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The Pre-History of Florida

Relatively little is known about the history of Florida during the Paleozoic Era (550-225 million years ago). Most geologists agree that Florida, along with the rest of the southeastern United States and Mexico, were part of the super-continent of Gondwana. Gondwana included Africa, South America, Australia and Antarctica along with parts of Europe and Asia. At the same time, North America, Europe and Asia were combined into another super-continent called Laurasia. About 300 million years ago these two land masses collided forming one great super-continent called Pangea. Florida was in the middle of this huge landmass, thousands of miles from any ocean.

In the early Mesozoic Era, during the Triassic Period (225-190 million years ago) Pangea began to break apart through a process called rifting. Rifting stretches continental crust until it breaks, and causes earthquakes and volcanic eruptions. As Pangea separated, rifting began in a northeast-southwest line running from Charleston, South Carolina through Savannah, Georgia to an area near the Apalachicola river in the Florida panhandle. If rifting had continued in this area, then most of Florida and part of Georgia would have separated from North America along with South America and Africa. In the early Jurassic Period however, rifting shifted to an area east of the Bahamas and stopped in Georgia and the Florida panhandle. By about 175 million years ago the newly opened Atlantic Ocean and Gulf of Mexico were between Florida and the other continents. Throughout the Triassic, Jurassic and even into the early Cretaceous Periods, about 125 million years ago, much of northern Florida remained above sea level and probably would have been inhabited by dinosaurs, however, no dinosaurs fossils have been found since the rocks that would contain them are deeply buried beneath younger deposits. Rising sea levels during the Jurassic would have submerged the southern part of Florida by midway through the period and by the mid-Cretaceous, Florida, along with the southern half of Georgia and Alabama, were underwater.

For nearly the next 100 million years Florida remained submerged. In the Oligocene Epoch about 30 million years ago, when global cooling caused sea levels to fall, northern Florida emerged from the sea. The oldest known fossils of terrestrial vertebrates were found near Gainesville and date from this time. Later in the Oligocene sea levels rose and Florida was submerged once again. Sea levels fluctuated considerably over the next 24 million years and at times of higher sea level, much, if not all, of Florida was submerged. At other times the sea was close to modern levels and parts of the northern peninsula and panhandle were emergent. During the Miocene Epoch (26-5 million years ago) the South American plate was again drifting north, slowly uplifting the southern peninsula. This, along with sands and clays eroded from the Piedmont highlands of central Georgia and Alabama, created what is now south and central Florida. By the Pliocene, North and South America were joined by the Panamanian Isthmus, disrupting ocean currents and causing widespread continental glaciation to begin. The last major sea level high stand was 4.5 to 2.5 million years ago, when Florida was submerged for the last time in geologic history.

The next 2.5 million years are know as the Ice Age. Continental glaciers had advanced and retreated many times from the poles, at times covering all of Canada and the northern United States. Ice piling up on the continents caused sea levels to fall as much as 400 feet. Florida, in these times of glaciation, had a climate similar to that of Virginia today, with annual snowfall. With lower sea levels, Florida was more than twice as wide as it is today. St. Petersburg would have been more than 75 miles from the Gulf of Mexico during this time. What is now Tampa Bay, and far beyond, would have been a combination of palmetto landscape, grassy plains and woodlands, dotted with lakes and crossed by winding rivers. For animals seeking refuge from the bitter cold of the north, Florida was a welcomed haven. Between times of glaciation, the sea level and climate were close to that of today. During this time Florida’s wildlife would have included: antelope, bears, bison, deer, gi ant beavers, giant armadillos, ground sloths, glyptodonts, horses, lions, llamas, mammoths, mastodons, peccaries, saber-tooth cats, tapirs, wolves, alligators, crocodiles, and many others.

Man first inhabited Florida during the last period of glaciation, about 10 to 15 thousand years ago. Many Paleo-Indian artifacts have been found in Florida. These Florida natives developed several sophisticated cultures and thrived up until about 500 years ago when the Spanish explorers arrived. None of these native peoples or their cultures survived this encounter. In the last 12,000 years there has been a mass extinction of many of the megafauna (large vertebrate animals weighing more than 100lbs) not only in Florida, but throughout North America and in some cases, worldwide. There are several schools of thought on the cause(s) for these extinctions. One opinion is that these animals were unable to adapt to the climate changes at the end of the last glaciation period and subsequent changes in vegetation. Another opinion is that proficient human “big-game” hunters caused the animal populations to drop below a sustainable level. Some believe it was a combination of th e two, while others think disease played a role. We may never know the answer to this mystery, but surely the world is a poorer place with their loss.

The Tampa Bay Fossil Club invites you to join us in our quest for knowledge of the pre-history of Florida. Join us on field trips as we hunt for the fossils from the long lost creatures that once inhabited our area. Meet with us monthly as we discuss and ponder the mysteries that pre-historic Florida poses. Join us!

Written by Robert Page
Director, TBFC

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