The Trilobites column over at the New York Times has a interesting story about the origin of chelicerates – spiders, scorpions, mites, horseshoe crabs, and others. Chelicerates are a diverse group of arthropods that consists of more than 120,000 known species. Member of this group are classified by having a pair of appendages called chelicerae. These appendages are adapted for various purposes like snatching prey, injecting venom, and even spinning silk.

Lloyd Gunther. an amateur collector, found the fossil that has been described as Megachelicerax cousteaui in the Wheeler Shale of Utah in the 1970’s. The specimen sat in a drawer at the University of Kansas Biodiversity Institute since it was donated in 1981. This research, published in the journal Nature, pushes the date of the earliest Chelicerate back to about 507 million years ago.

Before this research, the oldest clear fossil evidence of chelicerates dated back to the Early Ordovician Period around 485 million years ago. The complexity of these animals, some of which resembled horseshoe crabs, hinted that chelicerates originated during the earlier Cambrian Period. However, few Cambrian fossils presented compelling evidence of the group’s namesake pincers.

The newly described fossil was discovered by Lloyd Gunther, an amateur fossil collector, in the Wheeler Formation in western Utah, which dates back to the Middle Cambrian around 507 million years ago. At the time, the area was a warm sea home to trilobites and several soft-bodied critters that rarely fossilized.

Mr. Gunther donated one of these fossils to the University of Kansas Biodiversity Institute and Natural History Museum in 1981. The relatively unassuming fossil, which looks like the rusty imprint of a giant screw and measures less than 3.5 inches, sat for decades in the museum’s collection.