Image courtesy Garwood et al, Nature Communications

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Three-dimensional model of a harvestman of the Eupnoi group.

Image courtesy Garwood et al, Nature Communications

Early Daddy Longlegs Revealed in 3-D—Bugs Evolved Little

The spider cousins have barely changed in 305 million years, fossil study says.

The spiderlike creatures known as daddy longlegs looked just as creepy 305 million years ago as they do now, according to new computer models that show the bugs settled into their modern forms early.

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 time when their spider and scorpion relatives were still evolving into their current shapes.

For example, spiders living 300 million years ago still had hints of segments on their back halves, a trait modern spiders do not have, Garwood said.

Scorpions living back then were also still relatively primitive, said Garwood, who conducted his research while at the U.K.'s Imperial College London.

Unlike modern species, ancient scorpions "had compound lateral eyes, median eyes near the front rather than the middle of their carapace, and a different position of the opening into the lungs," he said.

Fossil Daddy Longlegs Were Forest Bugs

The new 3-D models reveal that the two ancient harvestmen species were both likely forest dwellers.

The model of the Eupnoi species, for example, revealed long legs that were curved at their ends, a feature some modern harvestmen species use to grip onto vegetation while moving from leaf to leaf.

By contrast, the Dyspnoi fossil had spikes on its back that it may have used to discourage the attention of predators.

A modern species of harvestman with similar spikes lives in moist, woody debris on the forest floor, and the team thinks the ancient Dyspnoi led a similar lifestyle.

The fact that there were two distinct lineages of harvestmen living 305 million years ago supports the theory that the creatures were among the earliest arachnids to take a major evolutionary turn, the team noted.

"These studies show that harvestmen were among the earliest arachnid groups to split off from this arachnid lineage to become their own group," Garwood said.

The fossil-harvestmen research is detailed in this week's issue of the journal Nature Communications.