A new fossil reveals that the ancient ancestors of today's spiders had four eyes.

A fossil of an ancient, "daddy Longlegs"-like arachnid, which is the ancestor of today's harvestmen spiders, was recently found in eastern France, according to LiveScience.

The discovery may shed light on the evolution of the arachnids, which can be found on every continent except Antarctica.

Scientists used X-ray techniques to make images of the 305-million-year-old harvestman fossil. Their study reveals that the two sets of eyes found on the harvestman species, which is called Hastocularis argus, were separated. They had one pair close to the center of the head, and another on the sides of their head.

The ancient arachnids were the precursors to the spider, but were not exactly spiders themselves.

"Although they have eight legs, harvestmen are not spiders. They are more closely related to another arachnid, the scorpion," study author Russell Garwood, a paleontologist at the University of Manchester in the United Kingdom, said in a statement.

Today's arachnids, which include harvestmen as well as spiders and scorpions, can also have two sets of eyes. However, modern harvestmen only have one set that are located close to the center of the body.

"These findings represent a significant leap in our understanding of the evolution of this group," Garwood said.

The scientists tracked their "lost" set of eyes by examining the genes of current-day harvestmen embryos, and they found that the spiders still have the gene for the ancient additional eye set.

Harvestmen skeletons that belong to the same group of terrestrial arthropods tend not to preserve well, which makes it difficult to find their fossils.

"As a result, some fundamental questions in the evolutionary history of these organisms remain unsolved," said Prashant Sharma, a postdoctoral researcher at the American Museum of Natural History in New York City.

The researchers' findings were published Thursday in the journal Current Biology.