It looks similar to human fossils before, but the anatomy of a brain shell is similar to that of a human species that is newer to us.
The features of this skull are similar to those of early humans and today's humans. (Georgian National Museum / National Geographic)
A new skull discovery, estimated to be over 1.8 million years old, has reinvested the debate over the identity of the ancestors of humans. Uncovered in the Caucasus, Georgia, they call this discovery the "Skull 5" consisting of the most complete jaw and skull that became the turning point of early human history.
Initially the researchers led by an anthropologist from the National Museum of Georgia, David Lordkipanidze, had discovered the complete lower jaw of human fossils in 2000. Five years later the complete skull appeared on the fossil-rich site at Dmanisi site, 96 miles southwest of Tbilisi.
Skull 5 is often called paleoanthropologists as a mosaic or a mixture of features seen in earlier and subsequent humans. The facial skull, large teeth, and small brain size resemble the earlier human fossils, but the detailed anatomy of the braincase resembles that of the more recent human species we call Homo erectus.
The combination of features has sparked prolonged discussion about whether Dmanisi man is an early form of Homo erectus which is a different species called Homo georgicus or something else.
The newly discovered skull is not the only skull found in Dmanisi. At least five relatively complete skulls have been recovered there in the last two decades. These individuals may not actually live with each other, but seem to occupy the same place in a few thousand years more than 1.75 million years ago.
Using morphometrics to measure the shape of the skull on each fossil skull, Lordkipanidze and colleagues found that Dmanisi humans vary from one another in facial features and brain size. Despite their slight differences, they are all the same species.
Anthropologist Fred Spoor, from the German Max Planck Institute for Evolutionary Anthropology, agrees that Skull 5 is a truly amazing specimen. "The skull will help researchers find out what really happened at the beginning of the evolution of Homo erectus," said Spoor.
The discovery of one species provides widespread implications for the history of humanity. Scholars see the Dmanisi population as a different variation of the Homo erectus man or perhaps as a new species. It may be the early emigrants from Africa and other parts of the early branches of the human family tree.
In the new study, Lordkipanidze and co-authors point out that the population of Dmanisi was actually part of a single human lineage containing some early human species that are considered to be different from Homo erectus. "Dmanisi is an interesting combination of primitive faces, primitive teeth, primitive brain sizes, but if I'm going to take a chainsaw and cut my face and show a braincase to a colleague, I'm pretty sure that people will say it's Homo erectus," Spoor said.
Lordkipanidze and colleagues placed them in an ancient human ancestry that might stretch back as far back as 2.4 million years ago in East Africa, when the first human species, Homo habilis, emerged.
"Dnanisi, the division between Homo habilis and Homo erectus in the early days.Dnanisi is a snapshot in time, like a time capsule," Lordkipanidze said.
He suggests that the research team has not finished working, and early human fossils may still be found. "We can say with certainty that Dmanisi has great potential to produce new discoveries,"