A Florida Sink Gap Swallowed These Animals 500,000 Years In the past—Now Their Bones Reveal a Misplaced World

Round 500,000 years in the past, some horses, sloths, and armadillos had a really dangerous day—they fell right into a sinkhole in what’s now Florida and remained there till two males found their bones in 2022.

Fossil hunters Robert Sinibaldi and Joseph Branin found 552 exceptionally preserved animal fossils whereas diving within the Steinhatchee River. The findings, detailed in a study printed late final 12 months in Fossil Research, make clear a little-known interval of the Pleistocene ice ages referred to as the center Irvingtonian.

“It’s like diving in espresso,” Sinibaldi mentioned of the murky Steinhatchee River in a statement from the Florida Museum of Pure Historical past. Branin first noticed horse enamel, which then led to the invention of many different specimens, together with the cranium of a tapir (giant pig-shaped herbivorous mammals nonetheless alive right now). “We knew we had an necessary web site, however we didn’t understand how necessary,” Sinibaldi added.

In line with the examine, the unlucky animals met their demise in a sinkhole, the place their stays had been preserved beneath layers of accrued sediments for tons of of 1000’s of years. Again then, the Steinhatchee River doubtless wasn’t the place it’s right now. As erosion reshaped its course, the river finally collided with the sinkhole, washing the fossils into the riverbed.

Sinibaldi and Branin submitted their findings to the Florida Museum of Pure Historical past, the place paleontologists confirmed their thrilling origins.

“The fossil report in every single place, not simply in Florida, is missing the interval that the positioning is from — the center Irvingtonian North American land mammal age,” mentioned Rachel Narducci, vertebrate paleontology collections supervisor on the Florida Museum and a coauthor of the examine. Actually, it’s solely the second identified center Irvingtonian web site in Florida.

An absence of fossil proof from this obscure time interval has left many questions unanswered concerning the evolutions of sure animals. For instance, Holmesina floridanus—now-extinct creatures that appeared like giant armadillos and weighed a median of 150 kilos (68 kilograms)—developed right into a a lot bigger species named Holmesina septentrionalis, the place people had been round 475 kilos (216 kg). Holmesina‘s ankle and foot bones from the Steinhatchee River fossils now present perception into this transition, as they showcase options of each H. floridanus and H. septentrionalis.

“This gave us extra clues into the truth that the anatomy sort of trailed behind the scale improve. So, they received greater earlier than the form of their bones modified,” Narducci defined.

Sinibaldi and Branin’s discovery additionally presents clues about what modern-day Florida could have appeared like half one million years in the past. An awesome majority of the fossils are of caballines, an early group of each domesticated and wild horses. Since horses developed to stay in open habitats, and given their prevalence inside the Steinhatchee River fossils, the researchers counsel that Florida was additionally as soon as an open panorama with fewer bushes than right now.

“What was nice concerning the horses from this web site is, for the primary time, we had people that had been full sufficient to indicate us higher enamel, decrease enamel and the entrance incisors of the identical particular person,” mentioned Richard Hulbert, the lead writer on the paper and a retired Florida Museum vertebrate paleontology collections supervisor. The wear and tear on well-preserved enamel might additionally present clues on what sorts of vegetation these early horses had been consuming.

Moreover, an uncommon tapir cranium uncovered alongside the riverbed would possibly signify a brand new species—or might simply be “an oddball particular person of the inhabitants,” Hulbert defined. “We want extra of the skeleton to firmly determine what’s happening with this tapir.”

The findings be a part of a rising listing of vertebrate fossil websites in Florida found by passion fossil hunters, highlighting the potential for profitable collaborations between passionate amateurs {and professional} researchers.