Functional biology of the Homo erectus axial skeleton from Dmanisi, Georgia

A new partial skeleton of Homo erectus attributed to the D2700 cranium was recently discovered at the site of Dmanisi, Georgia. Two cervical, two thoracic, and one lumbar vertebra are among these remains, and are also attributed to this individual. The vertebrae represent the oldest known vertebral series for this taxon, and are the oldest known outside of Africa. Because elements from each spinal region are represented, including never before seen cervical elements for this species, these fossils provide an important look at the axial skeleton of Homo erectus. The fossils were compared 2257 individual vertebrae from modern humans, chimpanzees, gorillas and fossil hominids to assess the morphological and functional structure of the Dmanisi vertebrae and associated spinal cord. Although the vertebrae correlate with a stature of only 1.39 meters (4&feet; 7&inches;), the Dmanisi vertebrae reveal key changes relative to earlier small-bodied hominids, with an anatomy for efficient long-range travel and an increased ability to bear compressive loads. Hominid range expansion beyond the African continent is, therefore, associated with not only a shift in subsistence pattern, but also with development of the ability to travel long distances with children (both in utero and in infancy). Both raw and relative values reveal that the Dmanisi spinal cord in all vertebral regions would have been fully modern in its shape and size. This contrasts with previous studies suggesting that brain evolution outpaced spinal cord evolution in the hominid lineage. The anomalous Nariokotome Homo erectus vertebrae appear to reflect pathology related to infant malnutrition, explaining why its vertebral canals and associated spinal cord size small, approximating australopithecine and chimpanzee values. These results imply that early Homo erectus departed from the ancestral continent with a postcranial neurological substrate affording high potential for throwing projectiles accurately, and for highly coordinated manual tasks, relative to their australopithecine predecessors. Moreover, this study shows that Homo erectus would have had no postcranial neuromuscular restrictions on its ability to control respiration, and, as such, possessed a fully human postcranial anatomy associated with control and coordination of respiratory muscles for spoken language