The discovery of four fossil skeletons of early human ancestors in Georgia, the former Soviet republic, has given scientists a revealing glimpse of a species in transition, primitive in its skull and upper body but with more advanced spines and lower limbs for greater mobility.

The findings, being reported today in the journal Nature, are considered a significant step toward understanding who were some of the first ancestors to migrate out of Africa some 1.8 million years ago. They may also yield insights into the first members of the human genus, Homo.

Until now, scientists had found only the skulls of small-brain individuals at the Georgian site of Dmanisi. They said the new evidence apparently showed the anatomical capability of this extinct population for long-distance migrations.

“We still don’t know exactly what we have got here,” David O. Lordkipanidze, the excavation leader, said Monday in an interview on a visit to New York. “We’re only beginning to describe the nature of the early Dmanisi population.”