Article and photos by Mark Renz
"It may have been a Miocene cold snap that killed them," said Gary Morgan, then senior biologist of vertebrate paleontology at the Florida Museum of Natural History in Gainesville. "We really don't know for sure."
The year was 1994, and Morgan was referring to the remains of a nearly complete 10-million-year-old sea cow called a dugong (cousin to the manatee) and several partial skeletons, buried at the same level in a Polk County, phosphate mine. Miocene is the period in Florida's past that stretches forward from 24.5 million years to 5 million years ago. The sea cow site, near the town of Bowling Green, was actually the southern tip of Florida 10 million years ago.
As an amateur paleontologist, I had stumbled upon the dugong remains in the walls of a phosphate mine operated by Cargill Fertilizer Company. Miraculously, the first skeleton exposed had only been grazed by the huge claw of a dragline bucket. It destroyed most of the ribs on one side as well as many of the tail vertebrae. Each remaining rib and vertebra, as well as the crushed skull, had to be wrapped in aluminum foil or a plaster jacket for stability before being removed.
"The dugongs may have died in a coastal lagoon or estuary, perhaps between barrier islands and the coast," said Morgan. "The water was probably about 20 feet deep at the time. We're standing 125 feet above sea level right now, so that means the ocean would have been 145 feet higher than it is today."
Miocene dugongs resembled manatees, but their tails were V-shaped like a whale's, rather than the round paddle-style seen on the manatee. Dugongs are still alive in Asian waters but became extinct in Florida about 2 1/2 million years ago, the same time manatees were beginning to show up in the fossil record. Metaxytherium floridanum is the extinct Florida genus and species.
Barbara Toomey and her son Jim spent several weeks excavating the remains, which were turned over to the Florida Museum of Natural History and now on permanent loan to the Clewiston Museum. (click here)
Today, the mine has been reclaimed and there is grass growing over the site where dozens of ancient sea cows once lived and died.
Cargill used their light equipment to scrape off the overburden. Then a volunteer crew led by Barbara and Jim Toomey, began the subsequent steps. A three inch layer of cement-like clay had to be broken through with a pick-axe, followed by small garden trowels and then dental picks.