The ancient habitat of the Gray Fossil Site was apond formed within asinkhole surrounded by a warm, wet forest. The fossils found at the site represent the ancient plants and animals that lived and died in and around the sinkhole pond.
As the first site of its age known from theAppalachian region, the Gray Fossil Site is a unique window into the past. Research at the site has yielded many surprising discoveries, including new species ofred panda,rhinoceros,pond turtle,hickory tree, and more. The site also hosts the world's largest known assemblage of fossiltapirs.
In the area, now known as Tennessee, the world is known to have been much warmer, and with a climate that supported dense, humid forests.[5]
The Gray Fossil Site is a deposit of laminated clay and silt sediments laid down in an ancient lake that formed within a sinkhole. The deposit is oval in shape, covering an area of roughly 220 meters by 180 meters and ranging in depth from about 7 meters to 39 meters deep. The fossils within this deposit are abundant and often exceptionally well-preserved.[6]
Stratigraphic ranges of mammals from the Gray Fossil Site. All of these species overlapped between 4.5 and 4.9 million years ago (gray bar). Image from Samuels et al 2018.
The site is situated within theKnox Group formation, a series ofCambrian-Ordovicianlimestones. Groundwater flowing through joints in these rocks creates caves and sinkholes, forming a region ofkarst topography. The sinkhole that contains the fossil-rich deposits of the Gray Fossil Site is the result of a series of overlapping collapse events that ultimately formed one large basin. Sizable boulders deposited within the lake sediments indicate that the edge of the sinkhole once featured high walls or overhangs where chunks of rock could occasionally break off.[6]
Based on the assemblage of mammal fossils uncovered at the site, the main deposit is estimated to date between 4.5 and 4.9 million years old, during the EarlyPliocene Epoch near the transition of theHemphilian and Blancan Land Mammal Ages.[7] There is some evidence from drill cores for more ancient deposits deeper within the site, resulting from earlier stages of sinkhole collapse.[6]
Gray Fossil Site & Museum during the Grand Opening in 2007.
In late May 2000, this fossil-rich deposit was discovered during aTennessee Department of Transportation road construction project on the outskirts of Gray, TN. As it became clear that the fossils were unusual for this part of the country, members of the local community began an effort to preserve the site. In September 2000, Tennessee GovernorDon Sundquist announced that the construction project would be moved so the fossil site could be saved and dedicated to research and education.[8]
The Gray Fossil Site then became a project of East Tennessee State University, which began hiring paleontologists and geologists to oversee the site and ultimately to create a new Department of Geosciences. The university founded the Don SundquistCenter of Excellence in Paleontology and began construction of an on-site museum to house research facilities and educational exhibits. The museum first opened in August 2007, originally known as the East Tennessee State University and General Shale Brick Natural History Museum and Visitor Center, but now known more simply as theGray Fossil Site & Museum.[8]
The Gray Fossil Site was once a lake or pond surrounded by forest. The ancient lake was home to a diverse community of aquatic animals, including fish, pond turtles, aquatic salamanders, beavers, and alligators.[7] Plant fossils found at the site, particularlypollen, indicate that the dominant vegetation of the forest was oak, hickory, and pine trees, along with variousherbaceous species.[9] Estimates for the density of this forest have varied; earlier research suggested a moderately dense forest, while later study indicated that the site might have been more of an open woodland where disruptive factors such as large herbivores, frequent fire, and drought limited the development of a closedcanopy.[10]
A 2020 study used fossil mammal teeth as a proxy to estimate the ancient climate conditions of the Gray Fossil Site, estimating a mean annual temperature of 16.8 °C, or 62.2 °F (similar to modern-dayAtlanta, GA), and an annual precipitation of 1,343mm, or 52.9in (similar to modern-dayTampa, FL), with the minimum temperature of the coldest month reaching 2.6 °C, or 36.7 °F.[11] These results line up with earlier hypotheses that the site had a warmer and wetter climate than modern East Tennessee based on the presence of warm-climate animals and plants likealligators,tupelo, andCorylopsis.[10]
Many of the fossil fauna and flora of the Gray Fossil Site are closely related to modern-day species in Europe and Asia, including red pandas, European badgers, Chinese moonseed, andCorylopsis. This indicates that during the Early Pliocene, eastern North America maintained a biogeographic link withEurasia.[12][13]
The Gray Fossil Site is aLagerstätte that boasts a rich assemblage of well-preserved fossils. It is the only fossil site in the Appalachian region dating near the boundary between the Miocene and Pliocene Epochs, and therefore offers a unique window into this region at this time.[14]
In a research paper published in February 2025, researchers confirmed their finding of an ancient fossil for a cat-sized flying squirrel at the fossil site.[15] The animal,Miopetaurista webbi, was determined to have lived more than 4.75 million years ago and is believed to have swooped through the skies of Southern Appalachia.[16]
Salamanders. Several taxa have been identified, includingAmbystoma, Desmognathus, Notophthalmus, andPlethodon. These are the oldest known members of their families in the Appalachian mountains, a region well-known for its modern salamander diversity.[18]
Alligators. Several well-preserved specimens have been identified as the genusAlligator, but these appear to be distinct from known alligator species.[19]
Snakes. The most common snakes arecolubrids, of which several species have been identified, including the endemic fossil speciesZilantophis schuberti.Viperids are also present.[14]
Turtles. These are the most diverse group of reptiles at the site, including several taxa ofbox turtles,painted turtles,slider turtles,snapping turtles, andtortoises.[20] Among these are two species only known from the Gray Site: the musk turtleSternotherus palaeodorus[13] and the slider turtleTrachemys haugrudi.[20]T. haugrudi was named after Shawn Haugrud, the site's lab and field manager and lead preparator.[21]
Tapirus polkensis (dwarftapir). The Gray Fossil Site has the largest tapir population of any known fossil site, including fossil tapirs of all ages, from very young juveniles to old adults.[23]
Teleoceras aepysoma (rhinoceros). Several specimens are known, including two nearly complete skeletons. In 2019, the Gray Fossil Site rhinos were identified as a new species, named the "high-bodied"Teleoceras for their longer front legs compared to other species.[24][25]
Pristinailurus bristoli (red panda). Named as a new species in 2004. Two nearly complete skeletons make this one of the best-known fossil pandas in the world.[28]
Arctomeles dimolodontus (Eurasianbadger). This species was named alongside the Gray Fossil Site panda in 2004.[29]
Gulo sudorus (wolverine). The oldest known fossil wolverine. Named the "sweaty wolverine" since the ancient climate of Gray was much warmer than modern wolverine habitats.[7]
Mastodon. Likely a new species, represented by several specimens, including one nearly complete and very large skeleton. Early findings of proboscidean fossils at Gray were originally believed to belong to agomphothere.[31]
Aquatic invertebrates of the Gray Fossil Site includeostracods,snails, and smallclams.[34] Insects are also known from fossilized exoskeletal remains and trace fossils, including at least four different families ofbeetles.[35]
Plant fossils at the Gray Fossil Site include pollen, leaves, wood, fruits, seeds, and other structures which represent a diverse flora ofangiosperms,conifers,ferns,lycophytes, andbryophytes.[12][36] The forest flora was dominated by a variety of trees and shrubs, of which the most common werehickory,oak, andpine.[12][10]
Several previously unknown extinct plant species have been identified at the Gray Fossil Site:[12][10]
Algal microfossils have been identified as numerous freshwater species, including one previously unknown extinct species,Stigmozygodites grayensis, named after the Gray Fossil Site in 2013.[36]
^abcWhitelaw, Michael J.; Shunk, Aaron; Liutkus, Cynthia M. (2011). "Formation, Structure, and Fill of the Gray Fossil Site Basin".Schubert BS, Mead JI, Eds. Gray Fossil Site. 10 Years of Research:87–92.
^Schubert, Blaine W.; Mead, Jim I. (2011). "Alligators from the Gray Fossil Site".Schubert BS, Mead JI, Eds. Gray Fossil Site. 10 Years of Research:61–64.
^Steadman, David W. (2011). "A Preliminary Look at Fossil Birds from the Gray Fossil Site, Tennessee".Schubert BS, Mead JI, Eds. Gray Fossil Site. 10 Years of Research: 73.
^abcdefSchubert, Blaine W (2011). "History of the Gray Fossil Site and the Don Sundquist Center of Excellence in Paleontology".Schubert BS, Mead JI, Eds. Gray Fossil Site. 10 Years of Research:1–6.
^Hermsen, Elizabeth (February 3, 2023). "Pliocene seeds of Passiflora subgenus Decaloba (Gray Fossil Site, Tennessee) and the impact of the fossil record on understanding the diversification and biogeography of Passiflora".American Journal of Botany.110 (3).doi:10.1002/ajb2.16137.
^Hermsen, Elizabeth (May 18, 2021). "Review of the Fossil Record of Passiflora, with a Description of New Seeds from the Pliocene Gray Fossil Site, Tennessee, USA".International Journal of Plant Sciences.182 (6):533–550.doi:10.1086/714282.
