NewsMax.com Wires
Thursday, July 12, 2001

This ancestor, which walked on two legs, lived between 5.2 million and 5.8 million years ago in a life-defying environment of exploding volcanoes, jarring earthquakes and sizzling lava showers, the investigators from Ethiopia and the United States said in the British journal Nature.

Although a French team recently excavated the remains of a creature that inhabited the planet even earlier than that, some 6 million years ago, the evidence is too cursory to place it on the evolutionary branch that gave rise to today's men and women, scientists told United Press International.

The new find is one for the books in several respects. It was made by the same graduate student whose meticulous attention to detail brought forth a prize specimen in the 1994 expedition. It promises to require revisions of long-held views of early human ancestry. It marks a milestone in African paleoanthropology.

The fragmentary fossils, which appear to be family members of the species discovered in 1994 named Ardipithicus ramidus and dated to 4.4 million years ago, go back to nearly the time when human ancestors are thought to have split off from the chimpanzees in the first major turn on the road to modern Homo sapiens.

"Together, these finds make it the longest record for human evolution on earth," the discoverer, Yohannes Haile-Selassie, a graduate student at the University of California, Berkeley, told UPI from the Ethiopian capital of Addis Ababa, where he later discussed his findings at a news conference.

"The hominid tree [relating to members of the human family] was never very bushy compared to rats or monkeys or many other mammals, and the new fossils lie at the very base of that sparse tree," UC Berkeley paleoanthropologist Tim White, who led the 1994 expedition, told UPI.

"The exciting thing is that we have now worked our way back to the very time of origin of the initiation of the phyletic line that would eventually lead to the evolution of cognitive life," said C. Owen Lovejoy, professor of anthropology at Kent State University in Kent, Ohio, who was not involved in the project but has seen the specimens.

"We essentially have almost a complete roadmap now - there are many towns and villages that we need to add to the map and describe - but it's now almost a complete route from beginning to end," Lovejoy said.

The teeth, jawbone, hand, arm, collar bones and an especially telling toe bone - collected between December 1997 and this past January - have been designated, for now, as belonging to a subspecies of Ardipithicus ramidus dubbed "kadabba."

"Its dentition is that of a hominid, its toe bone is like that of a bipedal animal," said study author Haile-Selassie, who continues to study the fossils at the National Museum of Ethiopia in Addis Ababa.

"It's definitely a hominid and proves that the earlier 4.4-mllion-year-old Ardipithecus ramidus was a hominid, not an ape." While cautious in his classification of the fossils, he thinks with further finds and studies, "it will be elevated to a species rank of its own, in which case it would become Ardipithecus kadabba." The findings call for a reassessment of how humans view their earliest ancestors, scientists said.

"Haile-Selassie's discoveries provide us with a new minimal age estimate of the chimp-human split," said Gen Suwa of the University of Tokyo, who got a chance to view the fossils in the museum laboratory in Addis Ababa.

"Molecular based divergence estimates are calculated under various assumptions, and henceforth we can never be sure. The final say will have to come from the fossils, such as the ones being announced by Haile-Selassie." The findings bring scientists closer than ever to the long-elusive common ancestor.

"Haile-Selassie's fossils show that we are banging on the door now," Suwa told UPI.

The 11 fossils from at least five chimpanzee-sized individuals include samples of two critically important features that define hominids: feet and teeth.

"These canine teeth are not of humans, but no chimp has canine teeth like that either," White said. "This argues that these fossils are not from the common ancestor of both chimps and humans, but from very early in our evolution, shortly after our ancestors parted company and before our canines fully reduced."

Equally telling is the slanted surface at the rear joint of the prehistoric toe bone. This anatomy, characteristic of A. ramidus and later hominids that walked on two legs, is caused by "toeing-off," or propelling forward by leaving the front part of the foot on the ground and lifting the heel. The feature is absent in chimps and other apes that walk on the outside of their feet.

"These fossils are filling out the hominid family album all the way back to the split with the ancestors of the African apes," Lovejoy said. "It's as exciting to an anthropologist as a glimpse into a moment after the big bang would be for a physicist."

It may yet turn out that the fossils found in Kenya last February and dated at six million years by a team of French paleoanthropologists are of the earliest hominid. At this point, however, more samples and studies are needed before scientists can determine whether the creature, named Orrorin tugenensis, was the earliest human ancestor, the oldest chimpanzee or the long-sought common ancestor.

A second Nature article, authored by geologist Giday WoldeGabriel of Los Alamos National Laboratory in Los Alamos, N.M., and co-written by Haile-Selassie, White and others, describes the geology and environment of the region Ardipithecus called home 6 million years ago.

Today's harsh desert was then even less hospitable, a well-defined rift valley ripped by intense earth movements, shaken by volcanoes erupting from major factures and individual centers - some of them underwater in the ancient lakes that dotted the region - and showered by thick, steaming volcanic ash.

"It is hard to imagine that life would go on normally under such hostile environmental conditions," WoldeGabriel said. "Ardipithecus and the other animals inhabiting the area were real survivors." There was occasional reprieve.

"The effects of volcanism were dramatic in the lifetime of individual organisms, but as conditions returned to normal, plants and animals came back each time as seen by their fossils interbedded between the volcanic layers that were produced by eruptions separated by tens or hundreds of thousands of years," WoldeGabriel, who accompanied Haile-Selassie on week-long forays into the scorching, moisture-less area, told UPI.

The evidence indicates the ancient hominid lived in a wet, wooded habitat far different from the savanna environs long envisioned as the birthplace of human ancestors. Chemical analysis of ancient soils that entombed the fossils support this conclusion.

"The expectation was that we would find hominids in savanna grassland sites that date back to about 8 million years ago," said Stanley Ambrose, associate professor of anthropology at the University of Illinois, Urbana-Champaign, who conducted the chemical tests. "That hasn't happened. All older hominids have been found in forested environments."

The findings throw cold water on theories that ascribe the origin of hominids to global climatic change or as an adaptation to conditions of a savanna habitat, scientists said. Instead, they suggest the earliest hominids came from wet and wooded homes and did not venture into more open grassland until after 4.4 million years ago, long after hominids and chimpanzees split from their common ancestor.

"This revelation falsifies a host of hypotheses set forth to explain bipedality - most of them dependent upon it being a consequence of the shift from forest to savanna," Lovejoy said. "We need to completely reassess current theories about why humans diverged from the ancestors of other apes, and what evolutionary forces were at play when this occurred."

The publication of the two papers is also significant because both lead authors are Ethiopian, marking a "major milestone" for African researchers in the field, White said.

"These two local scholars have joined the international scientific community at the highest level. This is a huge development in African paleoanthropology and a welcome change in the conduct of this science," he said.

Guided by satellite imagery that targeted promising sedimentary outcrops, the fossil hunters set out on their challenging mission.

"We had to walk for two hours to just get to the site," Haile-Selassie said.

After months of difficult, meticulous scrutiny, he got his reward on Dec. 16, 1997 - a jawbone with one molar.

"The first thing I picked up was the mandible. I had no doubt that it belonged to a hominid. It was sitting on the surface, waiting for some lucky guy to pick it up and it turned out to be me!" Haile-Selassie said. "This was a highlight of the season, the first Late Miocene hominid anybody had ever found in Ethiopia or even the world. That night we sat around the camp table with flashlights looking at the fossil and celebrating."

Their work has just begun, the scientists said.

"We are only starting to see the picture develop, and I want to work to see it fully develop so that we can understand where we came from, and why," Haile-Selassie said.

Already, the rewards have been remarkable.

"Think of it - last November hominid evolution before 4.4 million years ago was a complete mystery. Now it's July, and there are two major sets of fossils that take our knowledge back to 6 million years," White said.

"That's a giant leap for human paleontology, and perhaps even more importantly, the fact that Ethiopian scholars are responsible for these discoveries and hard at work in the field and laboratory is a wonderful indicator of what the future holds for learning more about our African origins."

Copyright 2001 by United Press International.

All rights reserved.

A product that might interest you:
Get your site on ALL the top search engines INSTANTLY!