TRILOBITE FAUNA OF THE BROWNSPORT FORMATION (UPPER SILURIAN) WEST TENNESSEE

The Brownsport formation (Upper Silurian) of West Tennessee is a mixed limestone and shale unit generally interpreted as deposited on a storm dominated shelf. The Brownsport contains a diverse and generally well documented typical mid-Paleozoic fauna. One gap in the study of the fossil fauna of the Brownsport has been trilobites. Although several species have been documented in the Brownsport, no modern extensive collections have been reported and most published descriptions are based on collections developed in the early to mid 20^th century. This report documents the trilobite fauna of the Brownsport based on recent field collections. The fauna consists of at least nine species (Dalmanites limulurus, Calymene spp., Balizoma ramskoeldi, Mackenziurus spp., Paciphacops logani birdsongensis, Fragiscutum glebale, Greenops c.f. boothi, Crotalocephalus? spp. and two unidentified species. Of the above taxa, five (Friagiscutum glebale, Dalmanites limulurus, Balizoma ramskoeldi Mackenziurus spp., and Claymene spp.) have been previously reported from the Brownsport Fm. The presence of a tentatively identified Crotalochephalus? spp. marks a substantial increase in the geographic range of this taxa as it has not been previously reported from North America. Both Paciphacops logani birdsongensis and Greenops c.f. boothi have previously only been reported from Lower Devonian units. In addition, Greenops has never been reported from Tennessee. The presence of these two taxa may indicate an environmental control on the distribution. Both taxa were collected from the upper part of the Lobelville member, the most shale rich part of the Brownsport. P. logani birdsongensis has been previously reported mostly from the Birdsong shale (Lower Devonian) which is very similar in lithology to the Lobelville.