenetic growth trajectory.

Dental morphology and the phylogenetic "place" of Australopithecus sediba.

To characterize further the Australopithecus sediba hypodigm, we describe 22 dental traits in specimens MH1 and MH2. Like other skeletal elements, the teeth present a mosaic of primitive and derived features. The new nonmetric data are then qualitatively and phenetically compared with those in eight other African hominin samples, before cladistic analyses using a gorilla outgroup. There is some distinction, largely driven by contrasting molar traits, from East African australopiths. However, Au. sediba links with Au. africanus to form a South African australopith clade. These species present five apomorphies, including shared expressions of Carabelli's upper first molar (UM1) and protostylid lower first molar (LM1). Five synapomorphies are also evident between them and monophyletic Homo habilis/rudolfensis + H. erectus. Finally, a South African australopith + Homo clade is supported by four shared derived states, including identical LM1 cusp 7 expression.

The upper limb of Australopithecus sediba.

The evolution of the human upper limb involved a change in function from its use for both locomotion and prehension (as in apes) to a predominantly prehensile and manipulative role. Well-preserved forelimb remains of 1.98-million-year-old Australopithecus sediba from Malapa, South Africa, contribute to our understanding of this evolutionary transition. Whereas other aspects of their postcranial anatomy evince mosaic combinations of primitive (australopith-like) and derived (Homo-like) features, the upper limbs (excluding the hand and wrist) of the Malapa hominins are predominantly primitive and suggest the retention of substantial climbing and suspensory ability. The use of the forelimb primarily for prehension and manipulation appears to arise later, likely with the emergence of Homo erectus.

Mosaic morphology in the thorax of Australopithecus sediba.

The shape of the thorax of early hominins has been a point of contention for more than 30 years. Owing to the generally fragmentary nature of fossil hominin ribs, few specimens have been recovered that have rib remains complete enough to allow accurate reassembly of thoracic shape, thus leaving open the question of when the cylindrical-shaped chest of humans and their immediate ancestors evolved. The ribs of Australopithecus sediba exhibit a mediolaterally narrow, ape-like upper thoracic shape, which is unlike the broad upper thorax of Homo that has been related to the locomotor pattern of endurance walking and running. The lower thorax, however, appears less laterally flared than that of apes and more closely approximates the morphology found in humans.