Aug 02 2013

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Classification of Fossils

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We used specific scientific words to describe morphological features and other of organisms. Both the fossils and trace fossils can be analyzed in several different criteria. Special thanks goes to Kathleen Nester from the University of Calgary for helping me understand the morphological concepts.

Physical Characteristics

When Geologists, Paleontologists and fossil hunters search for fossils, they are heavily depend on the key identifiable physical characteristics of organisms. There is no such thing as a clear line between the difference between what is a fossil and what is not. Almost anything that is buried under the Earth can be considered as a fossil. However, the importance of the specimen to the Geologic time is very important. Let’s look at the physical descriptors.

After we established a sample is a true fossil, the next step is to determine its identity. There are several different methodologies in separating samples into Hierarchy of Life (K-P-C-O-G-S). Separation by physical characteristic is known as morphological division (or morphology).

Symmetry and Geometry (Gastropods, Ammonites and Brachiopods)

Symmetry and the shape (geometry) of fossils are determined by the organism’s DNA and the environment.

The best example of a complex natural symmetry is the starfish in the Class Asteroidea. It has a unique pentameral symmetry, which is not commonly found in other Groups, Classes or Genus. Therefore we can use this as an identifier for this type of fossil. There are other types such as radial symmetry, spherical symmetry and longitudinal symmetry to differentiate the variates of organisms into Classes and Genus.


Phylum Brachiopoda

Strophic shells have a true hinge line and may also have inter-areas; non-strophic shells have no true hinge line but may have palintropes(1). This is an external hinge structure. A strophic hinge line is straight while a non-strophic hinge line is curved(2).

Concavity is of a specimen can be obtained using external and or internal surface features. There are few descriptors we use; biconvex, convexo-concave, and concavo-convex based on the physical shape of the brachiopod shells. It is recommended to name the brachial valve first before naming the pedical valve. The pedical valve contains foramen(2).

Shell features such as also used for differentiation. Plicate literally means “folded” contains corrugations that go through the entire shell. Rugate are thickening of the shell in intervals, which radiates outwards in “circular” formation. Costate are also thickening intervals of the shell radiating directly opposite in “lines” formation(2).

Associated Time Frame

Geological Time Scale is somewhat subject to interpretation. There are several observations can be obtained in order to prove or disprove the boundaries of Epochs, Periods, Eras and Eons. If you “Google it”, you will come across several different versions of the Time Scale. A Geologic Time Scale with fossils superimposed can be found here. Please keep in mind that Science is always changing and the Geologic Time Scale has be adjusted almost in yearly basis as new evidence surface through research.

Not all organisms remains

Just because a time scale has a boundary at a certain age, it does not mean that the fossils appeared must also ceased to exist. In fact, there are more fossils that cut across divisions in the time scale than there are once bounded by them. The fossils or trace fossils that only appear within a certain division is usually known as an index fossil, because they can be used to identify (hence “index”) the time frame.

Association to Each Other

Based on where the fossils are found and the fossils around the one we interested in we can expand our understanding. For example, if a large fossil is surrounded by a relatively small fragmented bones type fossils, this may be an indication the large one is the predator and the small bones are from a prey.

Size doesn’t matter?

However, this is also subjected to great Scientific debate. Just because there are smaller bones of a different species it won’t necessarily means it is in fact the prey. Let’s look at a living example. Poisonous snakes are relatively smaller than human and while we do act as predators, it is also possible for snake to be the predator. In the future if someone finds a skeleton of a human with a snake imprint nearby, it would be wrong to assume the snake has killed the human. This is because human also have the capability to prey upon the sake. This is where we get into the muddy areas of Paleobiology and Paleontology.


Please read the Paleobiological Hierarchy page for detailed observational information.


1. http://geolmag.geoscienceworld.org/content/96/1/1.abstract

2. Kathleen Nester, University of Calgary (Undergraduate Student)

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