Tuesday, June 28, 2011

Working with extinct animals: Basics (1): Fossils

To work with extinct animals, certain basic knowledge needs to be understood.

Paleontology is the study of the ancient history of the earth.  As a descriptive science, paleontology tries to explain what happened in the prehistoric past.  Like historians, paleontologists reconstruct what the facts were.  As scientists, they form theories as to what life was like.  They then seek to see if their theories of ancient life match what is in the fossil record.

To reconstruct ancient life, paleontologists study various things.  They look at fossils of plants and animals.  Also paleontologists examine ancient pollen from plants, rock formations, the rocks themselves, and ice cores from glaciers.  (Building a picture of the ancient earth requires the knowledge from an array of sciences - botany, biology, climatology, ecology, geology, and zoology.)  In addition, paleontologists may specialize by studying a life form such as dinosaurs or early plants or by reviewing an extinction event of a particular age.

Making Fossils
The fossil record that paleontologists rely on is the sum total of fossils and their occurrence in the rock formations.  The fossil record cannot show everything, since many living things do not form fossils.  However, paleontologists can discern some things about prehistoric life from what they do find.

The things that do turn into fossils are bones, fish scales, pollen, shells, and teeth.  Other fossils can be footprints, plant imprints, animal burrows, and trails of invertebrates.  In addition, some plants and animals become encased in tree amber, while others become flash frozen as mummies like mammoths.
Many fossils are made through the process of decay, burial, recrystallization, and compression.  The organism dies and is buried in a streambed or lake.  As the body decays, the water brings in more layers of silt on top of it.  Eventually, the silt builds up and the layers become compressed into sandstone.  Some fossils may become recrystallized with a mineral replacing the body’s original minerals (such as calcium in bones).  Still other fossils become a cast or a mold of the organism itself.

Fossil Types
Most paleontologists focus on body and trace fossils for study.  Other types of fossils are “microfossils” which are fossils that can be only examined by a microscope.  “Resin fossils” are organisms found in amber.  “Living fossils” are species which are unchanged from prehistory such as the lobe-finned coelacanth.
The fossils that most people picture are the body and trace ones.  “Body fossils” are the bones, scales, shells, and teeth of the organism.  They come from the body of the organism itself.  For example, dinosaur skeletons are full body fossils.

“Trace fossils” are more subtle since they are things like footprints and tailprints.  Burrows and trails of invertebrates are usually the only thing that is left behind of them.  Eggs, nests, and fecal droppings (coprolites) are considered to be trace fossils as well.  Together, these fossils give an impression of how the organism lived.

Fossils tell much about life of the prehistoric past.  They can tell about the climate of an area, what plants grew there, and what type of animal the organism was.  Teeth will tell whether the animal is a meat eater or plant eater.  Footprints tell the gait and speed of the animals.  Some fossils have impressions of feathers, hair, or leaves to indicate what the organism looked like.  The grouping of fossils in one place can indicate the social structure of the animals, whether they were predator or prey, or how they ended up together (such as a great flood).  The fossil skeleton will often tell what species of the animal was, how large, the age, and sex.  In addition, the fossil itself can give clues to any major catastrophic event of the past.

Works Used
Little, Richard, “Dinosaurs, Dunes, and Drafting Continents: the Geohistory of the Connecticut Valley”, self-published, Hartford, CT, 1986.
Turner, Alan, “National Geographic Prehistoric Mammals”, National Geographic Society, Washington D.C., 2004.
Various, “Prehistoric Life”, Dorling Kindersley, New York, 2009.

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