Saturday, July 10, 2010
One, Two, Three, Many Bipeds…Bipedalism is Nothing Special
Mark my words, a paradigm shift is in the making. Let me be the first to announce it. One hundred years from now (if we survive as a species and continue to advance in our scientific knowledge of the past) paleoanthropologists will take it as a given that hominids (in the traditional sense of the term) were one of a multitude of bipedal ape lineages that emerged in the late Miocene and early Pliocene, 5-8 mya. Parallelisms are rampant in primate evolution. Many now think that the defining upper body features of extant hominoids (including gibbons, orangutans, gorillas, chimpanzees and humans) for suspensory below branch locomotion evolved in parallel. More recently, the knuckle walking terrestrial locomotor pattern of chimpanzees and gorillas has been put forth as an example of parallel evolution. Why should bipedalism be any different? If it has been as successful an adaptation as the fossil record suggests (almost all hominoid fossils found in Africa over the last 6-7 million years have been or are thought to have been bipeds) why shouldn’t bipedalism have evolved independently in several different late Miocene ape lineages? My recent posts regarding Lufengpithecus support this hypothesis. Lufengpithecus, a late Miocene ape from Yunnan in southern China, seems to possess the very same basicranial and femoral adaptations for bipedalism that have been used to assign the likes of Sahelanthropus, Orrorin and Ardipithecus to the Hominidae (s.s.). This raises an interesting conundrum. Either Lufengpithecus is an early Asian hominid (s.s.) or bipedalism was an important constituent part of the locomotor repertoire of more than one late Miocene ape lineage. Given the fact that the non-hominid Oreopithecus also had features consistent with bipedalism it is becoming ever more apparent that there may have been multiple bipedal lineages during the late Miocene and early Pliocene. Perhaps Sahelanthropus, Orrorin and Ardipithecus represent other pre-hominid bipedal lineages as well. Or, as I’ve previously suggested, perhaps adaptations for bipedalism occurred in the LCA of the Great Ape clade (including humans), the African ape clade (including humans), or the chimpanzee/human clade. No matter which of these musings proves true (if any) the possibility that there were one, two, three or many bipedal hominoid lineages during the late Miocene and early Pliocene should be taken seriously.