PARALLELISM OF EUBRONTES TRACKWAYS IN THE HARTFORD BASIN: A COMPARISON ACROSS PALEOENVIRONMENTS

Parallel trackways of large theropods (Eubrontes giganteus) found in lacustrine sediments of the Lower Jurassic Portland Formation at Dinosaur Footprint Reservation in Holyoke, Massachusetts have been taken as evidence that these track makers were gregarious (Hitchcock 1848; Ostrom 1972). However, reexamination of the site by Getty et al. (2011) showed that the trackways trended approximately parallel to the crests of oscillation ripple marks, and that the trend continued throughout 100+ meters of strata at the site. Consequently, the parallel trackways were reinterpreted to indicate shoreline-paralleling behavior in the vicinity of a perennial lake. To test the generality of this behavior, Eubrontes orientations were examined at additional sites representing several paleoenvironments from the underlying East Berlin Formation of Connecticut and Massachusetts. The twelve Eubrontes trackways from playa facies rocks of the Murray Quarry (Getty 2005) are randomly oriented. Four beds at Powder Hill Dinosaur Park, representing fluvial/marginal lacustrine facies preserve tracks, but only one shows possible evidence of weakly preferred trackway orientation. No parallel trackways were reported from the lacustrine rocks of Dinosaur State Park (Ostrom 1972; Farlow and Galton 2003). Thus, trackway parallelism occurs in lacustrine facies, but the phenomenon is not ubiquitous in this environment. Considering that desiccation cracks and other evidence of subaerial exposure are rare at Dinosaur Footprint Reservation and more common elsewhere, we argue that the large numbers of parallel trackways there result from a stable shoreline, whereas the random orientations seen elsewhere result from greater freedom of motion around drying lakes. The evidence presented here does not support the hypothesis that the Eubrontes track maker was gregarious.