Mesolimulus walchi   CLASS - Merostomata ORDER - Xiphosurida FAMILY - Mesolimulidae GENUS/SPECIES - Mesolimulus walchi ROCK UNIT - Solenhofen Limestone AGE - Upper Jurassic (150 million years old) LOCALITY - Eichstatt, Bavaria, Germany Horseshoe crabs date back to the Silurian Period (more than 400 million years ago). Fossils of the late Paleozoic horseshoe crab Euproops show that this group of animals has changed very little in the last 300 million years. This specimen preserves the rarely seen legs of the fossil horseshoe crab. Horseshoe crabs are very rare in the fossil record, because their thin, poorly mineralized exoskeletons (outer "shell") did not survive in most sedimentary environments. The Solenhofen Limestone is unusual because it preserved many types of soft body parts and weakly mineralized skeletons, such as the feather impressions of the oldest known bird, Archaeopteryx. PRI 41773