A high-resolution x-ray scan of the newly described 305-million-year-old harvestman fossil (Hastocularis argus)

©Muséum national d'Histoire naturelle

Living harvestmen—a group of arachnids more commonly known as daddy longlegs—have a single pair of eyes that help them navigate habitats in every continent except Antarctica. But a newly described 305-million-year-old fossil found in eastern France shows that wasn’t always the case. New research published in the journal Current Biology and led by scientists at the American Museum of Natural History and the University of Manchester indicates that primitive harvestmen had two pairs of eyes, adding significant details to the evolutionary story of this diverse and highly successful group.