Paleontology exercize a great fascination on the people and the information attached to a fossil is extremely rich and atractive. Fossils are precious records of ancient ages. Their preservation requires a well defined set of conditions without which dead animals and plants would otherwise have been completely decomposed. Dead organisms are buried by mud at the bottom of water bodies or by sediments carried to the sea. Although the soft parts of their bodies soon disappear, bones, teeth, shields, shells and wooden fragments may take longer to decompose. When buried under low oxigen conditions, they can be preserved in sedimentary rocks for millions of years. Another type of fossil record is that left by footprints or burrowing worm.