Fossils Discovery Kit


American Mastodon, partial skeleton. This mastodon in the GRPM's Collection, nicknamed Smitty, was found in October of 1985 in Grandville, Michigan. A detailed study of the skeleton determined Smitty was male and around 33 years when he died. Smitty’s skeletal material has been radiocarbon dated back to ~10,920-12,160 years ago. View the complete record on the GRPM Digital Collections at

What are fossils and how are they created? 

Fossils are the remains or physical evidence of once living animals and plants. The entire organism or only a small part of the organism can be preserved as a fossil.  Fossil remains can also be skin or body impressions of an organism or a trace left by an organism while performing some activity, like walking, running, burrowing, or feeding.  

When an organism dies, its remains usually decay and rot away. However, sometimes, plants or animals die and the remains get buried quickly enough under sediment that it turns into a fossil. The hardest parts of an organism are usually preserved as a fossil, such as bones, teeth, shells, or the exoskeletons of insects or crabs.  This is because they are the most heavily mineralized, making them resistant to weathering and destruction.  Think about how strong bones and teeth are compared to the soft, fleshy parts of a body, such as skin, muscles, or organs.  If the conditions are just right, the soft parts of an organism can be preserved in the fossil record, but this is very rare. Hair, feathers, fingernails, and claws are not commonly found in the fossil record, because they are composed of a material called keratin, which isn’t as strong as bone, teeth, or shell. 

Fossilization is a very rare process; in fact, over 90% of all living things never become a fossil. The process of an organism becoming fossilized typically happens very, very, slowly and will take 10,000s to 100,000s of years. Fossilization can happen in a variety of ways, but the two most common processes are described below: 

  1. First, the soft tissues of dead organisms decay, leaving just the harder parts such as bones and teeth. If these body parts become buried quickly enough, the sediment around them can begin to thicken and turn to stone. Eventually, the skeleton dissolves, and a mold forms in the stone where the skeleton was. This way, the shape of the original skeleton is preserved in the rock. Rocks that are found with these impressions are called mold fossils. 
  2. Cast fossils actually go a step farther. They can be formed if sediment or minerals fill the molded impression. The minerals or sediment deposited in the mold form a hard cast with the same size and shape of the original skeleton.
The man-made cast of the turtle Allaeochelys crassesculpta includes the skull and shell of the turtle.

What can we learn from fossils?

Fossils are the ancestors of today’s living organisms. Through fossils, we can learn about plants and animals that have gone extinct and no longer exist on Earth. Fossils are our only evidence about what these organisms looked like. With a fossil record, we can find out information such as: 

  • Details of an organism’s anatomy, shape and size
  • Where these prehistoric plants and animals lived
  • Information about an organism’s life, including details of growth, injury, disease
  • Clues to the habits or behaviors of an organism. Trace fossils, such as tracks, burrows or bite marks can help us understand how organisms moved, what they ate or where they made their home.
  • How long ago an organism existed on Earth (based on which rock layer the fossil is found in)
  • How life has evolved or progressed through time

Check out this video from the Grand Rapids Public Museum's science curator, Dr. Cory Redman. He explains what can be learned from a very special specimen in the Collection:

This is a 3D rendering of a cervical vertebra of the American Mastodon, "Smitty"