While cataloging hundreds of freshwater mussel shells collected at the end of the 19th century by the Dutch anatomist and geologist Eugene Dubois – the discoverer of Java man, the first known fossil of Homo erectus – on the banks of the Bengawan Solo river in East Java, Prof Roebroeks and his colleagues noticed that one of the specimens was engraved.
“It was a Eureka moment. I could see immediately that they were man-made engravings. There was no other explanation,” said team member Dr Stephen Munro from the Australian National University and the National Museum of Australia.
“It’s fantastic that this engraved shell has been discovered in a museum collection where it has been held for more than a hundred years,” said Prof Roebroeks, who is the senior author of the paper published in the journalNature.
Following the discovery, the scientists worked to establish the exact date of the shell, using two different methods to arrive at the final result of between 430,000 and 540,000 years old.
“This is the first time we have found evidence for Homo erectus (a hominin species ancestral to modern humans, dating from approximately 1.89 million years ago to 143,000 years ago) behaving this way. It rewrites human history,” Dr Munro said.
The Homo erectus engraving resembles the previously oldest-known engravings, which are associated with either anatomically modern Homo sapiens or Neanderthals from around 100,000 years ago.
“Until this discovery, it was assumed that comparable engravings were only made by Homo sapiens in Africa, starting about 100,000 years ago,” said Dr José Joordens of Leiden University, a team member and the lead author of the paper.
The early date and the location of the discovery on Java discount the possibility that the engraving could have been the work of Neanderthals or modern humans.
“It puts these large bivalve shells and the tools used to engrave them, into the hands of Homo erectus, and will change the way we think about this early human species,” Dr Munro said.
“The precision with which these early humans worked indicates great dexterity and detailed knowledge of mollusk anatomy,” said team member Dr Frank Wesselingh of the Naturalis Biodiversity Center in Leiden, the Netherlands.
It is unclear whether the pattern was intended as art or served some practical purpose.
“At the moment we have no clue about the meaning or purpose of this engraving,” Prof Roebroeks said.
The scientists also found that Homo erectus opened the shells by drilling a hole through the shell with a shark’s tooth, exactly at the point where the muscle is attached. Damaging muscles this way causes the valves of the shell to open, so that the contents can be eaten.
“It’s evidence that Homo erectus exploited these aquatic food resources, and fits with other evidence that they probably foraged in and around water,” Dr Munro said.
