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WHAT IS A FOSSIL?
Fossils are the remains of prehistoric life or some other direct evidence
that such life existed. The word "fossil" means "dug up", but usually refers
to plants or animals that have become petrified, or "turned to stone". We
usually think of fossils as impressions of ancient life encased in rock,
but this explanation is too simple not all fossils turn to stone. There
are many different types of fossils and processes of fossilization. |
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TYPES OF FOSSILIZATION
Fossils are created in many different ways, under
many different conditions. Some processes are unique and extremely specialized.
The most common types of fossilization are mold and cast fossilization,
mineral replacement (petrification), amberization, mummification, and
trace ossilization.
Molds and Casts
Most fossils are formed by the process of mold and cast replacement. When
an animal dies, it becomes buried in the ground, covered by sediment.
The remains of the animal EVentually dissolves away so that only a cavity
is left behind a natural mold. Later, dissolved substances may fill in
the cavity, forming a natural cast of the original animal. This type of
fossilization is easily the most common type of fossilization, found all
over the world. There are literally billions of mold and cast fossils
preserved in the Earth's crust.
Mineral Replacement (Petrification)
This takes place when water dissolves the original hard parts of plants
or animals and replaces them with mineral matter. It may happen so slowly
that the new mineral matter duplicates microscopic structures in the shell,
coral, wood, bone, etc. This type of fossilization produces some of the
most complete and detailed fossils ever found. Some petrified wood is
so well preserved that bark patterns, growth rings, and internal cellular
structures are all still intact.
Amberization
Amber, simply put, is ancient tree sap that has turned to stone over time.
Scientifically, amber is the resin of certain trees that has fossilized
over millions of years. It is a light, organic substance that is usually
yellow or orange in color and often transparent. It is formed by trees
exuding resin, usually through breaks or cuts in the bark. Once the resin
is expelled, it hardens and drops to the ground. It is eventually buried
in the dirt at the base of the tree and hardens further. Over the next
few thousand years, this resin is called COPAL, which is still soft and
essentially unfossilized. Copal is usually much younger in age than true
amber, and is much less desirable to jewelry makers and collectors. Copal
that is preserved in sandstone will eventially become amber over time
Copal that is preserved in clay will take much longer to fossilize. This
transformation is called "amberization", and is an ongoing process
that takes millions of years. At this point, this inert resin is considered
to be true fossilized amber.
Mummification
Occasionally, and animals die under extreme conditions for perfect
preservation in dry, undisturbed caves or frozen in glaciers, for example.
In these rare circumstances, hair, skin, blood, etc. can be preserved
with a minimum of cellular change. The most well known examples of this
type of fossilization are the frozen Mammoths of Alaska and Siberia. Complete
animals have been discovered fully intact, with internal organs preserved.
Mammoth meat is still consumed by the locals tens of thousands of years
after the last Mammoth walked the Earth!
Trace
Fossils
Trace fossils are not fossils of actual animals, but fossils of their
"traces". Some examples of trace fossils are footprints, trails,
burrows, borings, coprolites (fossil poop), etc. These are not actual
fossil animals, but simply residual evidence that these animals once existed.
Dinosaur tracks are some of the most famous types of trace fossils.
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FOSSIL TYPES AND LOCALITIES
Many types of plants and animals have been extensively preserved in the
fossil record. The distribution of these fossils encompasses the entire
Earth's surface, including areas on all seven continents. Here are some
of the more well known fossil localities
from around the world:
Plants
The Eastern United States and Europe have extensive coal fields where
ferns and related plant fossils are found in abundance. Individual deciduous
leaves are common finds in Colorado and Utah. British Columbia also has
a wide variety of fossil leaves. Large sections of petrified wood are
found in Arizona, and Patagonia is famous for its fossilized pinecones.
Invertebrates
The Burgess Shale locality in British Columbia is probably the
most famous invertebrate fossil site in the world. Trilobites, extinct
threelobed arthropods, are found in many localities around the world,
such as Europe, Australia, China, Canada, and Utah. Some of the best preserved
examples come from Morocco, Russia, and Oklahoma. Ammonites, related to
the modernday Nautilus, are famous from Europe and Madagascar, and are
also found in Russia, South America, and even the United States. Insects
in amber are commonly found along the Baltic Coastline and the Dominican
Republic. Crinoids are unusual animals related to starfish and sea urchins.
One of the most prolific areas for these fossil "sea lillies"
is Crawfordsville, Indiana, although crinoids have been discovered in
China and Australia.
Vertebrates
Dinosaurs are the world's most popular fossil vertebrates, and their fossils
are most commonly found in the Western United States and Canada. Dino
remains are also known from Europe, Africa, Argentina, and China. Aquatic
reptiles, such as Mosasaurs and Plesiosaurs have been found in England,
Morocco, Kansas, and Texas. Mammals, both large and small, are commonly
exposed in the Badlands area of South Dakota and Nebraska. Alaska and
Siberia are famous for beautifully preserved Mammoth fossils, ranging
from teeth and tusks to complete animals. Fossil fish are relatively common
in the fossil record. The Green River Formation of Southern Wyoming is
world famous for both its variety of species and its sheer number of specimens.
Complete fossil fish are also known from Europe, Lebanon, Brazil, and
China. Shark fossils, especially teeth, are found all around the world.
Some of the more well known fossil shark localities are the Eastern Seaboard
of the United States, Chile, and Morocco.
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