| |||||||
|
Thomas Farm
|
The 18 million-year-old, early Miocene Thomas Farm site is one of the richest terrestrial deposits of vertebrates in eastern North America. Tens of thousands of fossilized remains of both large and small vertebrates, an occurrence rarely encountered by paleontologists, have been uncovered. After nearly 70 years of collecting at Thomas Farm, it has become one of the most well known and documented Miocene vertebrate localities in North America. Yet, despite these seven decades of excavation in this small, almost circular depression (about 250 feet in diameter), Thomas Farm continues to amaze the paleontological community with its offerings.
The Discovery of Thomas Farm
Thomas Farm was first discovered in 1931 by Clarence Simpson, a staff member of the Florida Geological Survey (FGS), while he was investigating rumors that a Native American gravesite had been found among the sand hills of Gilchrist County in north central Florida. He had learned that a tenant farmer's plow had uncovered some bones in a shallow depression on the land of Raeford Thomas. While at the site C. Simpson collected specimens exposed on a spoil pile from a well and from a test pit he excavated nearby. After identifying some of the fossils as elements of an extinct three-toed horse, he forwarded them to George Gaylord Simpson of the American Museum of Natural History in New York City. G. Simpson immediately recognized the importance of the material. Not only did these specimens represent land mammals, they were also early Miocene in age, a combination at the time not commonly encountered in the eastern United States. The first scientific contributions on the Thomas Farm site appeared in 1932, when G. Simpson and A. E. Wood each described portions of the fauna.
Since most other sites of similar age in the eastern United States are of marine origin, the coincidental discovery of this fascinating snapshot into Florida's past quickly became regarded as one of the most important locality for Miocene terrestrial mammals east of the Rocky Mountains. Numerous paleontology luminaries of the time flocked to Thomas Farm over the next few decades. Thomas Barbour, the Director of the Museum of Comparative Zoology at Harvard University, examined some material stored in the FGS collections, and was so impressed with the potential of the site that in 1938 he purchased the surrounding 40-acre tract of land. In 1942 the property was deeded to Archie Carr, Zoology Department, University of Florida, who later donated the site as a "Fossil Preserve' to the Florida State Board of Education. The site was cooperatively excavated by teams led by staff members of Harvard University (B. Patterson, A. S. Romer, and T. E. White),
|
the Florida Geological Survey (S. J. Olsen), and the University of Florida (Puri and Vernon) from 1940 to 1958. Further excavations led by W. Auffenberg and T. H. Patton continued sporadically from the mid-1960's to the early 1970's. In late 1981, A. E. Pratt began her pivotal investigations into the taphonomy (mode of deposition and fossilization) of the large vertebrate fossil remains. In the early 1980's, members of the Society of Vertebrate Paleontology (1980) and the Florida Paleontological Society (1980 - 1983) visited Thomas Farm while participating in fieldtrips and annual workshops. Under the direction of B. MacFadden, Florida Museum of Natural History, the Pony Express program has been conducting annual weekend workshops at the site since the spring of 1992.
The Geological Setting of Thomas Farm
The sheer number of specimens, including both large and small vertebrates, prompts the question, "How did so many animal remains become entombed in such a small area at Thomas Farm?" Research over the past 70 years has emphasized two theories: 1. The site represents an ancient sinkhole. 2. The fossils were deposited at the site by a fluctuating stream. Although the actual depositional history of the site may never be known, A. Pratt, formerly of the University of Florida, presents a compelling argument in support of the sinkhole scenario. Paleontologists now generally agree that the Thomas Farm site is actually an ancient sinkhole, probably with an associated cave or caves, formed by dissolution of the underlying Eocene and Oligocene limestones. Herding and solitary large vertebrates fell into this death trap or were unable to climb out of it after they entered, perhaps in search of water. This sinkhole/cave theory is further supported by the presence of great numbers of fossilized bats, colonial mammals often inhabiting caves. Animal remains were rapidly covered with sediments and over the subsequent 18 million years became fossilized. The sinkhole and caves were later filled with surface sediments, and there one of the richest fossil localities in North America lay until uncovered in 1931.
Thomas Farm 18 Million Years Ago
|
Thomas Farm reveals a fossil land vertebrate fauna virtually unparalleled in diversity for its age, replete with amphibians, reptiles, birds, small rodents, bats, rhinoceroses, three species of three-toed horses, several artiodactyls (including camels, peccary, deer-like species and other extinct forms), as well as dogs, bears, and bear-dogs.
What can we learn from old bones? Through comparison with living species of the same or similar groups, this diverse array of fossil terrestrial vertebrates allows for a fairly detailed sketch of the local climate and habitats available in the Thomas Farm area 18 million years ago. Species related to some of the frogs and lizards found as fossils at Thomas Farm occur in tropical settings, an environment which no longer is present in north central Florida. The presence of these animals in the deposits strongly suggests a warmer climate in north central Florida during the early Miocene. Aquatic vertebrates, such as freshwater turtles, alligators, frogs, and particularly fish are relatively uncommon and often restricted to certain layers in the excavations, leading scientists to believe that Thomas Farm represents a pond which periodically went dry. Within the sinkhole and cave system lived the bats, probably some rodents, and their predators, such as boas and constricting snakes. The terrestrial environment around the Thomas Farm sinkhole was wooded, perhaps a mosaic of dense stands and forested savanna. Large birds similar to the kite of today flew overhead and smaller bird species sought food and safety from predators in the canopy, while arboreal squirrels scampered up and down the tree trunks. Turkeys foraged and rhinos and camel-like creatures browsed among the vegetation. On the trail to a watering hole, small herds of horses, particularly Parahippus leonensis, meandered in and out of the shaded forests wary of an attack by the voracious bear-dog, Amphicyon longiramus, or an ambush by the short-legged dog-like, Tomarctus canavus.
In short, although the climate is a little cooler and the composition of the larger vertebrate fauna is much different, the setting 18 million years ago was much like it is today in many parts of the state. Forested sinkholes abound in Florida. Still today these shady refuges, often supplied with ready access to water, attract animals because they offer food, shelter, and protection from predators. The Thomas Farm sinkhole provided all that and more. Eighteen million years and a farmer's plow later Thomas Farm offered paleontologists an exceedingly rare glimpse into the rich and varied life of the early Miocene of Florida.
Bibliography
Auffenberg, W. 1963. Present problems about the past. Biological Sciences Curriculum Study, Pamphlet no. 6:1-35.
Bader, R. S. 1956. A quantitative study of the Thomas Farm Miocene. Bulletin of the Museum of Comparative Zoology, Harvard University, 115:49-76.
Brodkorb, P. 1963. Miocene birds from the Hawthorne Formation. Quarterly Journal of the Florida Academy of Science, 26(2):159-167.
Holman, J. A. 1965. Early Miocene Anurans from Florida. Quarterly Journal of the Florida Academy of Science, 30(2):121-140.
Olsen, S. J. 1956. The Caninae of the Thomas Farm Miocene. Bulletin of the Museum of Comparative Zoology, Harvard University, 66:1-11.
Pratt, A. E. 1990. Taphonomy of the large vertebrate fauna from the Thomas Farm locality (Miocene, Hemingfordian), Gilchrist County, Florida. Bulletin of the Florida Museum of Natural History, 35(2):35-130.
Romer, A. S. 1948. The fossil mammals of Thomas Farm, Gilchrist County, Florida. Quarterly Journal of the Florida Academy of Science, 10:1-11.
Simpson, G. G. 1932. Miocene land mammals from Florida. Florida Geological Survey Bulletin, 10:7-41.
Webb, S. D. 1981. The Thomas Farm fossil vertebrate site. Florida Paleontological Society, Plaster Jacket, 37:6-25.
Wood, A. E. 1932. New heteromyid rodents from the Miocene of Florida. Florida Geological Survey Bulletin, 10:45-51.
Wood, H. E. 1964. Rhinoceroses from the Thomas Farm Miocene of Florida. Bulletin of the Museum of Comparative Zoology, Harvard University, 130:363-385.
Links
Florida Museum of Natural History, Vertebrate Paleontology http://www.flmnh.ufl.edu/vertpaleo/
Florida Paleontological Society - http://www.flmnh.ufl.edu/orgs/club.htm
Pony Express - http://www.flmnh.ufl.edu/ponyexpress/
Society of Vertebrate Paleontology - http://www.vertpaleo.org