By John Noble Wilford
Another species has been added to the family tree of early human ancestors -- and to controversies over how straight or tangled were the branches of that tree.
Long before Homo erectus, Australopithecus afarensis (``Lucy,'' more than 3 million years ago) and several other distant kin, scientists are reporting today, there lived a primitive hominid species in what is now Ethiopia about 5.5 million to 5.8 million years ago.
That would make the newly recognized species one of the earliest known human ancestors, perhaps one of the first to emerge after the chimpanzee and human lineages diverged from a common ancestor 6 million to 8 million years ago.
The timing of the fateful split has been determined by molecular biological research, and in recent years fossil hunters have found traces of what those earliest hominids, human ancestors and their close relatives, might have been like.
When the first fossil bones and teeth of this hominid were described three years ago, paleoanthropologists tentatively identified it as a more apelike subspecies that they named Ardipithecus ramidus kadabba. The original ramidus species had been found in 1994 in 4.4 million-year-old sediments, also in Ethiopia.
But with more discoveries and closer study, especially of the teeth, the scientists decided that the kadabba fossils from five individuals were distinctive enough to qualify as a separate species: Ardipithecus kadabba. In that case, the scientists added, kadabba was not a subspecies, but probably the direct ancestor of ramidus. But there were too few skeletal bones to learn much about the size and other aspects of kadabba.
The description and interpretation of the new hominid species appears in today's issue of the journal Science. The authors of the report are Yohannes Haile-Selassie of the Cleveland Museum of Natural History, Gen Suwa of the University of Tokyo and Tim D. White of the University of California-Berkeley.
The kadabba fossils were found in the Middle Awash valley about 180 miles northeast of Addis Ababa, the Ethiopian capital.
Other scientists familiar with the research, but not involved
in it, said they agreed or at least were inclined to agree with
the authors' designation of a separate species for the fossils.
But they were not so sure about the authors' proposal that the
fossils were so similar to those of two other recently discovered
early species that all three species may have belonged to a single
genus of closely related hominids.