The ancient relatives of modern-day humans not only ate freshwater shellfish, but engraved their shells and used them as tools, a new study finds. Researchers in Java, Indonesia, discovered engravings on a shell that dates to between 540,000 and 430,000 years ago. The ancient artworkcould be the oldest known geometric carving made by a human ancestor, the researchers said. It could indicate that Homo erectus, the ancestor of modern humans, may have been smarter than was previously thought.