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•They represent evidence of earlier life. •They are our only link to the living past. •They tell us of ancient environments and organism habits. •Many times they are used to help distinguish periods of geologic time. Fossils as Evidence For Evolution •First organisms were simple in structure •As time passed, life forms increased in size and complexity •The rock record shows that through time many organisms disappear and are replaced with new and different organisms •The evidence indicates a changing or evolving pattern of life forms •This process of change that produces new life forms over geologic time is called EVOLUTION Means “turned to stone.” Types of organisms fossilized: • Wood • Bones • Teeth • Shells How the process works: The original remains are replaced by minerals. We can learn about what the original organism looked like and reconstruct environments A shell is deposited in mud. The shell dissolved over time, leaving a cavity in the rock (and a good impression of itself). The cavity is the mold. The cavity later fills in with mineral substances. This forms a cast. Type of organism fossilized: Wooly Mammoth Body is preserved Some scientists think that DNA can be preserved •Original remains stuck in a sticky resin from the trees •Body of the insect preserved •Insects mostly •Tells us a lot about the organism The World Famous La Brea Tar Pits The Rancho La Brea Tar Pits is one of the world's most famous fossil localities, located 5 miles west of downtown Los Angeles. Near the end of the Ice Age, about 40,000 to 10,000 years ago, saber-toothed tigers and woolly mammoths roamed the Los Angeles Basin. Some of these animals, along with countless other animals and plants, became mired in pools of natural tar a tragic ending for many prehistoric creatures, but a boon for today's paleontologists studying the Ice Age. Any prehistoric animals and plants can be fossilized in tar. In the case of La Brea-bison, wolves, sloths, saber-tooth cats, and camels were found. The animals were trapped in the gooey tar and were preserved relatively unchanged. Trace fossils are the most common fossils found in nature. They are impressions left in the sediment from once living things. Common trace fossils are footprints or walkways, resting spots, living burrows, feeding burrows They are not the original parts of an animal. A trace fossil is preserved when mud or dirt that was disturbed by something living hardens and keeps its shape. They give valuable information ABOUT the size, height, weight of the organism. Trace fossil footprints of early humans are evidence that they walked upright. •Not an original organism. •Waste material from animals that has been petrified.(“Dino doodoo”) •Gives valuable information about what the organism ate. •A good index fossil must be easily recognized •A good index fossils must have been found over a wide geographic area •A good index fossils must have been limited in geologic time. The organism existed for only a short period of geologic time •Many species of trilobites are good index fossils In the summer of 1858, Victorian gentleman and fossil hobbyist William Parker Foulke was vacationing in Haddonfield, New Jersey, when he heard that twenty years previous, workers had found gigantic bones in a local marl pit. Foulke spent the rest of the summer directing a crew of hired diggers shin deep in gray slime. Eventually he found the bones of an animal larger than an elephant with structural features of both a lizard and a bird. First Nearly-Complete Dinosaur Skeleton Foulke had discovered the first nearly-complete skeleton of a dinosaur -- an event that would rock the scientific world and forever change our view of natural history.