Human/Gorilla Split at Eight MYA?

Scientific American is running an article, which details work by Gen Suwa and colleagues, in the Afar Triangle, where nine gorilla-sized teeth were found in 2007 that have now been securely dated to around eight million years ago.  The researchers named the species Chororopithecus abyssinicus.  Charles Choi writes: 

The age and location of these fossils strengthen the view that the human and the modern ape lines originated in Africa and not Asia, the researchers said.

"Until now, no mammalian fossils south of the Sahara have been securely dated to 8 million to 9 million years ago," Suwa said. "Any and all fossils from this crucial time period of Africa would help unravel the story of human origins and emergence. These are the first such fossils."

In addition, until recently, "most scientists, especially geneticists, thought that the human-chimp split was as recent as 5 million years ago, and that the human-gorilla split was only about 7 million to 8 million years ago," Suwa said. "This contradicted the fossil record. For example, fossils thought to be on the human side of the split such as Ardipithecus kadabba from Ethiopia and Sahelanthropus from Chad were 6 million years old — or, in the case of the Chad fossil, perhaps 7 million years old."

The new findings suggest that Chororapithecus is 8 million years old, so "the actual gorilla-human split must then have been up to several million years before that," Suwa said.

More pieces to the puzzle. The other mystery, of course, is when the last common ancestor of humans and chimpanzees lived.

New Study: Ardipithecus ramidus Derived In Human Direction

According to Bill Kimbel and colleagues, the skull of Ardipithecus ramidus shows tell-tale signs of being derived in the human direction away from great apes.  From Science Daily:

White's field-research team has been recovering fossil remains of Ardipithecus ramidus in the Middle Awash research area, Ethiopia since the 1990s. The most recent study of the Ardi skull, led by Suwa, was published in Science in 2009, whose work (with the Middle Awash team) first revealed humanlike aspects of its base. Kimbel co-leads the team that recovered the earliest known Australopithecus skulls from the Hadar site, home of the "Lucy" skeleton, in Ethiopia.

"Given the very tiny size of the Ardi skull, the similarity of its cranial base to a human's is astonishing," says Kimbel.

The cranial base is a valuable resource for studying phylogenetic, or natural evolutionary relationships, because its anatomical complexity and association with the brain, posture and chewing system have provided numerous opportunities for adaptive evolution over time. The human cranial base, accordingly, differs profoundly from that of apes and other primates.

In humans, the structures marking the articulation of the spine with the skull are more forwardly located than in apes, where the base is shorter from front to back and the openings on each side for passage of blood vessels and nerves are more widely separated.

Given that the post-cranial remains from Ardipithecus suggest facultative bipedalism, this is not so surprising. If you are going to walk upright at all, you need to be able to see where you are going. This information, in conjunction with the new appraisal of the Orrorin tugenensis remains strongly suggests that, while Orrorin was at or near the junction of the last common ancestor, Ardipithecus, at 1.6 million years later, is quite a bit beyond it. It also reinforces what a terrible model the modern apes are for early human morphology.