16 December 2015

16. Gray Fossil Site

Rhinos, alligators, and tapirs from the Gray Site
Phil Fraley Productions
Location: Tennessee, USA
Formation: Sediment fill in the Knox Group
Age: Miocene (7-5 Ma)

By the end of the Miocene, grasslands had expanded across the interiors of most continents, but that is not to say that forests went extinct.  In places where temperature and precipitation remained favorable, forests of various kinds continued to flourish even as global climate cooled and dried.  The Appalachians were one such area, and at the end of the Miocene they were blanketed in woods of oak, hickory, and pine similar in many ways to those of the southern end of the mountain range today.  East Tennessee sits atop carbonate rocks that can be dissolved by water, leading in places to the collapse of overlying sediments to form sinkholes.  One such sinkhole in eastern Tennessee that existed in the closing days of the Miocene accumulated the remains of plants and animals from the area that would eventually become one of the richest vertebrate fossil-bearing sites in eastern North America.  Because it represents a forest from an interval with a fossil record dominated by grasslands, the Gray Fossil Site has yielded many animals not commonly seen elsewhere.  Perhaps the most interesting of these are animals that migrated to North America from elsewhere as cooling temperatures, lowering sea levels, and the movement of tectonic plates facilitated the movement of species across the globe.  North America and Asia were connected many times over the course of the Cenozoic, and some Asian immigrants found at the Gray Site, such as elephant-like gomphotheres and cats (including some of the saber-toothed variety), had arrived on the continent in the mid-Miocene.  Others, such as bears and, bizarrely, red pandas, were much more recent arrivals.  Perhaps most significant of all, though, were giant ground sloths, the earliest and among the most successful of migrants from South America, which until the end of the Miocene had been comparable to Australia in its isolation from the rest of the world.  There are also plenty of North American natives at the Gray Site, the most common of which were tapirs (which, though they are extinct on the continent today, have a fossil record here dating back to the Eocene).  The dwarf species Tapirus polkensis has been found in such numbers, and in such good states of preservation, that it's been the focus of population ecology analyses, an area of study that usually cannot be applied to fossil vertebrates.

Visit: East Tennessee State University in Johnson City owns the Gray Site and operates a museum there.
Fossils: As opposed to many of the lagerstätten featured this month, fossils of which are often scattered through several collections, pretty much everything from the Gray Site has wound up in the ETSU collections.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: There is!

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

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