Fossilized horseshoe crab, 15 centimeters long, with its trackway preserved in lithographic limestone Mesolimulus walchi Found in Solnhofen Formation, an ancient saltwater lagoon of Upper Jurassic Period, 161 to 145 million years ago Solnhofen, Ge

Fossilized horseshoe crab, 15 centimeters long, with its trackway preserved in lithographic limestone, Mesolimulus walchi, Found in Solnhofen Formation, an ancient saltwater lagoon of Upper Jurassic Period, 161 to 145 million years ago, Solnhofen, Germany, (Specimen courtesy of Raimund Albersdoerfer, Germany), (Photo by Wild Horizons/Universal Images Group via Getty Images)