Florida: Horse Fossil Capital of the World
Lesson Created by: Jan Cubbage
Kentucky and Florida have had an argument the last few years as to which region is the
true “Horse Capital of the World”. Both states have genuine merits for their claims. But if the
title the two states were laying claim to was “Horse -Fossil Capital of the World” Florida wins
by a landslide. Actually, Florida wins by a sinkhole, for ancient sinkholes often became the
graveyards of animals that lived in Florida millions of years ago. Many of those animals became extinct and most of what paleontologists have learned about them is from fossil finds
here in Florida. Paleontologists agree that Florida has the richest fossil record of vertebrate animals of the eastern United States.
The earliest forms of horses evolved only in North America. As far back in time as 50
million years ago, horses of the earliest evolutionary forms roamed the continent. Many horse
species existed in North America. They all became extinct at the end of the last Ice Age, about
10,000 years ago. Before their extinction in North America, horses had migrated off and on beginning ten million years ago across the northern land bridge into Eurasia. Spanish and English
explorers and colonists brought horses to America in the 16 th century and North America was
repopulated with horses.
Fifty million years ago, the North American continent was covered by vast tropical forests. Then rather suddenly, 38 million years ago, there was a huge shift in climate to dry and
cool. Grasslands became the predominant landscape form in North America. The proto-equines
(forerunners of modern horses) adopted with great success to ecological changes over time.
They developed large molars to grind up grass. And, with all of those huge predators like the
saber toothed tiger lurking about, the little horses grew bigger. Their legs became remarkably
longer for quick starts and fast flights. The horses of this, the Oligocene period (38 to 24 million years ago), had three -toed feet with pads which worked well on the soggy ground of a
swampy environment.
Contrary to what the diagram in your Biology text illustrates, “there was no straight line
evolution of the horse. There was no family tree, it was a big bush and only one little twig survived” explains paleontologist, Mike Vorhees. Therefore the fossil records of extinct horses exhibit many species of various sizes over the millennium.
© Florida Agriculture in the Classroom, Inc.
During the Miocene period (24 to 5 million years ago) horses adapted further to being a
predominantly grass grazing animal. The horse’s molars developed gradually into a perfect
grinding surface by replacing a flat molar surface with a surface that had a series of concentric
ridges. The crowns of teeth became elongated and horse teeth became “hypsodontic” (hipe-sodon-tic), meaning the teeth grew continually as the crowns wore down. Continual eating of
abrasive dirt and sand covered grass causes the wearing down of the molar teeth of grazing animals.
For added speed to escape their many predators, horses of the later Miocene began to
develop one big toe, the toe in the middle of their three-toed foot. The foot pads and short stubby claws gradually disappeared because horses now had to run on hard, dry ground. Eventually, the middle toe was covered in a “horn” and it was very hard, and you might call it “hooflike”.
During the Pleistocene period, 1.6 million years ago to 10,000 years ago, the northern
regions of North America took on a big chill. Huge glaciers formed and melted and reformed
again in cycle fashion over a time period of one and a half million years. During this time,
horses grew much larger and the two side- toes of their feet became vestigal, meaning the two
side toes were still evident but had shrunk in size and were no longer a functional part of the
horse’s foot. At that time, horses had developed a true hoof. They had developed into one of
the fastest mammals on earth and had good foot traction on packed snow, ice or dirt.
There are many splendid fossil beds located in Florida. Most were located by accident.
If you want to find horse fossils in your neighborhood how would you go about it? Why not
build a race track for horses. By coincidence, this is exactly what Moss Bluff Farm near Morriston, Marion County did in December of 1984. The John Shimfessel family was developing
their new farm into a training center complete with a five-eighths mile race track. As excavation began to build the training track, many fossilized bones were churned up out of the clay as
a road-grader machine scraped away at a hill to level it for the far turn of the track.
Mr. Shimfessel had a good idea the hill that the big road scraper had dug into was a
treasure trove of ancient fossilized bones. The University of Florida paleontology department
was called in for a survey. The UF paleontologists were astounded by the amount of articulated
(bones connected together) mammal fossils that they found in just one day of digging and recovering at the site.
The site was identified by UF paleontologist, Gary Morgan, as a Late –Miocene, 10 to 5
million years ago fossil bed site. The location is known in formal reports as the “Moss Acres
Race Track Site”. A total of 480 specimens were recovered over a period of two years of work
and sent to the Florida Museum of Natural History for study. A number of the horse related
fossils are on display at the museum.
© Florida Agriculture in the Classroom, Inc.
The two most common species found at the Moss Acres site were of ancient rhino and a
small three-toed species of horse belonging to “genus Nannippus”. A previously undiscovered,
species of “shovel -tusk gomphothere” was the most remarkable discovery of the site. This
huge, odd beast was a relative of the mastodon.
Ancient horse species fossil recovered at the Moss Acres Site was the forelimb of the
one-toed horse called Dinohippus, the oldest evidence of one –toed horses in eastern North
America. Three species of tri-dactyl equids (three toed horses) were also recovered at the site.
The greenish- gray clay of the site was indicative of sediments found at the muck bottoms of ancient sinkholes. Very thirsty animals tend to crowd each other at watering holes. The
sides of the sinkhole-pond may have been steep and slippery resulting in falls into deep water.
After falling into the sinkhole pond, animals struggled to climb out but failed. Their bodies fell
to the bottom of the sinkhole to be covered over time with muck which then transformed into
dense clay over millions of years.
© Florida Agriculture in the Classroom, Inc.