CONTRASTING BEHAVIORAL AND FEEDING STRATEGIES RECORDED BY TIDAL-FLAT BIVALVE TRACE FOSSILS FROM THE UPPER CARBONIFEROUS OF EASTERN KANSAS

Upper Carboniferous tidal-flat deposits near Waverly, eastern Kansas ( Stull Shale Member, Kanwaka Shale Formation), host abundant and very w ell-preserved trace fossils attributed to the activity of burrowing bi valves. Thin shell lenses with an abundant bivalve fauna are associate d with the ichnofossil-bearing beds and afford an unusual opportunity to relate trace fossils to their makers. Two distinctive life and feed ing strategies can be reconstructed on the basis of trace fossil analy sis and functional morphology. Lockeia siliquaria hyporeliefs commonly are connected with vertical to inclined, truncated endichnial shafts in the absence of horizontal locomotion traces. These structures recor d vertical and oblique displacement through the sediment, and suggest relatively stable domiciles rather than temporary resting traces as ty pically considered. Crowded bedding surfaces displaying cross-cutting relationships between, specimens of L, siliquaria and differential pre sentation at the top (concave versus convex epireliefs) record a compl ex history of successive events of colonization, erosion, deposition, and recolonization (time-averaged assemblages). Irregular contours of some large hypichnia indicate the cast of the foot, while other outlin es closely match the anterior area of Wilkingia, its suggested tracema ker. Relatively stable, vertical to inclined life positions and domina nt vertical mobility suggest a filter-feeding strategy. Moreover, the elongate shell and pallial sinus of Wilkingia provide a strong indepen dent line of evidence for an opisthosiphonate, moderately deep-tier in habitant. Wilkingia may represent a pioneer attempt at siphon-feeding in the Late Paleozoic, preceding the outcome of the Mesozoic infaunal radiation. A second strategy is represented by Lockeia ornata and asso ciated Locomotion, and locomotion/feeding structures. Lockeia ornata i s commonly connected with chevron locomotion traces that record the bi furcated foot of a protobranch bivalve. Lockeia ornata exhibits distin ctive, fine, parallel lines that mimic the ornamentation of Phestia, a nuculanid protobranch bivalve. Rosary and radial structures give evid ence of a patterned search for food. Lockeia ornata and associated Pro tovirgularia record dominant horizontal Locomotion and suggest the act ivity of deposit-feeding bivalves. Morphologic variability of Protovir gularia was controlled by substrate fluidity, which was dependent on s ediment heterogeneity and tidal-cycle dynamics. This study demonstrate s that detailed analysis of bivalve traces provides valuable informati on on bivalve ethology and paleoecology, evolutionary innovations, env ironmental dynamics, and substrate fluidity.