It's possible that a clam shell scratched by Homo erectus — an early hominid — might be our oldest-ever example of artistic work. Or just a thoughtless doodle.

The shell, which was found in Indonesia in the 1890s, is described in a paper published Wednesday in Nature. While studying these shells, some of which featured marks from tool use, Leiden University biologist Josephine Joordens  and her colleagues noticed a faint zigzag pattern on one of them — only visible from a certain angle.

But although the markings are faint, the researchers believe they were put in the shell intentionally.

The carvings, they report, resemble geometric engravings made intentionally in South Africa some 400,000 years later. They believe that their "artist" worked carefully and deliberately at the shell, in contrast to those that had clearly been worked at to get to the food inside.

"We've looked at all possibilities, but in the end we are really certain that this must have been made by an agent who did a very deliberate action with a very sharp implement,” Joordans told Nature magazine. When her team worked to replicate the action, they found it extremely difficult to create the long, uninterrupted grooves, which would have appeared as striking white against the background of the shell's brown coating.

Given the age of the shell and its location, the etcher must have been Homo erectus. That would be pretty surprising, since scientists didn't think that abstract art emerged before our own species' evolution until very recently. A few months ago, researchers reported evidence of an engraved pattern made by Neanderthals — but Homo erectus came even earlier.

It seems likely that the markings were deliberate, but whether or not we should count them as "art" is another debate entirely. It's possible that the markings were absent-minded doodling, without any artistic intention behind them. Unfortunately, we don't have any way of guessing the intention of the individual who made these squiggles, so the question of whether these early hominids were capable of abstract thought remains unanswered.