Metal Collector Duo Goes Diving in Florida River, Uncovers Treasure House of Fossils in a Sinkhole

A duo of collectors have uncovered a treasure house of fossils in Florida. The discovery was made while diving in the Steinhatchee River in 2022, stated Science Daily. Robert Sinibaldi and Joseph Branin were surprised by the findings because visibility issues make it difficult to locate anything in Steinhatchee waters. The duo shared about the remains with the Florida Museum of Natural History. The importance of the remains further stunned them after they were informed of the analysis by the museum authorities. Details regarding these fossils were published in MDPI. 

All the remains were uncovered from an ancient sinkhole. In total, 552 fossils have been recovered so far from the site. The remnants primarily belonged to the relatives of horses, sloths, and armadillos. Paleontologists after examinations claimed that many of the remains were preserved in the middle Irvingtonian period, falling in the Pleistocene ice ages. This information was huge for experts as fossils from the period are a rarity.  "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," Rachel Narducci, vertebrate paleontology collections manager at the Florida Museum and coauthor of the study explained. Before the Steinhatchee River finding, researchers had found fossils from this period only at one another Florida site.

Three-quarters of the remains were found to be of the caballines, an early species from a subgroup of horses. They are ancestors of domestic horses and their wild relatives. "That gives us a good sample size to measure or make comparisons, and it also tells us a little bit about the environment," said Richard Hulbert, lead author of the paper and retired Florida Museum vertebrate paleontology collections manager.

Researchers also noted a tapir skull in the collection. The remnant had a combination of features, that had never been seen before together. Despite the unique characteristics, Branin did not want the creatures to be classified as a new species. "We need more of the skeleton to firmly figure out what's going on with this tapir," he said. "It might be a new species. Or it always could just be that you picked up the oddball individual of the population."

Though experts don't have many specimens from the middle Irvingtonian period in their custody, they have several fossils before and after that period. From that fossil record, they have been able to determine that certain species from the early Pleistocene have gone extinct, while some appeared for the first time during the late Pleistocene. Researchers have also observed that certain species went through changes in features like body size and shape from the early to late Pleistocene period.

One of the animals in which these transformations were noted, belonged to the now-extinct genus Holmesina. The group resembled modern armadillos in appearance. They first appeared in the fossil record two million years ago and were classified to be a part of the Holmesina floridanus species. These individuals weighed around 150 pounds. As time went on the creatures grew larger and heavier, till they were classified as Holmesina septentrionalis at an average weight of 475 pounds. "It's essentially the same animal, but through time it got so much bigger and the bones changed enough that researchers published it as a different species," Narducci added. The remains of this group of animals were located in Steinhatchee waters. 

Researchers noted that remains of this group from the middle Irvingtonian period had ankle and foot bones aligning the size of the larger H. septentrionalis species, but other features resembled the older, smaller H. floridanus species. "This gave us more clues into the fact that the anatomy kind of trailed behind the size increase. So, they got bigger before the shape of their bones changed," Narducci explained. As per observations, experts determined that skeletal features developed later to support the increasing weight. Excavation of the site is still ongoing, with more fossils hopefully to be recovered, according to researchers.