Mastodon excavation in Angola, Louisiana. Cast Fossil Fish Imprint Trace Fossils: Dinosaur Tracks HYRACODON Sabertooth Cat Sabertooth Cat with Tar Pit Finish Termite and Tree Leaf in Amber Spider and Feather in amber. Precambrian Era Mawsonites, similar to jellyfish, Australia Smithsonian Institution, Museum of Natural History Unnamed "spindle-shaped organism" from Newfoundland Smithsonian Institution, Museum of Natural History Trilobites thrived worldwide from the Cambrian period (600 m.y.a.) through the Permian (230 m.y.a.). Paleozoic Era Ammonites are spiral-shaped marine cephalopods that lived through the Paleozoic and Mesozoic eras ( m.y.a.) and became extinct with the dinosaurs. Mesozoic Era Armored dinosaur Stegosaurus, a plant-eater of the late Jurassic Period, about 135 million years ago.Stegosaurus, Cenozoic Era The Age of the Mammals