MATERIALS AND METHODS

Fossil Collection and Identification

Vertebrate microfossil remains were collected by water screening matrix from various test pits at the GFS using 1.7 mm mesh box screens. Screened residue was then picked under a dissecting microscope, and remains were sorted by class and order. Preliminary identification of the salamander fossils was done by comparison under a light microscope with modern specimens housed and/or on loan at East Tennessee State University. Though salamander cranial and postcranial materials are known from the GFS, they are exceedingly rare and difficult to identify below family level; so vertebrae are used exclusively for identification purposes in this study.

Identification of fossil salamander skeletal elements is complicated by the overall simplicity of salamander bones in general, phylogenetic/ontogenetic variation, and similarity between unrelated taxa. The inferred age of the GFS (about 4.5 – 7 m.y.a.), and lack of specific morphological characters, makes species attribution based on vertebrae seemingly implausible. For these reasons fossil taxa are identified to the level of genus where possible. Because vertebrae are the most numerous elements in the skeleton and the most represented fossil element for this group at the GFS, special attention was given to vertebral anatomy. Following the osteological scheme of Duellman and Trueb (1994), the salamander vertebral column consists of five differentiated regions: cervical (consisting of the atlas), trunk (containing a variable number of vertebrae from 10 to 60 depending on genus or species), sacrum (consisting of one sacral vertebra), caudosacral (consisting of two to four vertebrae), and caudal region (with a variable number of vertebrae from 20 to more than 100). GFS salamander vertebrae were identified by comparing the fossil material with modern specimens from all families and literature on various modern and fossil taxa. Comparative specimens used for this analysis were from the Carnegie Museum of Natural History (CMNH), University of California Museum of Vertebrate Zoology (UCMVZ), New Jersey State Museum (NJSM), Appalachian State University (ASU), and from the East Tennessee State University Vertebrate Paleontology Laboratory (ETVP).

After preliminary examination of both modern comparative and fossil specimens, and literature regarding vertebral characters of extinct families (e.g., the Batrachosauroididae), it was clear that none of the analyzed fossil specimens represented extinct families. Following this finding, two assumptions are posited in regards to identity of GFS specimens: 1) specimens represent extant families (i.e., no Batrachosauroididae), and 2) the presence of spinal nerve foramina posterior to the transverse processes in examined fossil trunk vertebrae limited identifications to members of the extant families Ambystomatidae, Plethodontidae, Salamandridae, and Sirenidae (as noted by Edwards 1976). Where identifications are made to gen. et sp. indet., further identification is discussed but left for future work due to a lack of confidence in generic level characters.

Data Analysis

Screening and sorting of fossil rich sediment at the GFS is an ongoing process so salamander vertebrae are continually recovered. Thus, the analysis here is based on a sample from the fossil site. Though this sample may not be entirely reflective of taxon abundance or diversity, it does give a preliminary view of the GFS salamander assemblage. Relative abundances of fossil salamander taxa are represented in two ways, 1) the number of identified elements for the taxon (NIE), and 2) minimum number of individuals for the taxon (MNI). MNI is a conservative estimate of the minimum number of individuals of a taxon that are necessary to account for the number of skeletal elements in the identified sample.

Systematic Accounts

A total of 181 pre-caudal vertebrae were identified and represent at least five salamander genera. Vertebral identification methods are emphasized here because vertebrae are the most abundant salamander elements from the site (and the only recovered elements identifiable beyond ordinal level). Each fossil genus account includes a breakdown of the identified vertebrae by position in the vertebral column, NIE, MNI, and remarks regarding the identification of these elements. Anatomical terminology follows that of Duellman and Trueb (1994), Miller (1992), and Holman (2006). Classification used was that of Duellman and Trueb (1994), Larson et al. (2006), and Chippindale et al. (2004).