CHICAGO -- A skull and jawbones recently found in China is the oldest well-preserved primate fossil ever discovered – as well as the best evidence of the presence of early primates in Asia. But the fossil raises the tantalizing possibility that remote human ancestors may have originated in Asia and stirs up debate about the nature of early primates.
In the words of Robert D. Martin, Provost and Vice President of Academic Affairs at Chicago's Field Museum, "It was once thought that primates originated in North America because that's where the earliest fossils were found initially; but we should be more open-minded. We still do not know the area of origin of the primate lineage that eventually led to humans, and this new find firmly brings Asia into the picture."
Xijun Ni and colleagues describe the fossil as Teilhardina asiatica, a new species of a genus first recognized from Belgium, in the Jan. 1, 2004, issue of Nature. At 28 grams, T. asiatica is smaller than any modern primate, and its size and sharp tooth cusps indicate that it was an insect-eater.
But a "News & Views" commentary in the same issue of Nature by Dr. Martin disagrees with part of the authors' interpretation of their new find.
Based on T. asiatica's small eye sockets relative to skull length, Ni and colleagues maintain that the small predator was diurnal (active during the day). Dr. Martin, on the other hand, says there is no compelling evidence from the fossil to shake the traditional belief that the common ancestor of primates, and early representatives such as members of the genus Teilhardina, were nocturnal (active at night).
"I disagree with the authors on both statistical and biological grounds," Dr. Martin says. "They excluded significant data in their analysis, and they did not adequately account for certain biological features, including the very large opening on the snout for the nerve connecting with the whiskers, which are best developed in nocturnal mammals."
The earliest known undoubted primate fossils are about 55-million-years old from sites in North America, Europe – and now Asia. Scientists had previously classified six of them in the genus Teilhardina. Ni adds T. asiatica to that group, which might therefore be thought to have dispersed throughout the northern continents.
Dr. Martin agrees that the new fossil belongs to the genus Teilhardina, but he argues that only it and T. belgica, found in Europe, belong there because of their shared traits. "The remaining five species previously identified as Teilhardina must, in fact, be from a quite separate genus," he said. "And this means Teilhardina was restricted to Europe and Asia and probably did not disperse all the way to what is now North America."
Dr. Martin's views have wider implications for biogeography, as well. Until recently, scientists believed that direct migration of primates between Asia and Europe around 55 million years ago would not have been possible due to a transcontinental marine barrier that ran from north to south down the middle of Eurasia at the time. Now, the presence of closely related Teilhardina species in China and Belgium adds to mounting evidence that primates and other mammals were able to migrate directly between Europe and Asia 55 million years ago.
In any event, Dr. Martin hails the new fossil as a very significant find. "It provides crucial new information about early primates in Asia that will help us understand the earliest beginnings of the branch that eventually led to human evolution," he said.