The tail spike belonged to a dinosaur that lived in the Upper Jurassic period, 150 million years ago. Depending on the species, the animal reached a length of 7-9 meters. It was a quadrupedal herbivore with a heavy body and two rows of vertical plates on its back. It carried 2 pairs of spikes on its tail. It used them as a defence against predators. The fossil was found in the Morrison Formation of the Cleveland-Lloyd Quarry in Utah. Not only Stegosaurus bones but also large predatory dinosaurs and the remains of long-necked sauropods have been found in the sedimentary rocks of this formation.