DINOSAUR FOOTPRINTS AT THE NASH DINOLAND QUARRY (LOWER JURASSIC PORTLAND FM), GRANBY, MA

Nash Dinoland is a privately owned quarry in Granby, MA, in which 1.3m of Early Jurassic (ca. 200MA) Portland Formation rock is exposed. Sediments at the site were deposited in a shallow lake, and oscillation ripple marks are pervasive on exposed beds. Hundreds of footprints and trackways are exposed in situ, and many more are preserved in the small museum adjacent to the quarry. The large number of footprints and trackways at the site permits detailed analysis of population structure and trackway orientations relative to paleoshorelines. Furthermore, the large number of well-preserved theropod dinosaur footprints varying in size provides a substantial data set with which to test the hypothesis that the Grallator-Anchisauripus-Eubrontes plexus forms a morphological continuum.

In addition to the three theropod ichnotaxa already mentioned, the ornithischian print Anomoepus is also present. Grallator is the most abundant ichnotaxon, followed by Anchisauripus, Eubrontes, and Anomoepus. This indicates a population of predominantly carnivorous theropod animals, with scarce herbivorous ornithischians. No reason is evident for the unusually high carnivore: herbivore ratio, but the ratio is consistent with ratios recorded at other Connecticut River Valley sites. Azimuth orientations of 300+ footprints and trackways were measured in order to analyze trends in animal movement. Trackway distributions for all four ichnotaxa are bimodal with maxima approximately 140º apart. Many of the trackways trend approximately parallel to the ripple marks, suggesting that the animals were following the lake shoreline.

Length and digit III projection were measured for 39 theropod tracks and plotted to determine how these parameters varied relative to each other. The plot shows that digit III is relatively shorter in bigger footprints, which is consistent with observations made by Olsen (1980), who suggested that the different theropod ichnotaxa may represent a single species at various growth stages, rather than a different species track maker for each ichnotaxon. However, there is a conspicuous gap in the data, with few tracks of intermediate size being found. This gap may be due to poor preservation of intermediate footprint sizes rather than their absence, but further data collection is needed to test this hypothesis.