Fossils from Florida, USA
E R Matheau-Raven (UK)
Florida has one of the world’s richest fossil deposits of both terrestrial and marine origin, encompassing over 2,000 known fossil locations. The state is famous for its Pliocene/Pleistocene fossil fauna but also has a rich and diverse Miocene heritage, plus its coastal waters abound with giant Carcharocles megalodon shark teeth, much prized by fossil divers for their value.
The Thomas Farm site in Gilchrist County, North Central Florida has the largest Miocene mammal deposits east of the Rocky Mountains. It was discovered in 1931 after locals reported what they thought was an Indian burial site and has, for the last 70 years, continually given up its secrets. The fossils from here are dated at 18 million years old and are typified by many types of mammal, such as the early three-toed horse Nanippus.
Florida began to form by a combination of volcanic activity and marine deposition along the northwest portion of Africa over 500 million years ago during the latter part of the Cambrian Period. At about 300 million years ago (during the Upper Carboniferous), the time of the formation of the supercontinent, Pangaea, Florida was sandwiched between what were to become North and South America and Africa. Near the Triassic/Jurassic boundary (210 million years ago), Pangaea began to divide into two major continents, Laurasia (North America, Europe and parts of Asia) and Gondwana (South America, Africa, India, Australia and Antarctica).
Later, as the Atlantic Ocean seafloor continued to spread, North America split from Laurasia and drifted away in a north-westerly direction, dragging the Florida Platform block with it. The marine environments of Florida during the early Cenozoic were part of the Tethys Sea, a circum-global seaway that allowed for the broad dispersal of many groups of organisms into new areas and unfilled niches.
During this period of submergence, the skeletons of marine invertebrates deposited onto the sea floor formed the limestone platform on which Florida now sits. Eroded terrestrial sediments from the north covered the Florida Platform forming islands, and eventually allowing for diverse habitats from dense forests to open grasslands. Diverse fossil beds stand as awesome testimony to the vast array of terrestrial life forms that migrated to Florida since its first documented emergence in the middle Oligocene (30 million years ago).
Many advances and retreats of the sea have occurred over the Florida area during the Cenozoic. Some parts experienced mass erosion by the advancing ocean. Deposition of sediments and invertebrates were often left behind by the retreating sea. Erosion of sediments and limestone by freshwater runoff created karst landscapes, known for sinkholes and caves. These would later become deadly traps for unsuspecting animals, resulting in some of the most prolific fossil sites in the world.
Migration of plants and animals between North and South America occurred during the Pliocene, some two to three million years ago. This great interchange was facilitated by the formation of a land bridge connecting the North and South American continents. The sudden appearance in the Florida fossil record of animal groups previously known only from South America testifies to this open exchange of terrestrial life forms. Llamas, giraffes, glyptodonts and tapirs are fairly common fossil finds in Florida.
Towards the end of the Pleistocene Epoch, 100,000 years ago, the last Ice Age took hold and sea levels dropped resulting in an expansion of Florida’s land area. At its greatest extent, it was almost three times its present size. At the end of the Ice Age, some 10,000 years ago, man arrived in Florida. Perhaps it is no coincidence that this episode went hand in hand with the rapid extinction of the large terrestrial animals.
Further reading
A wonderful book illustrating Florida’s fossils is THE FOSSIL VERTEBRATES OF FLORIDA, edited by Richard C Hulbert, Jr, University Press of Florida. First Edition February, 2001 and hardback with 384 pages, 341 drawings, and black and white photographs. ISBN 0-8130-1822-6.