"All of a sudden there is more evidence, and when you have more evidence ideas can change," said Ciochon, who details his change of heart in an essay in tomorrow's issue of the journal Nature.
Archaeologist Richard Potts noted that if anyone's qualified to change the conclusions in this case, it's Russell Ciochon.
"Russell has probably seen more isolated teeth of primates from this time period than anyone else," said Potts, director of the Human Origins Program at the Smithsonian Institution in Washington, D.C.
Still, it's unclear to Ciochon, or anyone else, what such mystery apes were like.
Chinese anthropologist Wang Wei from the Guangxi museum is to lead an effort to evaluate, and reevaluate, unidentified primate fossils from around southeastern Asia. The results, it's hoped, will help fill in the ape family tree for the region.
Ciochon's new theory is based on more than a new anatomical analysis.
The mystery-ape fossils were found in what was once a massive subtropical forest. The tooth-yielding caves, for example, house fossils of forest animals such as the elephant-like Stegodon, a prehistoric panda, and the extinct giant ape Gigantopithecus as well as ancestors of orangutans and gibbons.
Early humans, Ciochon hypothesizes, probably could not, or would not, have lived in such a place.
"Through a long history of analyzing fossil sites in Africa where the genus Homo is found, we know that these early humans were living in grassland or savanna-fringe environments," he said.
"If early humans lived in these more open environments in Africa, why would they inhabit a subtropical forest in Asia?"
But the Smithsonian's Potts noted that the prehistoric environment was dynamic and highly variable, and he cautioned against black-and-white designations like "forest" or "grassland."
A typical Pleistocene landscape in the region would likely have been more mixed, including open areas around a swamp or lake, bushy vegetation, and a surrounding highland forest, said Potts, citing recent discoveries of fossil pollen, spores, and sediment at Pleistocene sites.
"I think," Potts said, "that we shouldn't let the environment dictate the taxonomy."
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