Friday, October 02, 2009

Ardipithecus ramidus: The Game Has Changed!

Wired (as well as a bunch of other sources) has a new article on the Ardipithecus ramidus find that has been analyzed. This find will change models of early human origins, for which there are actually more models than fossils. Don't misread that statement; there are plenty of fossils to reconstruct big chunks of our past but there are also some areas, particularly the early years, that are still sketchy. The article states:

“This is a landmark,” said Dean Falk, a University of Florida evolutionary anthropologist who reviewed the findings. “The field will go into a frenzy.”

Falk’s assessment was echoed by paleontologists around the world, who have waited for 15 years since a handful of 4.4 million-year-old fossils, belonging to an unknown hominid species, were found in sediments along the Awash River in Ethiopia.

Even then, the fossils were clearly special. The name of the species, chosen by paleontologist discoverers Tim White, Gen Suwa and Berhane Asfaw of the Middle Awash Project, means “root ground ape” in local dialect. The fossils likely “represent a long-sought potential root species for the Hominidae,” they wrote in a 1994 Nature paper (.pdf).

Conventional wisdom is that hominids arose due to a group of Miocene apes (Kenyapithecus?) adapting to the forest/fringe environment as environmental cooling created more savannas. These early hominids then moved to the savannas permanently around 3-3.5 mya. This find suggests that the evolution of bipedal, hominid behaviour may have taken place more in a forest environment than a savanna environment. Here is a revised tree from Wired, showing Ardipithecus, which is now assumed to be the root species in the hominid lineage.

The other takeaway message here is that the split between the precursors of chimpanzees and the precursors of gorillas is further back than we thought. Ardipithecus shows extremely derived characteristics relative to chimpanzees. In the world of human palaeontology, this is huge. It clearly shows a step between the quadrupedal apes of the Miocene and the demonstratively bipedal australopithecines of the Plio-Pleistocene. Folks, this is as transitional as it gets.

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