Tuesday, December 10, 2013

Orrorin tugenensis: As Close to the Last Common Ancestor As We Have Gotten?

Based on work by SUNY Stoney Brook, it has been learned that the femur of Orrorin tugenensis, the six-million year-old presumed hominin, also called the "millenium man," has a mix of traits that align it with not just early hominins but late Miocene apes.  Science Daily reports:
According to Dr. Alm├ęcija, their study for the first time compared the six-million-year-old Millenium Man femur (called BAR 1002'00) using state-of-the-art morphometric techniques to not only other available hominin fossils but also great apes, hylobatids (ie, gibbons and siamangs), and most importantly to fossil apes that lived in the Miocene. The analysis included more than 400 specimens.

"We discovered that
Orrorin's femur is surprisingly 'intermediate' in both age and anatomy between quadrupedal Miocene apes and bipedal early human ancestors," said Dr. Alm├ęcija. "Our paper provides quantitative results of the Orrorin femur as a unique mosaic and stresses the need to incorporate fossil apes into future analyses and discussions dealing with the evolution of human bipedalism, an investigation that should stop considering chimpanzees as default living 'starting point' models."
As the authors note, this is not so different from what was concluded about the gait of Ardipithecus ramidus and that the examination of that hominin led to the idea that, perhaps, modern apes are poor models for early hominin morphology and that the modern apes diverged from the last common ancestor (LCA) in entirely different directions. It is exciting to get to a point where there are obviously transitional characters between hominins and non-hominins. 

The other thing that is quite striking is that there is no obvious dividing line between being a quadruped and a biped and that the transition took some time and was gradual.  Don Johanson, in Lucy: The Beginnings of Humankind, word:
You don’t gradually go from being a quadruped to being a biped. What would the intermediate stage be–a triped? I’ve never seen one of these.
It appears that he may have been wrong, at least about the gradual part.

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