|Themes > Science > Paleontology / Paleozoology > Fossils And Fossilisation > General Discussion of Fossils > Definition of a Fossil|
The purpose of this document is to familiarize you with some of the major groups of fossils which have proved important in determining relative time (in allowing us to establish a sequence of events for the history of the Earth).
Commonly, paleontology is divided into three areas:
2) invertebrate paleontology concerns itself with animals without backbones, and
3) paleobotany, the study of fossil plants.
Vertebrate paleontology is significant because it provides information on the evolution, distribution and habits of the group of organisms to which we belong; and because vertebrates have been the most successful large* animals to adapt to land.
Despite occasionally spectacular finds, the fossil record of plants is not
as well known as that of animals, and in general, plant fossils have not
yet turned out to be as useful geological tools as animal fossils.
Palynology, the study of plant pollen has been extremely useful in the
study of past ecosystems.
There are many different ways in which an
organism can leave evidence of its presence.
||Two examples of
Both are from the
Green River shale.
|Not all evidence includes the actual remains. Indirect evidence includes molds, casts, imprints, coprolites and tracks. Molds are the hollows left in the surrounding material (the matrix) after the remains of the organism have been dissolved or removed. Some of the most famous historical molds were discovered in Pompei where the remains of fleeing Romans were entombed in the vulcanic ash of the 79AD eruption of Mt. Vesuvius. Archeologists were able to fill these molds with plaster and these casts provide us with a glimpse of the people as they fell and died from suffocation. This process occurs when a different mineral fills in molds and preserves a replica of the original. Leaves and other fossils often leave their imprints on rocks and, in a way, tracks are nothing but a special kind of imprint. In some cases we only know that an organism existed because we have found its tracks. Finally coprolites, (fossilized feces) have given us much information about the digestive systems and dietary habits of many an extinct animal, as well as for early man.|