WHAT IS A FOSSIL?

Fossils are often the only clues to animals and plants that lived millions of years ago.  But how were they made?

Fossils, derived from the Latin and means ‘what can be dug up’, are the remains or prints of animals and plants that have been preserved in rocks.  Quite often, only the hard parts of an animal, such as the teeth or bones, are left.  The rest has rotted away.  But even when nothing remains of an animal, it may have left a hollow, the exact shape of its body, in the rock.  Sometimes an animal left a footprint when it walked in soft sand or mud.  A single footprint may be all that remains of an animal that was as big as four cars.  Fossils can take millions of years to form.

The scientists who do all the detective work on fossils are called paleontologists.  They have found fossils all over the world.  Their job can be very difficult because the fossil bones are often scattered in pieces.  Only very rarely is a whole skeleton preserved in the rocks.  Paleontologists identify the fossil bones, remove them from the ground, put them together, like a jigsaw, and decide how old they are.  You can see the results of their work in natural museums where dinosaur fossils are mounted and put on display.

1.                  When a dinosaur died, its body may have fallen, or been washed, into a river.

2.                  The dead body lay on the bottom of the river and the flesh rotted away.

3.                 The skeleton was gradually buried under mud, and minerals from the water seeped into the bones and preserved them.  Over millions of years, the mud turned into layers of rock and the dinosaur skeleton became a fossil.

4.                 Millions of years later, the sea level dropped.  The wind and rain wear away the rock revealing the fossil:  proof that dinosaurs once lived.

Fossil bones and teeth are not the only clues that these giants of the past left behind them.  Dinosaur footprints and the imprint of scaly skin, made in soft mud millions of years ago have been found.  Some of the most remarkable fossils found are dinosaur droppings.

How Fossils are Preserved Specific conditions must be present for the remains or signs of an organism to fossilize.  Most dinosaur fossils found in western North America were preserved in sediments associated with water.  High rates of sedimentation in rivers and streams would quickly cover an animal's bones and protect them from currents, scavengers and other things that scatter and break down bones.   Fossilization occurs when ground water minerals slowly fill tiny spaces in the animal's bones, or replace the specimen's original minerals.  Or, an organism or object encased in rock may completely dissolve, leaving only an imprint of the original shape.  These natural molds can fill with ground water minerals, becoming natural casts.   If initial burial happens quickly after an animal dies, impressions or molds of the animal's skin may be preserved.  Fossilized footprints are molds of an animal's feet.  Fossil footprints can fill with sediment and minerals which can become casts of the prints.