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The study of fossils, Paleontology, assists scientists in learning about the EarthÕs history. According to Webster a fossil is a remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth's crust. The study of fossils can tell something of the living conditions or feeding habits of the preserved creature. Fossils provide direct evidence of life in the distant past. This evidence is useful in the interpretation of anatomical features and for the relationships of living organisms. Anyone with a hammer, some knowledge, respect for the property of others and the law can make discoveries that may be useful for expanding our knowledge of EarthÕs history.
This is how a fossil forms. The animal dies. The soft fleshy parts deteriorate. The bones and teeth that remain eventually are covered with sediment season after season. The bones and teeth are surrounded by silt and mud begins to turn into stone from the minerals in the sediment. This process takes millions of years. The new rocks containing the bones and teeth are worked up to a dry surface so that they can dry out. Fossil hunters then discover these.
Most fossils are made of the hard parts of an organism, fossils of soft-bodied organisms can be found under very special conditions. These are very unusual circumstances.
How are fossils found? Many states have regulations regarding the hunting of fossils. You can check to see what requirements are needed by asking at a state park or by looking up the information per state on the Internet. Florida has a form that can be filed out on-line. Ohio has forms available at most of the state parks.
Look for fossils where there has been a stretch of hill removed, such as along a highway. This is like taking a ride in a time machine or looking back in time through a special telescope. Carefully examine the rocks that are jutting out of the exposed hillside. There may be plant or animal fossils embedded in these outcroppings.
Another good place to look for fossils are along the banks of streams and creeks. Here are places that ancient animals may have frequented to drink or hunt. Clues to their habits may remain in the soil that later solidified into stone. Use a length of wood or metal rod to probe the soft soil. When you hit something solid you can start to gently remove the layers of soil above the embedded object. You may find a bone or an impression that has been fossilized.
Recently scientists are using satellites to search the Gobi Desert for rare and valuable fossilized specimens. In 1993, Mike Novacek and a team of researchers from the American Museum of Natural History found a huge amount of fossils in Ukhaa Tolgod. Each summer these scientists would travel back to search for more fossils. It was a difficult task given the unrelenting nature of the Desert. By using satellite images the scientist located areas that showed places in the Gobi Desert that were most likely to harbor the ancient specimens such as skeletons of Velociraptors, several species of dinosaur embryo fossils, hard-to-find fossils of the bird-like Mononykus, and skulls of Mesozoic mammals.
For most purposes using satellite imaging is probably not an option. The typical fossil hunter has other hazards to avoid. Be warned there are fossil protectors! A park ranger may ask to see your permit for fossil hunting. Some fossil protectors are not human at all. While fossil hunting in humid, moist areas, be aware of snakes, alligators, or other harmful insects or animals. There are other things to look out for as well, be aware of sharp objects that possibly litter the areas as well.
Fossils are useful for telling about the age of the Earth. Fossilized rocks can be used as a suggestion of the age of rocks and to provide correlations between rocks of the same age over extensive geographical areas. Fossilized rocks also help in the reconstruction of the past composition of the continents by the correlation of organisms on now-separated continents.
What are living fossils? What a concept! ArenÕt all fossils of extinct animals or plants? Up until about 150 years ago, that is what scientists thought. Then along came Charles Darwin. He coined the term Òliving fossilsÓ. In his Origin of Species he called lungfish and other species whose form remained unchanged since its inception Òanomalous formsÓ that may be Òcalled living fossils.Ó Since that time there have been many other living fossils identified. Webster defines a living fossil as an organism such as the horseshoe crab or a ginkgo tree that has remained essentially unchanged from earlier geologic times and whose close relatives are usually extinct.
The Dawn Redwood Tree (Metasequoia glyptostroboides), is an example of a living fossil. These smallest of the giant Redwood Trees were thought to be extinct until living specimens were discovered in the 1940s. Both branchlets and leaves grow out in pairs from points along the stem. The bright green, feathery leaves turn reddish brown and drop to the ground in autumn and reappear fresh and green in the spring. Since being found several seeds and cuttings have been transplanted from its native habitat in Central China to areas around the world.
Many times during EarthÕs history there have been great extinctions. The causes of these great extinctions are at best uncertain. Volcanic eruptions, drastic climate changes, universal disease, or comet or asteroid collisions have all been suggested by scientists as possible causes of great extinctions. One of the great extinctions took place when the dinosaurs vanished 65 million years ago. Another took place just before the dinosaurs appeared 245 million years ago when almost ninety percent of the EarthÕs species died out.
This leads us to ask why didnÕt these plants or animals become extinct like itÕs near relatives? During the Cambrian Explosion there were a host of new creatures flourishing. One of them was the trilobite, the state fossil of Ohio. The trilobite became extinct 245 million years ago, while other arthropods thrived. Fossil evidence shows that one early arthropod, the horseshoe crab, developed at the same time as the trilobite. Three hundred million years ago, the horseshoe crabs were at their peak. The species of horseshoe crab that lives now differs very little form the horseshoe crabs of the Carboniferous Period. The horseshoe crab is not a crab at all. True crabs belong to a family called crustaceans. These crabs scurry across the sea floor and hide in crevices and hollows. Horseshoe crabs more closely resemble pill bugs. The horseshoe crab swims using tiny legs that flail at the water from underneath an armored shell.
Fifty million years after the Cambrian Explosion, trilobites feared nothing in the sea! Then along came the nautilus just over 500 million years ago. The nautilus had hard shells and sharp beaks. They were relatives of the octopus and the squid. At first the nautilus had long shells that looked like dunce caps. Later species developed spiral shells. The spiral shell protected the soft body of the nautilus with only the tentacles, beak, and eyes protruding out of the shell. As time passed, new animal species learned to defeat the defenses of the nautilus. To avoid predators, the nautilus dove deeper into the seas. Nautilus spent their days thousands of feet down in the ocean where swimming reptiles couldnÕt follow.
Another living fossil is the crocodilians. Both crocodiles and dinosaurs first appeared in the Triassic Period, about 245 million years ago. Early crocodiles defended themselves with sharp spikes and ate plants, but most species were predators. Twenty-two crocodilian species live in the rivers and swamps of the world today and are the largest reptiles on Earth. These prehistoric survivors are almost identical to species that lived 100 million years ago.
A few crocodiles live in southern Florida, but alligators rule in the Americas. Alligators differ from crocodiles in two ways: they tend to have broader snouts, and their teeth are relatively even. Alligators, unlike crocodiles, rarely tend to eat people.
Why did the crocodilians survive? Scientists suggest that crocodilians survived a catastrophic event because they are cold-blooded. Crocodilians could conserve food and outlast larger warm-blooded dinosaurs. Add to this that while crocodilians are resting underwater, crocodilian hearts beat only 3 or 4 times per minute, so it can conserve oxygen. Crocodilians burn very little energy, so they need little food. All these special adaptations helped the crocodilians survive into the current time.
Here is where there is some debate on living fossils! Some speculate that these animals survived because they were most able to adapt to the changing environment around them and thus survived to the present time. There are those who believe that these animals and plants werenÕt stronger or smarter than other animals, they were simply most able to survive.
Mark Renz (1999) Fossiling in Florida University of Florida Press
T.S. Kemp (1999) Fossils & Evolution Oxford University Press
Clare Milsom and Sue Rigby (2004) Fossils At a Glance Blackwell Publishing Co. Victoria, Austrailia
James Martin (1997) Living Fossils Crown Publishers Inc.
Jan A. Pechenik (2000) Biology of the Invertebrates McGraw-Hill
Doyle, P. (1996) Understanding Fossils. An Introduction on Invertebrate Paleontology. Wiley, Chichester, UK.
Prothereo, D.R. (1998) Bringing Fossils to Life: an Introduction to Paleobiology. W.C.B./McGraw-Hill, New York.
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