About Fossils

For additional information about fossils, follow these links:

Fossil Wood, Bone and Shells
Fossil Amber
Annotated Geological Time Scale

The study of fossils, and fossil life, is called paleontology. Fortunately, we don’t have to be paleontologists to appreciate fossils! Many scientists do devote their life studies to fossils, and for some very good reasons:

  • To learn about the similarities and differences between ancient and modern life forms. It’s fun to look at reconstructions of ancient critters and plants that are weird by modern standards (ranging from T Rex and Megalodon to ginormous trilobites). “Phylogeny recapitulates ontogeny” so we can also gain insights into the complex functions of modern organisms (including humans) by studying ancient ones.
  • To learn about the similarities and difference between the ancient and modern environments in which animals and plants live/d – paleontology helps us know earth history, including plate movements, as well as climate change.
  • To learn about ancient events that caused widespread extinction of species (volcanic eruptions, meteorite impacts, earthquakes, floods, etc.)
  • To learn how ancient organisms responded to drastic changes in their environments

Fossils are what remain in the geologic record of ancient life, in the form of body fossils and trace fossils.


Below: left, fossil trilobite; right, fossil stegosaurus skeleton; all from the Smithsonian Institution collection.

trilobite from Smithsonian Institution collection

How do dead plants and animals get turned into fossils?

Most don’t. Organic material decays after death, and/or is eaten by other life. The preservation potential (to become a fossil) of a dead organism is quite low for all terrestrial species. Vultures and raptors eat dead critters, and you know what happens to the lettuce you forgot in the refrigerator and put in the compost pile. Rapid burial by sediment in an oxygen-poor environment is required for most fossil formation. Tar pits, swamps, glacial fields, some deserts and the deep ocean are some places where this can happen.

After 100,000 years or more of being buried, little is left of the original plant or animal.* Body fossils are molds or casts of the original critter, most often hard parts like shells or bones. For some body fossils the original bone or shell has been replaced by another material (calcite, chalcedony, or pyrite). In rare examples an entire body is preserved, such as a woolly mammoth in ice, or a whole spider in amber.


Trace fossils record the presence of the fossil organism, not the organism itself – burrows, footprints, and fossil poop (coprolites) are all examples of trace fossils.

Below: left, fossil fish Knightia (Wyoming); right, fossil dinosaur poop (coprolites)

fossil fish knightia image from Smithsonian Institutionfossil poop coprolite dinosaur image from Smithsonian Institution

*Recent developments in the isolation and extraction of genetic material such as DNA and RNA from petrified or trace remains has led to many exciting new discoveries in the field of paleontology.

Fun Fossil Websites

The US National Park service website has a lot of information about fossils, including:

Most states have an official state fossil; find your state's fossil HERE. The official fossil of New Mexico is Coelophysis bauri, a theropod dinosaur. 

Best places in the US to see fossils