A fossil is a complete or partial imprint of the remains of a plant or animal in a rock formation, or a crude snapshot of how life was millions of years ago. The unique representation of ancient history that fossils provide has made selecting a state fossil a common practice for many state governments in the United States. A fossil is typically selected to be a state symbol because it is prevalent in that state. The state fossil, however, may also be selected to show how animals have changed since ancient times, what unique animals lived in the state in prehistoric times, or what the habitat was like when the fossilized animal was alive. Not all of the states within the United States have selected an official state fossil.
An example of a state fossil selected to show how a modern day animal has evolved is the state fossil of Minnesota, the Castoroides ohioensis, commonly known as the giant beaver. These prehistoric animals looked much like the modern beaver but were about 8 feet (2.4 m) long and weighted about 440 pounds (200 kg). This would make this archaic beaver the size of a modern day bear.
The sabre-toothed cat is an example of an official state fossil selected for its uniqueness and popularity by one of the Western states — California. This animal looked much like a female lion, but had a set of canine teeth that protruded from the upper jaw in a sabre-like taper that gave this animal its common name. The sabre-teeth were usually 7 inches (about 18 cm) long. These animals have long been a popular symbol of the ice age along with the woolly mammoth, which probably accounts for the state of California selecting this fossil as a state emblem.
The terrain of the United States is nothing like it was 400 million years ago or even 40 million years ago. For example, more than 400 million years ago, New York State was covered by a sea and was the home of the Eurypterus remipes, or sea scorpion, which is most similar in anatomy to the contemporary king crab. The sea scorpion was selected as the state fossil to show that New York was once a briny sea. This rare eurypterid was also selected because it and many of its relatives were fossilized in a large band of rocks extending about 70 miles (113 km) across New York State. This fossil-concentrated band of rocks has become famous among paleontologists worldwide.