In May of 2000, Tennessee Department of Transportation (TDOT) crews working on a road-widening project near the town of Gray in eastern Tennessee discovered an unusually dark, clay-rich deposit containing abundant fossils. This site became known as the Gray Fossil Site (GFS). Geologic interpretation of the GFS indicates that the deposit formed within a sinkhole that initially may have acted as a natural trap, then subsequently as a watering hole or pond1–4. Core samples show that the fossil-rich sediments cover roughly 4-5 acres and are up to 35-45 meters thick. The highly laminated, organic-laden, silty sediments are rich in both plant and animal remains. Based on the stratigraphic occurrence of GFS mammals, the age of the sediments is restricted to the early Pliocene Epoch between 4.5 and 4.9 million years ago5. Due to a paucity of similar-aged deposits within the Appalachians (and east-central North America in general), this site offers a significant opportunity to fill biogeographic and chronological gaps in the North American fossil record.
The GFS continues to produce extraordinary discoveries. Ongoing excavations every year and intensive screening and picking of excavated sediments have increased the taxonomic list to over 100 vertebrate taxa, including many new forms. Tapirus polkensis is the most abundant mammalian taxon (>100 individuals), including an unprecedented sample of many articulated skeletons representing all stages of ontogeny, as well as many skulls and jaws that are preserved in three dimensions1. Teleoceras aeypsoma (high-bodied rhino), a new species of rhino is represented by two nearly complete male skeletons and remains from at least three other individuals2. A new species of wolverine, Gulo sudorus3, is the oldest fossil representative of the genus. One of the signature animals at the GFS is Bristol’s Appalachian Panda (Pristinailurus bristoli), a new genus and species represented by two nearly complete skeletons which exhibit extreme sexual dimorphism; the large morph is nearly three times the size of the extant red panda, Ailurus fulgens4. Two beavers, Dipoides sp. and Castor sp. have been recovered from the site and likely occupied distinct dietary niches, implying that the former may have not exhibited behaviors similar to extant beavers.The GFS also contains an abundance of turtles, particularly semi-aquatic taxa, including two new species, Trachemys haugrudi and Sternotherus palaeodorus5,6. Other recent additions to the biota include: ostracods, gastropods, bivalves, insects (including several beetle families), lizards (including Heloderma10 sp.), snakes (including the new taxon Zilantophis schuberti11), rabbits, rodents, moles, peccaries7, and birds.
With the exquisite preservation of plants (> 30 genera), vertebrates, insects, and other invertebrates, the Gray Fossil Site not only preserves a unique forest ecosystem during a time of spreading grasslands across much of the continent, but should also be considered a true Lagerstätten.
Ongoing Research at the Gray Fossil Site
- Preparation and analysis of the GFS mastodon, with implications for mammutid evolution in North America
- Analysis of the early North American short-faced bear, Plionarctos
- Analysis of the GFS alligators
- Stable isotope perspectives on the paleoecology and climate of the GFS
- Bio-chronology and cosmogenic age dating of the GFS deposits
- Description of additional mammals from the site, including beavers, squirrels, mice, and woodrats, and camels
- Analysis of mammal community structure, comparing the body size, diet, and locomotion of species at the site to well-known late Miocene and Pliocene fossil sites across North America
References Cited (see link above for comprehensive bibliography)
1. Shunk, A. J., Driese, S. G. & Clark, G. M. Latest Miocene to earliest Pliocene sedimentation and climate record derived from paleosinkhole fill deposits, Gray Fossil Site, northeastern Tennessee, U.S.A. Palaeogeography, Palaeoclimatology, Palaeoecology 231, 265–278 (2006).
2. Shunk, A. J., Driese, S. G. & Dunbar, J. A. Late tertiary paleoclimatic interpretation from lacustrine rhythmites in the Gray Fossil Site, northeastern Tennessee, USA. Journal of Paleolimnology 42, 11–24 (2009).
3. Wallace, S. C. & Wang, X. Two new carnivores from an unusual late Tertiary forest biota in eastern North America. Nature 431, 556–559 (2004).
4. Whitelaw, J. L., Mickus, K., Whitelaw, M. J. & Nave, J. High-resolution gravity study of the Gray Fossil Site. GEOPHYSICS 73, B25–B32 (2008).
5. Samuels, J. X., Bredehoeft, K. E. & Wallace, S. C. A new species of Gulo from the Early Pliocene Gray Fossil Site (Eastern United States); rethinking the evolution of wolverines. PeerJ 6, e4648 (2018).
6. Hulbert, R. C., Wallace, S. C., Klippel, W. E. & Parmalee, P. W. Cranial morphology and systematics of an extraordinary sample of the Late Neogene dwarf tapir, Tapirus polkensis (Olsen). Journal of Paleontology 83, 238–262 (2009).
7. Short, R. A., Wallace, S. C. & Emmert, L. G. A New Species of Teleoceras (Mammalia, Rhinocertotidae) from the Late Hemphillian of Tennessee. Bulletin of the Florida Museum of Natural History 56, 183–260 (2019).
8. Fulwood, E. L. & Wallace, S. C. Dimorphism in Pristinailurus: evidence for unusual size dimorphism in a fossil ailurid. Palaeontologica Electronica 18, 1–6 (2015).
9. Bourque, J. R. & Schubert, B. W. Fossil musk turtles (Kinosternidae, Sternotherus) from the late Miocene-early Pliocene (Hemphillian) of Tennessee and Florida. Journal of Vertebrate Paleontology 35, 37–41 (2015).
10. Jasinski, S. E. 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 6, e4338 (2018).
11. Doughty, E. M., Wallace, S. C., Schubert, B. W. & Lyon, L. M. 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 6, e5926 (2018).