Some 540,000 years ago, an ancient ancestor of modern humans took a shark tooth and carefully carved a geometric engraving on a mollusk shell.

The engraving -- the oldest piece of art ever found by at least 300,000 years -- as well as a shell tool were found at a site in what is now Java, Indonesia.

The work strongly suggests that Homo erectus, aka "Upright Man," was far more sophisticated than previously thought, being capable of cognition and behavior only attributed before to our species.

Photos: See the Ancient Engraving Up Close

The findings are published in the current issue of the journal Nature.

The age of the engraving is astounding, as no other art, even cave and rock paintings, are as old. The international team of researchers analyzed the imprint of the engraving to determine that Homo erectus made the engraving with a shark tooth.

"It was probably through the opening of shells with a shark tooth for food that at least one individual made a 'next step' by putting the tool to the shell for scratching lines, instead of, or in addition to, drilling a hole for opening the shell," lead author Josephine Joordens told Discovery News.

"With already a shell in one hand and a sharp tool in the other hand, it is not such a big step to take, but in our eyes now it was a giant leap for mankind, so to speak!" added Joordens, who is a post-doctoral researcher at Leiden University.

She and her colleagues made the determination after studying a fossil freshwater mussel shell assemblage from a site called Trinil in Java. The mussel shells originally were excavated by Eugène Dubois in the 1890s, but have been stored in the Dubois collection of the Naturalis museum in Leiden, The Netherlands. Sediment within the shells enabled them to be dated using both isotopic and luminescence methods.

The shell tool found within the assemblage was probably used as a knife for cutting or scraping, the researchers believe.

The prehistoric artist also put effort into the early engraving.

"When we tried to reproduce such a pattern by engraving a fresh shell with a shark tooth, we found it required a lot of strength and skill, especially to make such neat angles where the lines are exactly joined together," Joordens said. "The maker certainly must have put a lot of effort in it. Also, it is important to appreciate that originally the lines must have been white on a black-brown background: visually very striking."

Early Humans Brought to Life in Exhibit: Photos

The meaning of the design remains a mystery. The pattern could have held some symbolic significance, or the creator simply could have liked the linear design.

As for the shark teeth that the engraver used, only two sharks are known from the region at the time: the Ganges shark and the sand tiger shark. It's possible that Homo erectus hunted sharks for their meat, but the early humans might have also just found the teeth, as sharks tend to shed them a lot. The teeth could have washed up on a river shore, or on a nearby sea coast.

Life for Homo erectus at Java appears not to have been too miserable.

"The good thing about these aquatic resources (shellfish) is that they are abundantly present and easy to collect, and very nutritious, so this would imply that life was not too tough for Homo erectus there," Joordens explained.

Stephen Munro, a curator at the National Museum of Australia and a researcher at Australian National University, told Discovery News that the archaeological finds, as well as the stocky build of Homo erectus, suggest that the population was specialized for foraging in relatively shallow waters for slow-moving foods, such as shellfish.

"They no doubt spent much of their time on land gathering food, and we know they butchered large mammals, but their very heavy bones suggest they never moved far from water, and apparently regularly foraged in the water," he said.

The possibilities concerning what happened to Homo erectus later are profound.

"It may have evolved into Homo sapiens and perhaps into multiple species," Joordens said. "All modern humans today may be distantly related to Homo erectus."

Another possibility is that people of Asian and European ancestry "may have, in addition to Neanderthal and Denisovan genes, also some Homo erectus in our genomes," she said.

Joordens and her colleagues are already planning a follow-up study on Homo erectus, to determine what other "modern" behaviors it was capable of performing.