Australopithecus sediba

The phylogenetic relationships of several hominin species remain controversial. Two methodological issues contribute to the uncertainty—use of partial, inconsistent datasets and reliance on phylogenetic methods that are ill-suited to testing competing hypotheses. Here, we report a study designed to overcome these issues. We first compiled a supermatrix of craniodental characters for all widely accepted hominin species. We then took advantage of recently developed Bayesian methods for building trees of serially sampled tips to test among hypotheses that have been put forward in three of the most important current debates in hominin phylogenetics—the relationship between Australopithecus sediba and Homo, the taxonomic status of the Dmanisi hominins, and the place of the so-called hobbit fossils
from Flores, Indonesia, in the hominin tree. Based on our results, several published hypotheses can be statistically rejected. For example, the data do not support the claim that Dmanisi hominins and all other early Homo specimens represent a single species, nor that the hobbit fossils are the remains of small-bodied modern humans, one of whom had Down syndrome. More broadly, our study provides a new baseline dataset for future work on hominin phylogeny and illustrates the promise of Bayesian approaches for understanding hominin phylogenetic relationships.

Understanding the manual abilities of fossil hominins has been a focus of palaeoanthropological research for decades. Of interest are the morphological characteristics of the thumb due to its fundamental role in manipulation, particularly that of the trapeziometacarpal joint. Considerably less attention has been given to the thumb metacarpophalangeal (MCP) joint, which plays a role in stabilizing the thumb during forceful grasps and precision pinching. In this study we use a three-dimensional geometric morpho-metric approach to quantify the shape of the first metacarpal head in extant hominids (Homo, Pan, Gorilla and Pongo) and six fossil hominin species (Homo neanderthalensis Tabun C1 and La Chappelle-aux-Saints, Homo naledi U.W. 101-1282, Australopithecus sediba MH2, Paranthropus robustus/early Homo SK84, Aus-tralopithecus africanus StW 418, Australopithecus afarensis A.L. 333w-39), with the aims of identifying shapes that may be correlated with human-like forceful opposition and determining if similar morphologies are present in fossil hominins. Results show that humans differ from extant great apes by having a distally flatter articular surface, larger epicondyle surface area, and a larger radial palmar condyle. We suggest that this suite of features is correlated with a lower range of motion at the MCP joint, which would enhance the thumbs ability to resist the elevated loads associated with the forceful precision grips typical of humans. Great ape genera are each differentiated by distinctive morphological features, each of which is consistently correlated with the predicted biomechanical demands of their particular locomotor and/or manipulatory habits. Neanderthals and U.W. 101-1282 fall within the modern human range of variation, StW 418, SK 84 and U.W. 88-119 fall in between humans and great apes, and A.L. 333w-39 falls within Pan variation. These results agree with those of traditional linear analyses while providing a more comprehensive quantitative basis from which to interpret the hand functional morphology of extinct hominins.

Australopithecus sediba is known from two partial skeletons, Malapa Hominins 1 and 2 (MH1 and MH2), a juvenile
male and an adult female, respectively. Forty-eight elements of the axial skeleton, including vertebrae, ribs, a
sternum, and a sacrum, are known from MH1 and MH2. Here, we describe these ~2.0 Ma fossils and provide raw
data and plots of standardized measurements. We revisit the serial positions of the previously described vertebrae
and ribs proposed in their initial announcements and provide revised identifications. Additionally, we include
in our descriptions and analyses new axial material. Finally, we also test the hypothesis that multiple species are
represented in the MH1 and MH2 material and specifically that MH1’s lumbar vertebrae belong to a member of
the genus Homo, whereas those of MH2 belong to Australopithecus. We do not find support for this hypothesis, and
instead attribute differences between MH1 and MH2 to their age difference and incomplete growth of the vertebral
body in juvenile MH1.

We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported from the type specimen of the extinct hominin Australopithecus sediba from Malapa, South Africa, dated to 1.98 million years ago. The affected individual was male and developmentally equivalent to a human child of 12 to 13 years of age. A penetrating lytic lesion affected the sixth thoracic vertebra. The lesion was macroscopically evaluated and internally imaged through phase-contrast X-ray synchrotron microtomography. A comprehensive differential diagnosis was undertaken based on gross- and micro-morphology of the lesion, leading to a probable diagnosis of osteoid osteoma. These neoplasms are solitary, benign, osteoid and bone-forming tumours, formed from well-vascularised connective tissue within which there is active production of osteoid and woven bone. Tumours of any kind are rare in archaeological populations, and are all but unknown in the hominin record, highlighting the importance of this discovery. The presence of this disease at Malapa predates the earliest evidence of malignant neoplasia in the hominin fossil record by perhaps 200 000 years.

We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported from the type specimen of the extinct hominin Australopithecus sediba from Malapa, South Africa, dated to 1.98 million years ago. The affected individual was male and developmentally equivalent to a human child of 12 to 13 years of age. A penetrating lytic lesion affected the sixth thoracic vertebra. The lesion was macroscopically evaluated and internally imaged through phase-contrast X-ray synchrotron microtomography. A comprehensive differential diagnosis was undertaken based on gross-and micro-morphology of the lesion, leading to a probable diagnosis of osteoid osteoma. These neoplasms are solitary, benign, osteoid and bone-forming tumours, formed from well-vascularised connective tissue within which there is active production of osteoid and woven bone. Tumours of any kind are rare in archaeological populations, and are all but unknown in the hominin record, highlighting the importance of this discovery. The presence of this disease at Malapa predates the earliest evidence of malignant neoplasia in the hominin fossil record by perhaps 200 000 years.

Two partial vertebral columns of Australopithecus sediba grant insight into aspects of early hominin spinal mobility, lumbar curvature, vertebral formula, and transitional vertebra position. Au. sediba likely possessed five non-rib-bearing lumbar vertebrae and five sacral elements, the same configuration that occurs modally in modern humans. This finding contrasts with other interpretations of early hominin regional vertebral numbers. Importantly, the transitional vertebra is distinct from and above the last rib-bearing vertebra in Au. sediba, resulting in a functionally longer lower back. This configuration, along with a strongly wedged last lumbar vertebra and other indicators of lordotic posture, would have contributed to a highly flexible spine that is derived compared with earlier members of the genus Australopithecus and similar to that of the Nariokotome Homo erectus skeleton.