INFERENCES CONCERNING BIPEDAL LOCOMOTION FROM THE INTERNAL STRUCTURE OF THE BAR 1002’00 AND BAR 1003’00 FEMORAL FRAGEMENTS

Open Access
Author:
Kuperavage, Adam John
Graduate Program:
Kinesiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 20, 2009
Committee Members:
  • Robert Barry Eckhardt, Dissertation Advisor
  • Robert Barry Eckhardt, Committee Chair
  • John Henry Challis, Committee Chair
  • Stephen Jacob Piazza, Committee Member
  • Henry Joseph Sommer Iii, Committee Member
Keywords:
  • second moment of area
  • cortical bone distribution
  • moment coefficient of area
  • Orrorin tugenensis
Abstract:
The fossil evidence pertinent to the reconstructing the origins of human bipedal locomotion generally is sparse and fragmentary. Prior to four million years ago the record is nearly nonexistent. Among the very limited earlier remains are those from several sites in the Tugen Hills of Kenya, dated to approximately six million years ago. These remains have been assigned by their discoverers to the taxon Orrorin tugenensis. The hypodigm of Orrorin tugenensis includes two partial proximal femora, specimens BAR 1002’00 and BAR 1003’00. The external and internal morphological features of these specimens have been described multiple times by their discoverers and others over the last eight years. Studies of the internal properties of these specimens are extended here. These additional studies include measurement of the geometric cross-sectional properties in the femoral diaphyses of BAR 1002’00 and BAR 1003’00, and comparison of these data with those of several samples of earlier hominids and extant humans; measurement of the cortical bone distributions in the femoral neck using moment coefficients of skewness, and comparison of these to samples of chimpanzees and extant humans; and measurement of the calcar femorale in BAR 1003’00, with comparisons to chimpanzee and human specimens. It was found that total cross-sectional area is markedly smaller for BAR 1002’00 and BAR 1003’00 than for either early or extant hominid proximal femora. The percent cortical areas of the two Kenyan fossil femora are comparable to other fossil hominids. With regard to moment coefficients of skewness, BAR 1002’00 exhibits cortical bone distributions more similar to chimpanzees than to humans. The calcar femorale was found to be present in chimpanzees as well as in humans. BAR 1003’00 appears to have a calcar femorale more similar to that of extant humans than to chimpanzees. All of these findings, taken together, provide evidence bearing on the status of Orrorin tugenensis as a basal hominid.