![]() ![]() (2009b) palmigrade quadrupedality only took place in the trees on the ground, they claim, Ardipithecus engaged in facultative bipedalism. Ardipithecus ramidus has an interesting mosaic of features, which its authors interpret as evidence of palmigrade quadrupedality grading into facultative bipedalism. ![]() The controversy surrounding Ardipithecus ramidus is mostly to do with its putative bipedal locomotor capabilities, one of the features often used to distinguish early humans from early chimpanzees. The collection of fossils attributed to the third fossil species, Ardipithecus ramidus, for example, is more complete than that of either Sahelanthropus or Orrorin, but its status is even more vigorously disputed. The incompleteness of these fossils is a major factor in their resistance to categorization but it is not the only reason. Problematically, it would be rash to assume that thick tooth enamel is exclusive to humans and, more importantly, CT scan technology hasn't actually managed to capture a distinct enough image of the femoral neck to comment on cortical bone morphology (Wood, 2005). Supposedly, locomotor mode leaves signature patterns of differential distribution of cortical bone in the femoral neck, with habitual bipeds exhibiting thickening of such bone at the top and bottom of the neck. ![]() (2001) claimed that these fragments belong on the human lineage because of the thick enamel covering the molar and premolar teeth and the internal morphology of the femoral neck. The picture doesn't get much clearer with the introduction of 6 Ma Orrorin tugenensis, that includes a set of molars and a femoral fragment from the Tugen Hills of northern Kenya (Senut et al., 2001). ![]()
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