The Great Ida Debate

Guatam Naik wrote:

In what could prove to be a landmark discovery, a leading paleontologist said scientists have dug up the 47 million-year-old fossil of an ancient primate whose features suggest it could be the common ancestor of all later monkeys, apes and humans.

Anthropologists have long believed that humans evolved from ancient ape-like ancestors. Some 50 million years ago, two ape-like groups walked the Earth. One is known as the tarsidae, a precursor of the tarsier, a tiny, large-eyed creature that lives in Asia. Another group is known as the adapidae, a precursor of today's lemurs in Madagascar.

Based on previously limited fossil evidence, one big debate had been whether the tarsidae or adapidae group gave rise to monkeys, apes and humans. The latest discovery bolsters the less common position that our ancient ape-like ancestor was an adapid, the believed precursor of lemurs.

Philip Gingerich, president-elect of the Paleontological Society in the U.S., has co-written a paper that will detail next week the latest fossil discovery in Public Library of Science, a peer-reviewed, online journal.

"This discovery brings a forgotten group into focus as a possible ancestor of higher primates," Mr. Gingerich, a professor of paleontology at the University of Michigan, said in an interview.

The discovery has little bearing on a separate paleontological debate centering on the identity of a common ancestor of chimps and humans, which could have lived about six million years ago and still hasn't been found. That gap in the evolution story is colloquially referred to as the "missing link" controversy. In reality, though, all gaps in the fossil record are technically "missing links" until filled in, and many scientists say the term is meaningless.

Nonetheless, the latest fossil find is likely to ignite further the debate between evolutionists who draw conclusions based on a limited fossil record, and creationists who don't believe that humans, monkeys and apes evolved from a common ancestor.

Scientists won't necessarily agree about the details either. "Lemur advocates will be delighted, but tarsier advocates will be underwhelmed" by the new evidence, says Tim White, a paleontologist at the University of California, Berkeley. "The debate will persist."

The skeleton will be unveiled at New York City's American Museum of Natural History next Tuesday by Mayor Michael Bloomberg and an international team involved in the discovery.

According to Prof. Gingerich, the fossilized remains are of a young female adapid. The skeleton was unearthed by collectors about two years ago and has been kept tightly under wraps since then, in an unusual feat of scientific secrecy.

Prof. Gingerich said he had twice examined the adapid skeleton, which was "a complete, spectacular fossil." The completeness of the preserved skeleton is crucial, because most previously found fossils of ancient primates were small finds, such as teeth and jawbones.

It was found in the Messel Shale Pit, a disused quarry near Frankfurt, Germany. The pit has long been a World Heritage Site and is the source of a number of well-preserved fossils from the middle Eocene epoch, some 50 million years ago.

Prof. Gingerich said several scientists, including Jorn Hurum of Norway's National History Museum, had inspected the fossil with computer tomography scanning, a sophisticated X-ray technique that can provide detailed, cross-sectional views. Dr. Hurum declined to comment.

Although the creature looks like a lemur, there are some distinctive physical differences. Lemurs have a tooth comb (a tooth modified to help groom fur); a grooming claw; and a wet nose. Dr. Gingerich said that the adapid skeleton has neither a grooming claw nor a tooth comb. "We can't say whether it had a wet nose or not," he noted.

Since the fossilized creature found in Germany didn't have features like a tooth comb or grooming claw, it could be argued that it gave rise to monkeys, apes and humans, which don't have these features either.