Scientists made 3-D models of two ancient harvestmen species, members of groups called the Eupnoi and Dyspnoi, using fossils discovered in mineral deposits in France more than 20 years ago. (Related picture: "Ancient Spider 'Digitally Dissected.'")

The fossils were "preserved in nodules of iron carbonate, or siderite," study team member Russell Garwood, a paleobiologist at the Natural History Museum in London, said via email.

This mineral "precipitates out early in the history of the rock, sometimes around animal remains, and prevents [the remains] from being crushed. ... The animal then rots away, leaving a void in its shape."

The new re-creations support the idea that daddy longlegs have changed remarkably little over time, even though the ancient arachnids lived at a