Fossils:

Louisiana Geological Survey 208 Howe-Russell Geoscience Complex Baton Rouge, Louisiana 70803 Tel: 225 578 5320 Fax: 225 578 3662 1934 Fossils, the preserved remains or evidence of past life, are the only direct means of documenting the history of life on the Earth. Fossils range in size from the microscopic shells of amoeba-like organisms known as foraminifera to the bones of 30 meter-long dinosaurs. The most common fossils are marine organisms, those that lived in the oceans, because oceans cover over 70% of the earth and provide a more suitable environment for fossil preservation than most environments on land. Specialists known as paleontologists study these glimpses into the past in order to unravel this planet’s long and intriguing development of animals, protists (simple one-celled organisms), and plants (Pojeta and Springer, 2001). Exposed strata or sediments where fossils may be recovered are known as fossiliferous outcrops. Such outcrops are rare in Louisiana for a variety of reasons. Outcrops exposed by road construction or by natural means will often be covered quickly by the state’s abundant vegetation. Furthermore, in a geological context, the surface exposures of Louisiana are very young in age, and this affects the number and diversity of fossils. Examination of the Geologic Map of Louisiana (Snead and McCulloh, 1984) reveals that the oldest surface sediments are Cretaceous in age (approximately 70 million years old). These sediments are rare and occur only around salt domes where the strata have been pushed to the surface. The vast majority of surface exposures in Louisiana are Tertiary and Quaternary in age (less than 65 million years old); many of the sediments are even younger (less than 10,000 years old). This is in contrast to some states that have surface exposures that span hundreds of millions of years. This immense amount of time increases the probability of finding extinct organisms as well as a greater diversity of fossils. Also, large portions of the surface sediments in Louisiana were formed as parts of rivers, ancient deltas, and swamps. These terrestrial and transitional environments, which were common in the geologic past in Louisiana, are not nearly as conducive for the preservation of fossils as the marine environment. Therefore, these factors cause marine fossils to be relatively uncommon in the surface exposures in Louisiana. 46-MILLION-YEAR-OLD MARINE