Fossils are time capsules embedded within almost every sedimentary rock. Most fossils are shells or isolated bones. The majority of fossils are shellfish that occupied neritic seas. When a shellfish dies it falls to the sea floor, where its soft body rots away. It’s hard,Aragonite shell becomes buried, and over millions of years the shell may be broken down, by water leaking through the sediments. Once the Aragonite is broken down it recrystallizes within the cavity, and creates a faultless replica of the shell. Fun Fact: Fossils of land animals are rare because they rotted away before being preserved. The Salt River, located in Maricopa County is blanketed with fossils. There are large paleo sites located around the state as well.   

Echinoderms are a group of marine organisms including sea stars, sea urchins, and sand dollars. They appeared about 540 million years ago, during the Cambrian period. 

Ammonites were squidlike shellfish that appeared during the Jurassic and Cretaceous Periods. These are one of the most abundant fossils on earth. They went extinct the same time as the dinosaurs, about 65 million years ago. 

Corals are ancient animals, with some specimens dating back to 500 million years ago. They are a skeleton made of Calcium Carbonate. Coral fossils exhibit numerous shapes, including spirals, disks, and brain-like domes. 

Plant Fossils are an ancient record of plants, appearing about 450 million years ago. Very specific conditions have to occur for a plant to become fossilized. The plant must be concealed within sediment quickly, to prevent it from decomposing. These fossils are used to better understand past climates. 

Bivalves are freshwater marine organisms with two shells united at a hinge. They were aquatic animals such as clams, oysters, mussels, and scallops. They date back to the Cambrian Period, and are found throughout all time periods. 

Brachiopods do appear similar to Bivalves, but they are unrelated animals. They do both share left and right shell symmetry however, Brachiopods are asymmetrical top to bottom. Brachiopods ruled the oceans around 540 to 252 million years ago.