Dmanisi Skull 5 and the Early Humans Who Left Africa

Dmanisi did not start out as a fossil site. It is a medieval town and fortress in southern Georgia, and excavation of the medieval settlement began in 1936. Underneath those ruins lie much older Lower Paleolithic deposits, and the clue came from an unexpected animal: in 1983 a rhinoceros tooth showed that the layers beneath the town were far older than anything medieval, according to the IUGS Dmanisi Collection record. Stone tools were identified in 1984, as UNESCO's listing notes.

Then the human fossils began to appear. The first, a lower jaw catalogued as D211, came in 1991. Two partial crania followed in 1999, a large mandible in 2000, and a nearly complete skull of a young individual, Skull 3 (D2700), in 2001. Skull 4 (D3444) came in 2002, and Skull 5 in 2005. Alongside them the site has produced more jaws, loose teeth, other bones, animal fossils and stone tools.

One hill in Georgia, in other words, holds a castle town above and some of the oldest human fossils outside Africa below.

The short answer is about 1.8 million years. The layers that hold the human fossils are generally dated to about 1.77 million years ago, using three lines of evidence: magnetostratigraphy, which reads the record of Earth's magnetic field in the rock; biostratigraphy, which compares the animal fossils with those from layers of known age; and argon-argon dating of volcanic material.

A 2011 study by Ferring and colleagues in PNAS dated the earliest occupation of the site to between 1.85 and 1.78 million years ago. They based this on a known flip in Earth's magnetic field, the Olduvai-Matuyama boundary, and on dating the Masavera Basalt, a volcanic layer at the site. The skull-bearing layers are younger than those first traces of people, which is why you will see the fossils described as about 1.8 or about 1.77 million years old. An earlier 2002 Science paper on another Dmanisi skull gave about 1.75 million years.

All of these figures date the rock around the fossils rather than the bones themselves. Our story on how old bones are dated covers the general idea.

Skull 5 came together in two parts. The cranium, D4500, was recovered in 2005. Its lower jaw, D2600, had been found earlier, and when the two were fitted together they made a complete adult skull. Lordkipanidze and colleagues described it in Science in 2013, and a later paper, "Skull 5 from Dmanisi", followed in 2017.

The surprise was in the proportions. The braincase holds about 546 cubic centimeters, among the smallest known for any fossil assigned to *Homo*. Yet the face is large and strongly projecting, with big jaws and big teeth. The skull also mixes traits seen in early African *Homo* with traits seen in later *Homo erectus*.

In later *Homo* fossils, a large, projecting face is often associated with a larger braincase. Skull 5 broke that pattern. It widened the known range of how early *Homo* could look, and it blurred the neat line some scientists had drawn between fossils that look like *Homo habilis* and fossils that look like *Homo erectus*. For the modern skull, with its much larger braincase, see our human skull facts.

This is the big argument, and it is still going. The five Dmanisi crania range from about 546 to 775 cubic centimeters in braincase volume, and they differ a lot in the shape of the face and skull. Two readings of that variety compete.

In 2013 Lordkipanidze, Marcia Ponce de León, Yoel Rak, G. Philip Rightmire, Abesalom Vekua and Christoph Zollikofer argued that all five belong to a single lineage, usually placed within *Homo erectus*. Their case rested on how closely the fossils are tied together in place and time, on comparisons with the range of variation in chimpanzees, bonobos and modern humans, and on geometric-morphometric analysis, a way of measuring and comparing skull shape mathematically. They concluded that Dmanisi documents unusually wide variation inside one early *Homo* population, and that similar variation may have been underestimated among early *Homo* fossils in Africa.

Not everyone agreed. In a 2014 Science comment, Jeffrey Schwartz, Ian Tattersall and Zhang Chi argued that the teeth, jaws and skulls show more than one kind of hominin. They supported keeping the name *Homo georgicus* for at least part of the sample.

Later studies have split. Some quantitative analyses, such as the work titled "More Than One Species? Variation in Dmanisi Crania", did not reject the single-species idea, while later dental work has again argued for more than one lineage. A discussion of the Dmanisi mandibles adds to the jaw side of the debate. The species question remains open. For more on the species most often named here, see our story on the Homo erectus skull.

It might, but it cannot prove it. Skull 4, the cranium D3444 with the lower jaw D3900, belonged to an older adult who had lost every tooth but one before death. The empty tooth sockets show extensive bone resorption, meaning the bone around them had been reabsorbed and remodelled. That takes time, so the teeth were lost years before this person died, not shortly before.

Living for years with almost no teeth raises a natural question: how did this person eat? In 2005 in Nature and in 2006 in the Anatomical Record, Lordkipanidze and colleagues suggested that others in the group may have supplied or prepared soft food. That idea is often repeated as early evidence of care.

Daniel DeGusta offered a caution. Toothless primates can sometimes survive by choosing naturally soft foods, so tooth loss on its own cannot demonstrate active care. The careful reading is this: Skull 4 shows a long survival with severe dental loss, which fits with help from the group but does not prove it. Either way, it is the skull of an elderly person who kept living a long time after the teeth were gone. Our story on what bones tell archaeologists covers how specialists read age and health from bone.

The Dmanisi human fossils are under the protection of the Georgian National Museum and the Dmanisi Reserve Museum. Skull 5, D4500 with D2600, has been displayed at the National Museum of Georgia in Tbilisi. The excavation area itself is preserved as the Dmanisi Archaeological Museum-Reserve, an open-air field museum built around the dig, which the Georgian National Museum describes as opened in 2009. Dmanisi is on Georgia's UNESCO Tentative List, the list of sites a country is preparing to nominate, rather than on the World Heritage List.

If you hope to see the skulls or the site, confirm the current display status with the Georgian National Museum, and opening hours and access with the Dmanisi Archaeological Museum-Reserve, before you go.

These questions come up often.