By Will Dunham
WASHINGTON (Reuters) - It's a simple zigzag design scratched onto the surface of a freshwater mussel shell on the Indonesian island of Java about half a million years ago.
But scientists are calling it a milestone achievement for early humans and an indication that the species Homo erectus, which preceded our own species Homo sapiens, possessed more advanced cognitive abilities than previously thought.
In a study published on Wednesday in the journal Nature, the scientists describe a collection of shells from the Trinil site in Java, a treasure trove of Homo erectus skeletal remains and artifacts.
One shell was fashioned into a tool with a smooth and polished edge, probably used as a knife or scraper. Another has the zigzag pattern, most likely produced by scratching the shell's surface with a shark's tooth, that the scientists say represents the earliest geometric engraving known to exist.
Prior to this, the oldest similar artifacts were about 110,000 and 100,000 years old, found at sites in South Africa and made by Homo sapiens long after Homo erectus had disappeared, said biologist Josephine Joordens of Leiden University in the Netherlands.
"This changes our view of the degree of cultural complexity characteristic of this fossil species and indicates that stone tools are a pale and incomplete reflection of the total complexity of techniques used at the time," Joordens said.
The researchers determined the age of the Trinil shell artifacts to be between about 400,000 and 500,000 years old.
Leiden University archaeologist Wil Roebroeks said the meaning and function of the zigzag design remain unknown.
"Most of it consists of a zigzag made in just one session by a pointed tool, certainly by the same person. The pattern was engraved carefully, putting a great deal of attention in making clean angles and straight lines of similar length," added archaeologist Francesco d'Errico of France's University of Bordeaux.
The use of the shells as a source of food, raw material for tools and a medium for engraving "suggests a previously unsuspected cognitive plasticity," d'Errico added.
Homo erectus, meaning "upright man," is thought to have lived from about 1.89 million to perhaps 143,000 years ago and was the first early human species with limb and torso proportions resembling Homo sapiens. Homo erectus was omnivorous, used stone tools and fire but possessed a much smaller brain than modern humans.
The first Homo erectus fossils ever discovered came from the Trinil site in 1891.
(Reporting by Will Dunham; Editing by Sandra Maler)