May 10 Speaker: Dr. Bruce McFadden


The sedimentary sequence in Florida began in the Eocene during the Cenozoic period, which is Earth’s current geological era. The Pleistocene era, commonly known as “The Ice Age,” began approximately 2.6 million years ago and lasted until approximately 12,000 years ago, with megafauna, described as those species over 100 lbs., existing across the peninsula. Prior to the Pleistocene, volcanic activity created a series of islands between North and South America, which eventually coalesced to form the Isthmus of Panama, enabling travel between the continents during what has been termed the Great American Biotic Interchange (GABI).

Fossils of South American immigrants, such as giant ground sloth, glyptodonts, and giant armadillos can be found across much of Florida, including within our own local springs and rivers. Native megafauna such as horses, camels, llamas, zebras, saber-tooth cats, dire wolves, and mastodons roamed the plains of Florida at the beginning of the Pleistocene. In the areas where one can find fossils of tapirs and deer, the local environment is interpreted to have been heavily forested. Swampy areas contained alligators, as is the case in the present-day.

However, as the Pleistocene progressed, the types of megafauna began to diversify as new immigrants to North America, such as the Columbian mammoth arrived from Asia and Africa via the Bering land bridge, which allowed access to new territory approximately 1.8 mya. There are three theories of megafaunal extinction: climate cycles and failed adaptation, resource competition and selection, and the overkill hypothesis. Changing climate cycles could have resulted in the loss of vegetation upon which massive herbivores depended. Pressures on herbivores would, in turn, affect the viability of the carnivore population.

Mastodons and mammoths successfully coexisted across Florida, as their teeth were different, allowing the mammoths to graze on more grassy vegetation and the mastodons to browse on more shrubby vegetation. Once bison arrived approximately 500,000 years ago, and spread out across much of North America, stable isotope studies indicate that several types of grazers at that time, mammoths, horses, zebras, and bison, competed for the same resources--grass. A bison skull from the Wacissa River, with a projectile point embedded in its forehead, dated to approximately 13000 years ago, demonstrates direct interaction between megafauna and humans in Florida. A cast of this skull is on display at the Florida Museum. These topics and much more will be discussed and we hope you’ll join us either in person or by Zoom.

Dr. MacFadden is a distinguished professor at the Florida Museum, is director of the University of Florida Thompson Earth Systems Institute, and is a leading researcher in the fields of vertebrate paleontology and evolution. He received his Bachelor's degree from Cornell University and his Ph.D. in geology from Columbia University, with a specialization in paleontology.

Tuesday, May 10, 2022, 7 pm – 8 pm Eastern Time  IN PERSON: North Port Community United Church of Christ 3450 South Biscayne Boulevard. Our guest speaker, Dr. McFadden, cannot attend in person, but we still plan to meet live and have the presentation projected on the screen for a hybrid/Zoom Live meeting.

Image: Early Florida hunter stalking a bison, courtesy of The Bishop Museum of Science and Nature