Gunn Farm Mine

University of Florida Vertebrate Fossil Locality GD006

Location

Gunn Farm Mine is located about 7 miles (11.2 km) north of Quincy, Gadsden County, Florida, to the east of Willacoochee Creek and just south of the Florida-Georgia state line. 30.70º N; 84.54º W.

Age

  • Middle Miocene Epoch; early Barstovian (Barstovian 1) land mammal age
  • 16-15 million years ago

Basis of Age

The Gunn Farm Mine vertebrate fossils are regarded as early Barstovian based on the co-occurrence of the small rodents Copemys sp. and Perognathus cf. P. minutus, and the hedgehog Lanthanotherium (Bryant, 1991). A numeric date of 15.6 million years before present was obtained from ratios of stable isotopes of strontium in a fossil mollusk shell collected in a bed above the terrestrial vertebrate fossil level (Bryant, 1990; MacFadden et al., 1991). This date has a wide error range of ± 1.4 million years, so is not very precise, but does confirm the middle Miocene, early Barstovian age.

Geology

The fossils from the Gunn Farm Mine derive from the Dogtown Member of the Torreya Formation, part of the Hawthorn Group (Bryant, 1991). According to Bryant (1990), marine vertebrate and invertebrate fossils were common throughout the beds belonging to the Dogtown Member in the Gunn Farm Mine, but that the terrestrial vertebrate fossils were limited to a single bed of sandstone with carbonate cement found only in the northern part of the mine.

Depositional Environment

Overall nearshore marine, with the bed producing the terrestrial fossils possibly a delta or some other fluvial channel.

Fossils

There are about 1,100 identifiable specimens from the Gunn Farm Mine housed in the Florida Museum of Natural History UF collection. The Gunn Farm Mine produced the best known example of an in situ terrestrial vertebrate assemblage belonging to the middle Miocene Willacoochee Fauna (Bryant, 1991). All specimens found are isolated; most commonly teeth and partial limb bones and vertebrae. No skulls or complete jaws were found. Small- to medium-sized shark and myliobatid ray teeth were the most abundant fossils. Small terrestrial vertebrates were recovered by screenwashing. Within the nonmarine component of the fauna, freshwater turtles and land tortoise are relatively common.

Complete Faunal Fossil List (Click to view)

Excavation History and Methods

The first collected fossils in the UF collection from Gunn Farm Mine were found on spoil piles and donated by geologist Muriel E. Hunter. Amateur collector Jim Morris took J. Danial Bryant, then of UF geology graduate student to the Gunn Farm Mine for the first time in September 1987. Bryant returned to this mine to collect fossils several times afterward, with the last trip in January 1989. About 800 kg (1760 pounds) of matrix was collected for screen-washing and hauled out of the mine in several trips in late 1988 and early 1989 (Bryant, 1990). In addition to screenwashing, fossils were recovered by prospecting outcrops and search spoil piles.

Discussion

The fossils from the Gunn Farm Mine were assigned to the Willacoochee Fauna by Bryant (1991). This assemblage is derived from fuller’s earth mines in northern Gadsden County and adjacent counties in southwest Georgia. While the larger vertebrates from the Gunn Farm Mine have also been found at other fuller’s earth mines in Gadsden County, it is the small species recovered by screenwashing that have the most scientific significance. The nearby La Camelia Mine also produced small rodent teeth, but in fewer numbers than Gunn Farm Mine. The record of Lanthanotherium (based on a single upper molar) is the only known occurrence of this extinct hedgehog in eastern North America. It is also known from Europe. Among the small rodents, heteromyids are still common, but so is the cricetid Copemys, which was a recent immigrant from Asia that became increasingly more common across North America during the mid- to late Miocene. The Gunn Farm Mine also produced the rare giant salamander Batrachosauroides dissimulans.

Sources

  • Author: Richard C. Hulbert Jr.
  • Completion Date: April 7, 2015
  • Editor(s) Name(s): Natali Valdes
  • Last Updated: June 16, 2015
Scientific References (Click to View)

 

This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. 

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