Health Sciences

Materials: Comparative data were collected on ribs 1-12 from samples of Homo sapiens (n=30), Pan troglodytes (n=16), Pongo pygmaeus/abelii (n=12) and Hylobates lar (N=20) from the A.H. Schultz Collection at the Anthropological Institute and Museum of the University of Zurich. Specimens were selected for completeness of the rib series and were primarily adult. To augment sample sizes, subadults (nearing maturity, and of a developmental age roughly comparable to that of Malapa Hominin 1) were included in the human (n = 1), chimpanzee (n = 7), and orangutan (n = 3) samples . Data were collected on the original specimens of Au. sediba MH1 and MH2.

The thoracic skeletal morphology of homininae is poorly known and understood. As a result of the representative fossil record of ribs and vertebrae being rare, distorted, fragmentary or unrecognised even when recovered, very little is known about the variability of rib and vertebral morphology when compared to the other cranial and postcranial elements in this lineage. Yet the costal skeleton forms a substantial part of the postcranial skeleton and thus ribs and vertebrae are therefore potentially numerous in the fossil record; but in comparison with other skeletal elements, and for the reasons mentioned above, very little is known about vertebrate and especially hominin rib morphology. The assessment of the structure of the thoracic skeletal elements and its evolutionary and ecological significance, particularly in the Homininae, poses a challenge but is still important as the shape and form of the rib cage has numerous functional and behavioural implications. The present study analysed the ribs of selected primate and non-primate mammalian species by examining fifteen variables, seven indices and eight osteological non-metric features.

Hybridization is widespread among sexually reproducing groups of organisms, and results in the transfer of genes from one lineage to another. For hominins, a number of recent genetic studies have revealed a complex picture of lineage divergence and reticulation, resulting in the diversity we see among humans today. These studies have primarily focussed on the contact between lineages in Eurasia in the late Pleistocene, although studies of African diversity and ancient DNA from earlier time periods have added to the picture of widespread gene exchange. Although ancient DNA in particular has begun to provide important insight into the dynamics of this gene exchange, sample size and preservation limit its applicability, especially for providing details on precisely where and when gene exchange occurred, and examining gene exchange in the deeper past. Moreover, as studies from other organisms (e.g. bears) indicate, there are multiple scenarios by which we can get to a final product of, say ca. 3% introgressed DNA; only a finer grained temporal record, correlated with a deeper understanding of behavioural and environmental change, can provide us with such information. Here we present ongoing research into the effects of hybridization on the phenotype of three mammals: mice, baboons, and macaques. This research provides alternative but also complementary means for identifying hybrids in the past, such as Oase 1 & 2, thereby potentially increasing the resolution of our record. Previous studies focussed on understanding and quantifying cranial variation in one of these primates (Papio baboons) as well as other mammalian taxa. These studies showed that hybrids are often transgressive, displaying craniofacial traits not present (or present at very low frequency) in unhybridized samples. These traits include atypical dental and sutural variation, and suggest that hybridization results in detectable signatures of breakdown in the coordination of early development. Here, analyses of size and shape (in addition to non-metric) variation in the crania, as well as postcranial variation, are presented. Mouse samples include Mus musculus subspecies (N=150), as well as M. spretus (N=50), and various first generation (F1), second generation (F2), and backcrossed (B1; B2) hybrids. Baboon samples are drawn from pedigreed baboon crania (N=985) from the Southwest National Primate Research Center in Texas, and primarily represent parental taxa and F1 crosses. Results indicate that both hybrid mice and baboons are generally heterotic, with variation that is outside of the range of the parental taxa. Individual transgressive hybrids are also identified. For the mice, these results hold across the whole phenotype, and not merely the skull, and also include transgressive coat colour/pattern traits. Beyond the F1 generation the hybrids move towards the parental phenotype in shape, however when considered in a multigenerational context the "hybrid swarm" conforms to our expectations for increased variance relative to parental groups. Macaque data, drawn from a sample of multi-generational Indian*Chinese crosses from the California National Primate Research Center, are beginning to provide information on later (e.g. 4th generation and beyond) hybrids. Currently the combined results of metric and non-metric skeletal studies offer a means for determining hybrid status in the fossil record of human evolution.

Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 demonstrates a lower back consistent with human-like lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column (“pyramidal configuration”). This contrasts with recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis (“hypolordosis”) similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2’s nearly complete middle lumbar vertebra is human-like in shape but bears large, cranially-directed transverse processes, implying powerful trunk musculature. We interpret this combina...

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.

of early hominin fossils on the continent of Africa. The fossil remains of Au. sediba were discovered in August of 2008, and the species was named in 2010 (1)* and given a provisional age of ~1.78 to 1.95 Ma (2). In 2011, detailed studies of four critical areas of anatomy of these remains were published (3-6), and a refi ned date of ~1.977 to 1.98 Ma was proposed (7). The six articles presented in full in the online edition of Science (www.sciencemag.org/site/extra/sediba), with abstracts in print (pp. 164-165), complete the initial examination of the prepared material attributed to three individuals: the holotype and paratype skeletons, commonly referred to as MH1 and MH2, and the adult isolated tibia referred to as MH4. They, along with the cumulative research published over the past 3 years, provide us with a comprehensive examination of the anatomy of a single species of early hominin. Irish et al. examine highly heritable nonmetric dental traits in Au. sediba. The species appears phylogenetically distinct from East African australopiths but close to Au. africanus, forming a southern African australopith clade. The latter shares some derived states with a clade comprising four fossil samples of the genus Homo. This result has implications for our present understanding of hominin phylogeny through the terminal Pliocene and suggests a possibility that Au. sediba, and perhaps Au. africanus, did not descend from the Au. afarensis lineage. De Ruiter et al. examine mandibular material attributable to MH2, including the previously unknown mandibular incisors and premolars of Au. sediba. As seen elsewhere in the cranium and skeleton, these mandibular remains share similarities with those of other australopiths but differ from Au. africanus in both size and shape, as well as in their ontogenetic growth trajectory. These results further support the claim that Au. sediba is taxonomically distinct from Au. africanus. Where the Au. sediba mandibles differ from those of Au. africanus, they appear most similar to those of representatives of early Homo. Churchill et al. explore the upper limb elements of Au. sediba, describing the most complete and undistorted humerus, radius, ulna, scapula, clavicle, and manubrium yet described from the early hominin record, all associated with one individual. With the exception of the hand skeleton (3), the upper limbs of the Malapa hominins are largely primitive in their morphology. Au. sediba thus shares with other australopiths an upper limb that was well suited for arboreal climbing and possibly suspension, although perhaps more so than has previously been suggested for this genus.