INTRODUCTION

Three salamander families are reported from the Mio-Pliocene Gray Fossil Site (GFS), Washington County, Tennessee (Figure 1): Ambystomatidae, Plethodontidae, and Salamandridae. Ambystomatidae have perhaps the best fossil record in the Mio-Pliocene of the three families present at the GFS, with vertebrae of Ambystoma cf. A. minshalli from the Coffee Ranch Local Fauna of Texas (Parmley 1989) and A. kansense, a neotenic form, from Edson Quarry, Kansas (Holman 2006). The Mio-Pliocene fossil record of the Plethodontidae is nearly exclusive to California with tracks and vertebrae from Batrachoseps found in the Pinhole Tuff, Mehrten Formation (Clark 1985; Holman 2006) and an otic bone of Aneides lugubris from Turlock Site 5 (Clark 1985). Up to this point only two Mio-Pliocene records of the family have been reported east of the Rockies, a single 'Plethodon-like' trunk vertebra from Coffee Ranch, Texas (Parmley 1989) and indeterminate plethodontid material from the Pipe Creek Sinkhole of Indiana (Farlow et al. 2001). The family Salamandridae has no skeletal fossil record in the Mio-Pliocene of North America, but is represented by a trackway in Kansas referred to Taricha sp. (Holman 2006).

GFS is the only Mio-Pliocene fossil site in the Appalachian region, providing a unique look at a diverse salamander assemblage in an upland environment. The fossil site covers roughly 1.8-2.0 ha, and fossiliferous sediments are as thick as 39 m (Wallace and Wang 2004; Nave et al. 2005). The site is composed of finely laminated clays, silts, and fine sands intermixed with isolated gravel lenses as the result of a small lake or pond filling a paleosinkhole within the Cambrian/Ordovician Knox Group Dolostone (Wallace and Wang 2004; Shunk et al. 2006; DeSantis and Wallace 2008; Hulbert et al. 2009). Weathering and erosion of the bedrock subsequent to the infilling has generated a reversed topography, leaving the fossil site as a high point (Wallace and Wang 2004; Shunk et al. 2006). The date of the GFS is inferred to be about 4.5 – 7 m.y.a. based on the co-occurrence of the rhinoceros Teleoceras and the tremarctine bear Plionarctos (Wallace and Wang 2004). The bulk of the herpetofauna (including alligators, natricine snakes, aquatic testudines, anurans, and salamanders) reflect a 'pond' environment (Schubert 2006; Schubert and Wallace 2006). As noted by Wallace and Wang (2004), Jiang and Liu (2008), and Liu and Jacques (2010), abundant plant macrofossils from Quercus (Oak) and Carya (Hickory), in the form of leaves, acorns and nuts, and isotope work by DeSantis and Wallace (2008) indicate a forest surrounded the 'pond'.

Fossils from the GFS provide a unique opportunity to examine a Mio-Pliocene sinkhole deposit in the southern Appalachians and add to the extent of the fossil record for salamanders in southeastern North America. The primary objectives of this report are to 1) identify salamander fossils from the GFS to family, subfamily or type, and genus by comparing them with skeletons of modern species from all extant families and published characters, 2) draw paleoecological inferences about the GFS (beyond those of Schubert 2006, and Schubert and Wallace 2006) based on physiological parameters and habitat preference of modern analogs through phylogenetic bracketing, and 3) further elucidate the evolutionary and biogeographic history of salamander clades in eastern North America. This paper represents a revised version of Boardman (2009).