SWIMMING THEROPODS? A NEW INVESTIGATION OF UNUSUAL THEROPOD FOOTPRINTS FROM DINOSAUR STATE PARK, ROCKY HILL, CT (NEWARK SUPERGROUP, EASTERN NORTH AMERICA)

Dinosaur State Park (Rocky Hill, CT) is the site of a large track-bearing surface in the Hettangian East Berlin Formation (Newark Supergroup, Hartford Basin) dominated by the prints of theropod dinosaurs. The main track surface is a medium- to coarse-grained poorly sorted micaceous sandstone with subangular grains (mostly quartz); most of the silt- to coarse-sand sized mica is on the bedding planar surface. The East Berlin Formation is an example of one of the cyclical lacustrine units of the Hartford basin. Most of the theropod footprints are large (Eubrontes cf. giganteus) although smaller examples occur. Several prints are infilled by ripple-marked sandstone, with very little of the footprint morphology visible; therefore, it is likely that the main track-bearing surface is the surface these dinosaurs were walking on. Several trackways bear prints of unusual morphology, interpreted by Coombs (1980, Science v 207 p 1198) as tracks of swimming dinosaurs. These prints are tridactyl, consisting of three parallel grooves, the outer ones often 'pinching' in the middle while the central groove tends to be shorter and terminates posteriorly in a circular or semi-circular impression. Three parallel trackways each exhibit variation in preservation and morphology in the same direction on the track surface (regardless of the direction the trackmaker was walking in); trackways perpendicular to these show no variation in morphology. An isolated footprint is intermediate in morphology between the 'true' Eubrontes morphology and the 'swim-tracks', with both grooves and phalangeal pads present. One 'swim-track' is partially overprinted by a Eubrontes. We interpret these 'swim-tracks' as poorly-preserved footprints made on the main track-bearing surface prior to the main period of track-making (i.e, before the 'normal' Eubrontes prints); the grooves are simply poorly preserved digits, rather than claw drag-marks made by a dinosaur pushing off the lake-bed while swimming.