BioEd Online

A trove of the oldest human skeletal bones outside Africa is reported in Nature this week — a find that will help researchers to improve their understanding of the biology of the 1.8-million-year-old hominins.

The work, led by researchers from the Georgian National Museum in Tbilisi, describes three-dozen fossils from the skeletons of four primitive Homo erectus individuals found in recent years at Dmanisi in Georgia, central Asia.

H. erectus is thought to have migrated across Asia after coming out of Africa, where the oldest relative of man is traced to nearly 7 million years ago. H. erectus fossils have been found from Africa across Asia as far as Indonesia. Typically there are only a few scattered fossils at one location. A single site with so many bones from so many individuals is rare. And they date back to very soon after H. erectus's exodus from Africa.

"Dmanisi is a real gift, because nothing in the world exists like this for this time," says lead author David Lordkipanidze.

"The really important point is you have multiple individuals from the same time and location," adds Tim White, a palaeoanthropologist at the University of California, Berkeley, who was not involved in the work. Together the specimens — three adults and an adolescent — present a much better picture of what the species was like as a whole than would a single skeleton. With one individual, experts note, it is difficult to determine whether a feature such as leg length is typical of the entire species or just characteristic of that one individual.

With four skeletons, you start to have a data set that you can reasonably compare with modern humans, says Alan Walker, a palaeoanthropologist at Pennsylvania State University in University Park.

Researchers are now attempting to link these fossils to three skulls, a cranium and a mandible all found previously in the same dig site.

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The Dmanisi site — which continues to yield fossils annually — was near a lava flow where the primitive humans are thought to have scavenged carcasses for meat. But H. erectus then became a victim of carnivores, with their collective bones marked by animal teeth and found in a lair-like deposit.

Lordkipanidze and his colleagues note that the skeletal fossils of shoulder, arm, spine and leg show that the individuals were small (about 50 kilograms on a frame of some 150 centimetres tall), had modern-human body-limb proportions, and legs capable of long-distance travel.

This reflects variation expected in the species, notes anatomist Owen Lovejoy of Kent State University in Ohio. It is known that H. erectus living in colder climates had shorter limbs compared with those from the hotter environs of Africa.

Even though this sample provides a good look at H. erectus in this time and place, experts caution against drawing broad conclusions about H. erectus.

As more fossils are reported in the near future, as is expected, the growing Dmanisi collection will allow researchers to describe our relatives more definitively.