Before there was Lucy, Ardi stood out, and up

The discovery provides an extraordinary glimpse into human origins, paleontologists said yesterday.

The partial skeleton of a female who lived 4.4 million years ago is the culmination of 17 years of excavation and research. Ardi - nicknamed for her species, Ardipithecus ramidus - stood about 4 feet tall, weighed 110 pounds, and was less like a chimpanzee than many scientists had expected.

Scientists hailed the work as a landmark in efforts to fill in the puzzle of human evolution, helping to illuminate how we got to be the way we are. Ardi’s bone structure, for example, contains clues about the emergence of our ability to walk on two feet. Other fossils found with Ardi shed light on her species and the environment in which they lived.

“This is a spectacular collection of fossils from an especially important ancestor; this is one of the biggest finds in the last 50 years of human evolutionary studies,’’ said Carol V. Ward, a professor of anatomy at the University of Missouri-Columbia who specializes in studying apes that lived more than 5 million years ago, and was not involved in the research. “You have an animal . . . that is quite clearly a close cousin of ours, if not an ancestor, but [from] earlier in time than most fossils ever found. It is really an outstanding opportunity and is just unparalleled.’’

Ardi comes from the largely mysterious period after the ancestors of humans and chimpanzees split more than 6 million years ago. She is discernibly more primitive than the previously discovered 3.2 million-year-old skeleton known as Lucy, the best known example of a later prehuman species, Australopithecus afarensis. Ardi’s species might even have been an ancestor of Australopithecus, scientists said.

The findings are reported in a special issue of the journal Science published today, featuring 11 papers representing the work of an international team of 47 scientists.

Ardi was discovered in a section of Ethiopia’s Afar Rift that is about 45 miles from where Lucy was discovered in 1974. Dozens of fossilized fragments of Ardi’s species were also found.

The first piece of Ardi’s hand was discovered 15 years ago, but excavating and reconstituting her skeleton - including her skull, teeth, pelvis, hands, legs, and feet - was a monumental and lengthy project that used everything from old-fashioned digging to medical imaging technology. Ardi’s fossilized remains were splintered into many pieces, as if they had been trampled by a large animal, and were very fragile, crumbling to the touch.

“The find itself is extraordinary, as were the enormous labors that went into the reconstruction of a skeleton shattered almost beyond repair, and particularly the skull,’’ David Pilbeam, curator of paleoanthropology at the Peabody Museum of Archaeology and Ethnology at Harvard University, wrote in an e-mail.

What that work revealed is a study in contrasts. Ardi’s pelvis is a mosaic: Some features are specialized for climbing, but some indicate that she would have walked upright as well, a hallmark of the human lineage. Her hands and feet are like those of primitive extinct apes, with a grasping toe, and, unlike humans and Australopithecus, no arch in the foot, meaning she would not have been very efficient at walking on two feet. There is no evidence that she walked on her knuckles, like chimpanzees.

“A lot of people were happy to hypothesize that as you went back, into that first half of human evolution since the last common ancestor, as you found these fossils they’d be increasingly chimpanzee-like,’’ said Tim D. White, a paleontologist at the University of California, Berkeley, and a leader of the research team. “We have something getting pretty close to it in time, and it turns out it doesn’t look chimpanzee-like; it’s an unexpected combination of characteristics, some of which are new in evolution and put this pretty firmly on our side of the family tree, and some others that are very primitive.’’

Ardi’s remains were sandwiched between two layers of volcanic rock, which were used to date the sample. Scientists also recovered fragments of her woodland habitat, which contained everything from fig trees and snails to elephants and porcupines.

The fact that Ardi lived in a wooded setting was important, scientists said, because it counters the popular notion that the ability to walk on two legs started to evolve because human ancestors moved to the savannah and was a result of the new habitat.

Donald Johanson, founding director of the Institute of Human Origins at Arizona State University and the scientist who discovered Lucy, said the new find was likely to spark vigorous debate as outside scientists try to understand Ardi’s strange mixture of traits and how much she walked on two feet.

“I think it’s a significant discovery . . . and will generate an enormous amount of controversy,’’ said Johanson. “I think it’s very important to say that this supports the long-held idea that we did not evolve from things that look like modern apes.’’

Carolyn Y. Johnson can be reached at cjohnson@globe.com.