Gray Fossil Site Explained

The Gray Fossil Site is an Early Pliocene assemblage of fossils dating between 4.5 and 4.9 million years old, located near the town of Gray in Washington County, Tennessee. The site was discovered during road construction on Tennessee State Route 75 by the Tennessee Department of Transportation in May 2000,^[1] after which local officials decided to preserve the site for research and education. The site became part of East Tennessee State University, and the Gray Fossil Site & Museum was opened on the site in 2007.

The ancient habitat of the Gray Fossil Site was a pond formed within a sinkhole 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 the Appalachian region, the Gray Fossil Site is a unique window into the past. Research at the site has yielded many surprising discoveries, including new species of red panda, rhinoceros, pond turtle, hickory tree, and more. The site also hosts the world's largest known assemblage of fossil tapirs.

Formation

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.^[2] The site is situated within the Knox Group formation, a series of Cambrian-Ordovician limestones. Groundwater flowing through joints in these rocks creates caves and sinkholes, forming a region of karst 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.

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 Early Pliocene Epoch near the transition of the Hemphilian and Blancan Land Mammal Ages. There is some evidence from drill cores for more ancient deposits deeper within the site, resulting from earlier stages of sinkhole collapse.

History

In late May 2000, this fossil-rich deposit was discovered during a Tennessee 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 Governor Don Sundquist announced that the construction project would be moved so the fossil site could be saved and dedicated to research and education.^[3]

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 Sundquist Center 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 the Gray Fossil Site & Museum.

Paleoenvironment

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. Plant fossils found at the site, particularly pollen, indicate that the dominant vegetation of the forest was oak, hickory, and pine trees, along with various herbaceous species.^[4] 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 closed canopy.

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-day Atlanta, GA), and an annual precipitation of 1,343mm, or 52.9in (similar to modern-day Tampa, FL), with the minimum temperature of the coldest month reaching 2.6 °C, or 36.7 °F.^[5] 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 like alligators, tupelo, and Corylopsis.

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, and Corylopsis. This indicates that during the Early Pliocene, eastern North America maintained a biogeographic link with Eurasia.

Fossils

The Gray Fossil Site is a Lagerstätte 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.

Fish

So far, all of the fish fossils identified at the Gray Fossil Site belong to the family Centrarchidae.^[6]

Amphibians

• Salamanders. Several taxa have been identified, including Ambystoma, Desmognathus, Notophthalmus, and Plethodon. These are the oldest known members of their families in the Appalachian mountains, a region well-known for its modern salamander diversity.^[7]
• Frogs. Numerous taxa, including Rana.

Reptiles

• Alligators. Several well-preserved specimens have been identified to the genus Alligator, but these appear to be distinct from known alligator species.^[8]
• Lizards. Identified lizards include skinks, anguids, and helodermatids.^[9]
• Snakes. The most common snakes are colubrids, of which several species have been identified, including the endemic fossil species Zilantophis schuberti. Viperids are also present.
• Turtles. These are the most diverse group of reptiles at the site, including several taxa of box turtles, painted turtles, slider turtles, snapping turtles, and tortoises. Among these are two species only known from the Gray Site, the musk turtle Sternotherus palaeodorus^[10] and the slider turtle Trachemys haugrudi.^[11] T. haugrudi was named after Shawn Haugrud, the site's lab and field manager and lead preparator.^[12]

Birds

A preliminary study in 2011 identified several families of birds at the Gray Fossil Site, the most common of which were ducks.^[13]

Mammals

Perissodactyls (odd-toed hoofed mammals)

• Tapirus polkensis (dwarf tapir). 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.^[14]
• 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.^{[15] [16]}
• Cormohipparion emslei (three-toed horse)^[17]

Artiodactyls (even-toed hoofed mammals)

• Peccaries. Two species have been identified: Mylohyus elmorei and Prosthennops serus.^[18]
• Pediomeryx.^[19]
• Camel, possibly Megatylopus.

Carnivora

• 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.^[20]
• Arctomeles dimolodontus (Eurasian badger). This species was named alongside the Gray Fossil Site panda in 2004.^[21]
• 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.^[19]
• Plionarctos (short-faced bear).
• Saber-toothed cat, possibly Machairodus.
• Buisnictis breviramus (skunk).
• Borophagus (bone crushing dog).^[22]

Proboscidea (elephants)

• 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 a gomphothere.^[23]

Rodents

• Several species, including beavers, packrats, and mice.

Lagomorphs

• Alilepus vagus (rabbit).
• Notolagus lepusculus (rabbit)^[24]

Bats

• Two species of vespertilionid bats.^[25]

Eulipotyphla

• Several species of shrews and moles.

Xenarthra

• An unknown species of megalonychid sloth.

Invertebrates

Aquatic invertebrates of the Gray Fossil Site include ostracods, snails, and small clams.^[26] Insects are also known from fossilized exoskeletal remains and trace fossils, including at least four different families of beetles.^[27]

Plants

Plant fossils at the Gray Fossil Site include pollen, leaves, wood, fruits, seeds, and other structures which represent a diverse flora of angiosperms, conifers, ferns, lycophytes, and bryophytes.^[28] The forest flora was dominated by a variety of trees and shrubs, of which the most common were hickory, oak, and pine.^{[29] [30]}

Several previously unknown extinct plant species have been identified at the Gray Fossil Site:

• Carya tennesseensis (hickory)
• Sinomenium macrocarpum (moonseed)
• Staphylea levisemia (bladdernut)
• Three species of Vitis (grapes)
• Corylopsis grisea (witch hazel)
• Cavilignum pratchettii, the first extinct genus of plant identified at the Gray Fossil Site.

Algae

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.

Fungi

Several types of fungi have been identified from microfossil remains of fungal tissue and fruiting bodies.^[31]

See also

• Ashfall Fossil Beds
• Pipe Creek Sinkhole
• La Brea Tar Pits
• Lagerstätte
• List of fossil sites (with link directory)

External links

• ETSU Gray Fossil Site & Museum website
• Research at the Gray Fossil Site
• ETSU Natural History Museum & Gray Fossil Site YouTube Channel
• The Paleobiology Database: Gray Fossil Site Taxonomic List
• Hands On! Discovery Center
• Friends of Gray Fossil Site
• Early photos and activities
• Tennessee State Web page

36.386°N -82.498°W

Notes and References

1. Book: The Gray Fossil Site: A Spectacular Example in Tennessee of Ancient Regolith Occurrences in Carbonate Terranes, Valley and Ridge Subprovince, Southern Appalachians U.S.A. . April 26, 2012 . . 10.1061/40796(177)10 . https://ascelibrary.org/doi/abs/10.1061/40796%28177%2910 . November 25, 2022. Sinkholes and the Engineering and Environmental Impacts of Karst . Clark . G. Michael . Kohl . Martin . Moore . Harry L. . Sasowsky . Ira D. . 82–90 . 978-0-7844-0796-7 .
2. Whitelaw. 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.
3. Web site: History ETSU Gray Fossil Site and Museum. 2021-01-21. www.etmnh.org.
4. Ochoa. Diana. Zavada. Michael S.. Liu. Yusheng. Farlow. James O.. 2016-06-01. Floristic implications of two contemporaneous inland upper Neogene sites in the eastern US: Pipe Creek Sinkhole, Indiana, and the Gray Fossil Site, Tennessee (USA). Palaeobiodiversity and Palaeoenvironments. en. 96. 2. 239–254. 10.1007/s12549-016-0233-4. 130605583. 1867-1608.
5. Schap. Julia A.. Samuels. Joshua X.. Joyner. T. Andrew. 2021-01-15. Ecometric estimation of present and past climate of North America using crown heights of rodents and lagomorphs. Palaeogeography, Palaeoclimatology, Palaeoecology. en. 562. 110144. 10.1016/j.palaeo.2020.110144. 2021PPP...562k0144S. 135298538. 0031-0182.
6. Woodward. Brett. 2011. Fishes of the Mio-Pliocene Gray Fossil Site. Schubert BS, Mead JI, Eds. Gray Fossil Site. 10 Years of Research. 93–95.
7. Boardman. Grant S.. Schubert. Blaine W.. 2011. First Mio-Pliocene salamander fossil assemblage from the southern Appalachians. Palaeontologia Electronica. 14.
8. 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.
9. Jasinski. Steven E.. Moscato. David A.. 2017-06-01. Late Hemphillian Colubrid Snakes (Serpentes, Colubridae) from the Gray Fossil Site of Northeastern Tennessee. Journal of Herpetology. en. 51. 2. 245–257. 10.1670/16-020. 90960539. 0022-1511.
10. Bourque. Jason R.. Schubert. Blaine W.. 2015-01-02. Fossil musk turtles (Kinosternidae, Sternotherus) from the late Miocene–early Pliocene (Hemphillian) of Tennessee and Florida. Journal of Vertebrate Paleontology. 35. 1. e885441. 10.1080/02724634.2014.885441. 86840420. 0272-4634.
11. Jasinski. Steven E.. 2018-02-13. A new slider turtle (Testudines: Emydidae: Deirochelyinae: Trachemys) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines. PeerJ. en. 6. e4338. 10.7717/peerj.4338. 29456887. 5815335. 2167-8359. free.
12. News: 5.5 million-year-old fossil turtle species sheds light on invasive modern relatives . 12 July 2022 . Penn Today . en.
13. 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.
14. Schap. Julia A.. Samuels. Joshua X.. 2020-05-26. Mesowear Analysis of the Tapirus polkensis population from the Gray Fossil Site, Tennessee, USA. Palaeontologia Electronica. English. 23. 2. 1–16. 10.26879/875. 1094-8074. free.
15. Short. Rachel. Emmert. Laura. 2019. A new species of Teleoceras (Mammalia, Rhinocerotidae) from the Late Hemphillian of Tennessee. Bulletin of the Florida Museum of Natural History. 56. 183–260. Florida Museum of Natural History.
16. Web site: A new species of rhino. 2021-01-19. www.etsu.edu.
17. Schubert. 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.
18. Doughty. Evan M.. Wallace. Steven C.. Schubert. Blaine W.. Lyon. Lauren M.. 2018-11-30. First occurrence of the enigmatic peccaries Mylohyus elmorei and Prosthennops serus from the Appalachians: latest Hemphillian to Early Blancan of Gray Fossil Site, Tennessee. PeerJ. en. 6. e5926. 10.7717/peerj.5926. 30533292. 6276594. 2167-8359. free.
19. Samuels. Joshua X.. Bredehoeft. Keila E.. Wallace. Steven C.. 2018-04-18. A new species of Gulo from the Early Pliocene Gray Fossil Site (Eastern United States); rethinking the evolution of wolverines. PeerJ. en. 6. e4648. 10.7717/peerj.4648. 29682423. 5910791. 2167-8359. free.
20. Fulwood. Ethan L.. Wallace. Steven C.. 2015-09-01. Evidence for unusual size dimorphism in a fossil ailurid. Palaeontologia Electronica. English. 18. 3. 1–6. 10.26879/526. 1094-8074. free.
21. Wallace. Steven C.. Wang. Xiaoming. September 2004. Two new carnivores from an unusual late Tertiary forest biota in eastern North America. Nature. en. 431. 7008. 556–559. 10.1038/nature02819. 15457257. 2004Natur.431..556W. 4432191. 1476-4687.
22. Bōgner . Emily . Samuels . Joshua X. . 2022-07-25 . The first canid from the Gray Fossil Site in Tennessee: new perspective on the distribution and ecology of Borophagus . Journal of Paleontology . 96 . 6 . 1379–1389 . 10.1017/jpa.2022.46 . 0022-3360. free .
23. Web site: Elephantine undertaking: Digging up a giant mastodon Fossils Earth Touch News. 2021-01-19. Earth Touch News Network. en.
24. Samuels . Joshua X . Schlap . Julia . Early Pliocene Leporids from the Gray Fossil Site of Tennessee . Eastern Paleontologist . 8 . 1–23 . ResearchGate.
25. Czaplewski. Nicholas J.. 2017-04-27. First report of bats (Mammalia: Chiroptera) from the Gray Fossil Site (late Miocene or early Pliocene), Tennessee, USA. PeerJ. en. 5. e3263. 10.7717/peerj.3263. 28462055. 5410148. 2167-8359. free.
26. Web site: Gray Fossil Site in Tennessee. 2021-01-16. www.tn.gov. en.
27. Doby. Joshua R.. Wallace. Steven C.. 2014. Fossil Insects of the Gray Fossil Site (Hemphillian) Washington County, Tennessee. The Paleontological Society Special Publications. en. 13. 86–87. 10.1017/S2475262200011850. 2475-2622.
28. Worobiec. Elzbieta. Liu. Yu-Sheng (Christopher). Zavada. Michael S.. 2013. Palaeoenvironment of Late Neogene lacustrine sediments at the Gray Fossil Site, Tennessee, USA. Annales Societatis Geologorum Poloniae. 83. 51–63.
29. Quirk. Zack J.. Hermsen. Elizabeth J.. Neogene Corylopsis seeds from eastern Tennessee. Journal of Systematics and Evolution. 2020. 59. 3. 611–621. en. 10.1111/jse.12571. 1759-6831. free.
30. Siegert. Caroline. Hermsen. Elizabeth J.. 2020-04-01. Cavilignum pratchettii gen. et sp. nov., a novel type of fossil endocarp with open locules from the Neogene Gray Fossil Site, Tennessee, USA. Review of Palaeobotany and Palynology. en. 275. 104174. 10.1016/j.revpalbo.2020.104174. 0034-6667. free.
31. Worobiec. Grzegorz. Worobiec. Elzbieta. Liu. Christopher (Yusheng). 2018. Fungal remains from late Neogene deposits at the Gray Fossil Site, Tennessee, USA. Mycosphere. 9. 5. 1014–1024. 10.5943/mycosphere/9/5/5. free.