This Underwater Fossil Bed Found In Florida Contains Animals From An Obscure Part Of The Ice Age
About half a million years ago, several sloths, armadillos, and horses fell into a sinkhole in Florida’s Big Bend region.
Of course, they were unable to get out of the sinkhole and died. Over time, it was filled with sediment, preserving the animals until a pair of fossil collectors discovered them in 2022.
For years, Robert Sinibaldi and Joseph Branin have been diving near Sinibaldi’s property on the Steinhatchee River, combing the riverbed for fossils. Since the water is full of tannins, it’s hard to see through.
In June 2022, they were on one of their regular fossil hunting trips when Branin looked down and happened to spot horse teeth.
They continued digging around and uncovered a hoof core and a tapir skull. More and more remains surfaced, with many of them in excellent condition.
“It wasn’t just quantity, it was quality,” said Sinibaldi. “We knew we had an important site, but we didn’t know how important.”
At the time the fossils were preserved, the Steinhatchee River probably followed a different course. But throughout the next thousand years or so, the river edged closer to the sinkhole until it recently eroded into the pit and exposed the fossils along the riverbed.
The pair shared their discoveries with the Florida Museum of Natural History. Paleontologists determined that the fossils were preserved during the middle Irvingtonian, an obscure period of the Pleistocene ice ages.
“The fossil record everywhere, not just in Florida, is lacking the interval that the site is from—the middle Irvingtonian North American land mammal age,” said Rachel Narducci, a co-author of the study and vertebrate paleontology collections manager at the Florida Museum.
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Until now, there had only been one other site in Florida with fossils from this time period, so experts don’t know much about it.
Some species went through changes in body size and shape during that gap. One of these species includes the now-extinct genus Holmesina, which resembles modern armadillos but larger.
Holmesina floridanus first appeared in Florida two million years ago. Individuals averaged 150 pounds and became larger over time. Eventually, a new species called Holmesina septentrionalis was classified, which grew up to 475 pounds.
The fossils recovered from the Steinhatchee River site provide a glimpse into how this process occurred. The ankle and foot bones matched the size of the larger H. septentrionalis, while retaining the features of the smaller H. floridanus. It seemed that the animals’ bones only evolved later on to help support their heavier body weight.
So far, a total of 552 fossils have been recovered from the site. About 75 percent of them belong to an early species of a subgroup of living horses that includes the domestic horse and its wild relatives.
Horses are adapted for living in open environments. Since there were so many horse remains at the fossil site, researchers can conclude that the area used to be fairly open instead of the heavily wooded landscape it is today.
The teeth were well-preserved, giving researchers the opportunity to study the diet of early horses.
Furthermore, a tapir skull with a unique mix of features was found. Experts were reluctant to designate it as a new species, though. More of the skeleton is needed to figure out why it is the way it is.
Fossils will continue to be collected from the site, but the process is slow because of the challenges of excavating an ancient underwater sinkhole.
The new study was published in the journal Fossil Studies.
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