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Abstract
Studies of facial ontogeny in immature hominins have contributed significantly to understanding the evolution of human growth and development. The recently discovered hominin species Autralopithecus sediba is represented by a well-preserved and nearly complete facial skeleton of a juvenile (MH1) which shows a derived facial anatomy. We examined MH1 using high radiation synchrotron to interpret features of the oronasal complex pertinent to facial growth. We also analyzed bone surface microanatomy to identify and map fields of bone deposition and bone resorption, which affect the development of the facial skeleton. The oronasal anatomy (premaxilla-palate-vomer architecture) is similar to other Australopithecus species. However surface growth remodeling of the midface (nasomaxillary complex) differs markedly from Australopithecus, Paranthropus, early Homo and from KNM-WT 15000 (H. erectus/ergaster) showing a distinct distribution of vertically disposed alternating depository and resorptive fields in relation to anterior dental roots and the subnasal region. The ontogeny of the MH1 midface superficially resembles some H. sapiens in the distribution of remodeling fields. The facial growth of MH1 appears unique among early hominins representing an evolutionary modification in facial ontogeny at 1.9 my, or to changes in masticatory system loading associated with diet.
Highlights
Anatomical relations we examined MH1 using high energy CT imaging and compared its anatomy to the conditions found among other hominins
For MH1, high-resolution replicas of the face were examined in the scanning electron microscope (SEM) and surface remodeling features were mapped
MH1 shows a step-like relationship between the premaxilla and the palate and the vomer does not contact the premaxilla (Fig. 2A, Figs S3, S4). It shares these features with Au. afarensis and Au. africanus
Summary
Anatomical relations we examined MH1 using high energy (synchrotron) CT imaging and compared its anatomy to the conditions found among other hominins. Remodeling involves the coordinated deposition of bone matrix by osteoblasts and the resorption of bone by osteoclasts resulting in the balanced growth of the skull This occurs in concert with changes in the size, shape and relative positions (displacement) of individual cranial skeletal elements during postnatal growth and concomitant development and eruption of the dentition[7,8,9,10,11,12,13,14,15,16,17]. For MH1, high-resolution replicas of the face were examined in the scanning electron microscope (SEM) (see Methods) and surface remodeling features were mapped These were compared with previously described remodeling features of the skulls of diverse hominins and other primates, and with the findings of a finite elements analysis of incisor biting in a modern human to assess potential mechanical signals for remodeling activity
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