Welcome to the Fossils Home Page




Casts & Molds


Molecular fossils



Drying & Dessication

Wax & Asphalt

Coprolites &Gastroliths

Trace fossils


Window to the past

Fossils pages in this web site introduce the common readers to types of fossils, conditions leading to fossilization, and the information contained in fossils. Last updated 8th Dec '96.Your feed back is welcome.

What is a fossil ?

There is a misconception that fossils are just a bunch of bones that make up an old dinosaur model, but there are many other aspects to be considered when defining a fossil. The most general definition of fossils refers to the remains of an ancient organism or the traces of activity of such an organism. There are two types of fossils- the body fossils and the trace fossils. Body fossils include preserved remains of an organism (i.e. freezing, drying, petrification, permineralization, bacteria and algea). Whereas trace fossils are the indirect signs of life that give evidence of the organism's presence (i.e. footprints, burrows, trails & other evidence of life processes).

Ages covered by fossils

Life began in the sea. The earliest evidence of life on earth is of marine animals, during the Precambrian era. But there is only sparse evidence of life before the Cambrian era. The oldest known Precambrian rocks, found in Africa and Australia, are believed to be more than three billion years old, and the fossils among them the oldest known organism on earth. The fossils found in rocks dating so far back are usually microfossils, such as elongated bacteria, Eobacterium and other water environment fossils. There have also been well defined remains of algae and bacteria found from nearly two billion years ago. Bacteria represents the first stage of recognizable organized life. The most common fossils are found in sedimentary rock. Sedimentation is the process of the accumulation of particles originating from the break up of pre-existing rock. Sedimentary layers act as evidence of the changing climate or movement of the continents during the passage of time. The Law of Superposition or Steno's law states that in a pile of undisturbed sedimentary rock, the oldest bed will lie at the bottom and the youngest on top. Layers of strata in different locations may have the same composition but carry fossils of a different time period, therefore a technique of zoning or an index fossil is used. The index fossils are specific animals or plants that had a broad geographical distribution but existed for relatively short periods of time. These fossils allow geologists to establish a parallel between layers using the presence of similar index fossils. Some excellent guide fossils are ammonites, whose evolution was such that each species lived for relatively short periods of time but had such a broad geographical distribution that they can be found today in stratigraphic rock layers often separated by great distances. The appearance of the same ammonite in different layers in different localities, gives evidence that those layers were deposited at the same time. Each time period is marked by an abundant radiation of many new life forms or the mass extinction of past life forms.

Types of fossils

Fossils undergo a variety of different fossilization processes, depending on the characteristics of the particular organism. There are various levels of fossil preservation, each containing its own clues pertaining to the organism. Fossilization at the cellular level varies in all organic compounds since not all cellular types are equally resistant to decay and decomposition. The same hold at the tissue level, where some tissue types are more susceptible to fossilization. The other two kinds include the organ level and organism level which provide information in the field of morphology and biology of the ancient organism. These levels are preserved by different processes that will be explored individually by this web site. Although there are an endless number of categories, we will focus on the broader mode of classification.

  • Permineralization: is the occurrence of decay of organic substances and filling of mineral material into every cavity of the organism, still retaining most information about the fossil.
  • Compressions: the two-dimensional compression which retains organic matter of the organism.
  • Impressions: the two-dimensional imprint most commonly found in silt or clay, without organic material present.
  • Casts & Molds: caused by deposits of sediment in cavities of organism, resulting in a three dimensional model.
  • Compactions: preservation of organic material with slight volume reduction.
  • Molecular fossils: deals with chemical data, preserving organic material, but providing no information concerning the structure of the organism.
  • Freezing: ideal fossils that are rare, everything up to internal organs are preserved in cold storage.
  • Amber: biological specimen that is encased in the hardened resin of a tree, in which the entire body may be preserved.
  • Drying & Dessication: fossils that have been thoroughly dried.
  • Wax & Asphalt: almost as good as freezing, but with the usage of natural paraffin.
  • Coprolites & Gastroliths: these categories deal with the indigestable remnants of meals.
  • Trace fossils: typically formed when an organism moves over the surface of soft sediment and leaves an impression of its movement behind.

How fossils are found ?

florissanstumps.gifThere are certain techniques that paleontologists might exercise to find fossils, but mostly finding a fossil has to do with chance and luck. However, all paleontologists need a place to start. No person would ever go on any kind of a hunt without having at least some clues about the general locations of the object that they are looking for. For paleontologists, this is where an extensive knowledge of the stromatolites, the different eras, the knowledge of which era(s) certain organisms dominated the earth, and which environment was most suitable for certain organisms. With these informations, the collector can eliminate certain localities depending on what kind of fossils they are searching for. For example, if a collector was interested in finding fossils of animals of ancient rocky shores, he/she would eliminate formations and beds in which remains are likely to be rare and poor. Paleontologists can also follow leads that other paleontologists or collectors have left behind in published reports. Soon every collector realizes that fossils of certain types are found in particular kinds of rocks. For example, marsh plants are most abundant in shales and sandstones between beds of coal, and coals are found in limy shales and massive limestones, many of which are the remains of ancient reefs. Using these techniques, process of elimination, and perhaps some luck, paleontologists have retrieved all sorts of fossils and animal remains from all sorts of geological areas.

Conditions that lead to fossilization

There are many conditions that contribute to the formation of fossils. However, the most common conditions include the possession of hard parts, a skeleton or shell, and a rapid burial after death. Besides being tough and hard, the organism must come to rest in a place where it stands a good chance of being buried before it decays or disintegrates. If the organism is not buried deeply and quickly, aerobic bacteria will reduce it to rubble; or water given enough time, will dissolve it. For this reason, fossils of some kinds of organisms are rarer than others. As for the skeletons, the skeletons that contain a high percentage of mineral matter are most readily preserved, and in contrast the soft tissue that is not intimately connected with skeletal parts is least likely to be preserved. Other conditions that lead to fossils include an environment that was biologically inert, areas that are receiving a large, steady supply of sediment, such as deltas of major rivers, and parts of the earth below sea level compared to those above the sea level. The ideal place to become a fossil is at the bottom of a quiet sea or lake where the prospective fossil is safe from damage and where it is covered rapidly with sediment. For this purpose, clay is an excellent option. The sediment protects the tissues and helps to exclude predators and solvent water.

What do fossils tell us?

The realm of which this question can be answered is very broad. The answers depend upon the fossils found in particular places, and upon the questioner. Nevertheless, there are certain general ideas that can be drawn from different fossils accordingly. Different fossils depending upon how they were preserved tells us different things. For example, fossils that are preserved in amber can tell us an extraordinary amount of information about the anatomy of that organism; since the organisms that are preserved in amber, mostly insects, are preserved as a whole usually without any disintegration of organs, muscles, and its coloring. Even bones devoid of flesh may tell a great deal about the soft anatomy. For instance, the area where the muscle attaches to the bone leaves marks that indicate sizes, shapes, and functions of these varied organs. Also, the cavities and the the channels in skulls give us an idea of their intelligence, behavior, and their principle features. Certain parts of certain fossils can also tell us about their growth, injury, disease, form, function, activities, and instincts. Fossils also record the successive evolutionary diversification of living things, the successive colonization of habitats, and the development of increasingly complex organic communities. Fossils also tell a great deal about their surroundings and the conditions under which they lived. Finally, fossils also contribute greatly to the study of evolution. They are the only direct record of what has in fact occurred in sequences of reproducing populations and in the course of the time on an evolutionary scale.


Amber || Casts & Molds || Compactions || Compressions || Coprolites & Gastroliths

Drying & Dessication || Freezing || Impressions || Molecular Fossils || Permineralization

Reference || Trace Fossils || Wax & Asphalt

Feed Back