FUNCTIONAL MORPHOLOGY AND DISTRIBUTION OF DALAMITIES. LIMULURUS GREEN IN MIDDLE TENNESSEE

The trilobite species Dalmanites lumulurus (Green) is abundant in the Upper Silurian Brownsport Fm and Lower Devonian Ross Fm of Central Tennessee. Numerous specimens of this species have been collected from locations in Decatur and Henry Counties TN. These specimens while not complete exhibit sufficient features to allow for inferences to be made about the life habit of this species. These characteristics include the visual range based on eye morphology, the overall morphology of the cephalon and pygidial regions and the presence of epibionts on several specimens. Three dimensional scans of nearly complete cephalons indicate D. limulurus had a visual range approaching 360 degrees in the horizontal plane. The smooth cephalon and relatively smooth pygida imply a type of stream lined morphology consistent with movement in a partial infaunal mode. Finally the presence of epibionts, on 3 specimens, all located on the dorsal surface of the cephalon and pygida indicate these regions where exposed at least postmortem. All of these features suggest a semi-infaunal live habit with the individuals maintaining only the highest portions of the body above the sediment water interface. This interpretation is re-enforced by the distribution of D. limulurus, which is most abundant in the shale facies of the Lobelville LS, member of the Brownsport and the Birdsong shale member of the Decatur Fm.