2 Miocene-Aged Fossil Sites in Florida

The University of Florida Museum list 9 Miocene-aged fossil sites in Florida. By contrast there are no significant Miocene-aged fossil sites in Georgia. However, animals that lived in Florida also occurred in Georgia because the same habitats–subtropical forests and woodlands–prevailed over most of North America during the Miocene era, a period of stable warm climate. The Miocene lasted a long time from 25 million years BP-5 million years BP, but this division of time is an artificial human construct. Species that lived during the early Miocene were completely different, though often ancestral, to those that lived in the later Miocene. Therefore, I chose to examine the lists of Miocene species that occurred at 2 different sites with fossils separated in age by over 10 million years. Both sites are located northwest of Gainesville, Florida and are about an hour drive from the Georgia border. Certainly, these species lived in Georgia as well.

Fossils from the Thomas Farm site are estimated to be 18 million years old or early Miocene. The site was discovered in 1931 when Raeford Thomas dug a well into an ancient sinkhole. Clarence Simpson of the Florida Geological Society looked through the dirt dug up from the well-drilling and was the first to catalogue fossils at the site. The site has been studied off and on ever since, and scientists consider it the best North American Miocene-aged site east of the Mississippi. Paleontologists list 1 species of fish, 12 species of amphibians, 23 species of reptiles, over 27 species of birds, and 40 species of mammals from the fossil evidence left here. Most notable among the reptile fossils are an extinct boa constrictor (Boa barbouri), and an extinct alligator (Alligator olseni). Boa constrictors are now restricted to southwestern North America south to South America, but they were widespread across North America during the warmer Miocene. Olsen’s alligator was somewhat smaller than modern alligators. None of the bird fossils found here have been diagnosed to the species or even genus level. Scientists are unfamiliar with birds from this era, and they can only diagnose the specimens down to the family level. The most common large vertebrate fossils found here are from 3-toed horses and rhinos both of which dominate Miocene fossil assemblages. A common species of horse of this era was the 60-pound Archaeohippus blackbergi. Many of the specimens suggest high mortality caused by intraspecific fights between males who sported long canines. Thomas Farm is the only site where bones of an extinct camel known as Floridatriculus dolochiantereus have been found. Extinct species of pronghorns also left fossil evidence in the sinkhole. The top predator was White’s bear-dog (Amphicyon whitei). It was related to the common ancestor of bears and dogs, and it grew to the size of a grizzly bear.

This 60 pound 3-toed horse was a common species in early Miocene forests. 3-toed horses occupied an ecological niche filled by white-tailed deer today.
Bear-dogs were a top predator during the early Miocene. White’s bear-dog grew to the size of a grizzly. They were related to the common ancestors of bears and dogs.
Extinct species of pronghorns ranged throughout southeastern North America during the Miocene. Today, there is just 1 species restricted to short grass prairies in some western states.

Farmers plowing a peanut field discovered Miocene-aged fossils at the Tyner Farm site. This site was excavated between 2001-2005, and fossils from this site are estimated to be 7.5 million years old. Paleontologists list 4 species of amphibians, 6 species of reptiles including 2 kinds of giant tortoise and the remains of the modern species of alligator (A. mississippiensis), and 25 species of mammals. The site yields the oldest dated fossil remains of a tree squirrel in North America. Like the older dated Thomas Farm site, the fossil assemblage is dominated by 3-toed horses and rhinos, though they are different species than those found at the older site. Bones of 4 species of horse, 2 species of rhino, 2 species of pronghorn, 3 species of camels, 1 species of tapir, and 1 species of peccary were found here. 1 species of camel is particularly remarkable–Aepycamelos major. It was 13 feet tall, not counting its 6-foot-long neck, and it weighed over a ton. This species is a good example of convergent evolution. Like giraffes, it evolved great height and a long neck to feed upon leaves and twigs other vertebrate herbivores couldn’t reach, and scientists refer to them as giraffe-camels. Top predators included the Borophagine or bone-eating dogs, and the saber-toothed cat (Machaerodes catcopsis). The latter species was likely ancestral to the more famous late Pleistocene species of saber-tooth cats.

This is the hippo-like rhino. Along with 3-toed horses, rhinos were the most common large herbivores during the late Miocene. Rhinos became extinct in North America at the end of the Miocene when Ice Ages began.
The amazing giraffe-camels are a great example of convergent evolution. Despite not being closely related to giraffes, they evolved long necks to help them reach the leaves at the top of trees they could eat.

Pleistocene North America is often compared to modern day Africa in its faunal diversity. However, as I’ve noted in a previous blog entry (See: https://markgelbart.wordpress.com/2013/12/09/the-faunal-diversity-of-pleistocene-north-america-was-less-than-that-of-modern-day-africa/ ), modern Africa far exceeds Pleistocene North America in number of genera and species. Miocene North America makes a better comparison in diversity because a far greater number of animal species occurred on the continent during this era. Ice Ages began occurring at the beginning of the Pliocene about 5 million years ago. Seasonal climates including sub-freezing weather severely reduced the number of species that could live in North America.



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