Paleontology• Natural History Museum definition:

(www.amnh.org/ology/)

What is a Fossil Anyway?What is a fossil? Simply put, a fossil is the remains or evidence of any creature or plant that once lived on the Earth.

There are quite a few fossil classification systems in use today, but my favorite is the one used by Peter Larson and Kristin Donnan in their book, Bones Rock! They group them into two categories:

Type I-the remains of the dead animal or plant or the imprint left from the remains. • Type I includes:• bones • teeth • skin impressions • hair • the hardened shell of an ancient

invertebrate (an animal without a backbone) like a trilobite or an ammonite, or the

• impression of an animal or plant, even if the actual parts are missing.

Amber

Largest Fossil Spider Found in Volcanic Ash (Igneous Rock)

Fossil Clam Shell with Calcite (mineral)

Pteriodsperm Found in Coal Mine in Illinois (extinct fernlike plant)

Skeletons of Basilosaurus, a whale ancestor, reveal the leviathan still retained tiny hind legs. Smithsonian….discovered in Wadi, Egypt

Whales evolved from mammals that adapted to hunt in oceans.

Order Clupeifomes; Family: Clupeidae;

Genus and Species: Knightia eocaena

Age: Eocene (can be found in Green River Basin, Wyoming)

Type II- Something that was made by the animal while it was living that has hardened into stone. These are called trace fossils.

• Type II includes:• footprints • burrows or worm holes• coprolite or animal poo

Type I• Type I fossils can be the actual

thing that it once was, like a piece of bone or hair or feather. More often the bone material is replaced by different minerals contained in the liquid of the sediments that buried it. What was once bone is now some sort of crystal.

Permineralization• This process also takes place with shells, exoskeletons and wood. If the spaces in the bone are filled with liquid minerals which later harden it is called permineralization.

Petrification• Sometimes the organic material is

dissolved by the mineral-laden water. The process happens so slowly that each cell is dissolved and replaced by a particular liquid mineral before it hardens. This is called petrification. In petrification, every detail down to the cellular level is duplicated in the minerals.

Type I• Type I can also be molds or casts

of the original animal or plant part. If the original organism decays, leaving an imprint and an empty space, it is called an exterior mold or simply a mold. If a space in the structure is filled with minerals and then the original animal or plant part dissolves, it is called a cast.

• http://www.fossils-facts-and-finds.com/geology_activities.html

How Fossils are Formed

Sedimentary Rock• Most (not all) fossils are found in sedimentary

rock. • This type of rock is formed when existing rock

broken down by wind, water, or ice. • The small particles are carried into lakes or

seas where they settle in the bottom.• Over time, the layers build up. • Organisms that die become buried in the

sediment as well. • The weight of the layers causes the lower

layers to turn into rock.• If conditions are right, organisms are

preserved within the rock.

RelativeDating – Newer speciesare found on thetop layers.

Older species are found on bottom layers.

Relative Dating • Compares the ages of different fossils to determine if a fossil is older than another by the rock layer in which it is found.• Although useful it does not tell the actual age of a fossil.

Radioactive DatingRadioactive dating or carbon dating – scientist use radioactive elements to determine the actual age of the fossil. While alive all living things take in small amounts of radioactive elements. When they die, they stop taking in radioactive elements. The time it takes for half of those radioactive elements to decay is calledhalf-life. Scientist use this half-life to calculate the age of the fossil.

SlothFernbank MuseumAtlanta, GA

Frilled Sharkrare “living fossil” - Japan