Fossils are the remains of plants and animals that lived long ago. Most
fossils were formed when the hard parts of an animal were buried in soft
mud, silt, or sand. Over thousands of years the original bone, wood, or
shell decayed or dissolved away, but its shape was preserved by minerals
that seeped in and replaced the original material. Sometimes a fossil
organism can be preserved exactly as it was when it died. This is very
There are two main types of fossil preservation,
without and with alterations. Most common is fossil
preservation with alteration. This is when the original organic material is
partially to fully changed into new material. Types of preservation with
alteration include carbonization, permineralization, recrystallization, and
The second type of fossil creation is direct
preservation of fossils without alteration. The most common directly
preserved fossils are unaltered hard parts of a living organism, like
shells, teeth, and bone. This material is unchanged, except for the removal
of less stable organic matter. Examples of this type of preservation include
fossil corals, shells, sponges, microscopic fossils and a host of other
organisms with hard parts. In rare circumstances, preservation of the soft
parts of an organism may occur. An example is Dimo, a baby mammoth found in
the tundra of Siberia. The ice "froze" all the body parts. The
preservation was so good that paleontologists were able to determine that
the baby mammoth died of blood poisoning. Another example is an insect which
has become "stuck" in tree resin. When the resin fossilizes to
form amber it preserves the insect. This was the whole premise for the book
and movie called "Jurassic Park."
Show the students a fossil and its present day equivalent.
compare degree of preservation, color, texture, and any other
characteristics that they see.
Emphasize that fossils do not represent the entire animal, so
paleontologists (scientists who study fossils) must to be very careful
when making conclusions about the original living organism.
Discuss with your students that there are many types of fossils,
representing many kinds of organisms. Not all fossils that we find
represent extinct organisms. Dinosaurs are extinct, but sharks and clams
are not. The living representatives of sharks and clams still look
similar to the fossils that their ancestors left behind. Lead the
students into a discussion concerning the following fossils, and talk
about whether the specimens represent extinct animals (referring to the
organism as a group, not as an individual species) and what part of each
organism might or might not be preserved in the form of a fossil. Use
the following diagram to guide you.