AN EARLY JURASSIC NON-MARINE FOSSIL ASSEMBLAGE FROM THE PORTLAND FORMATION, HARTFORD BASIN, MASSACHUSETTS

The Lower Jurassic sandstones of the Hartford Basin are well known for their dinosaur trackways, but few studies have addressed the invertebrate faunas found there.  To begin to develop a more complete understanding of the ecology of these track-rich environments, a suite of invertebrate and vertebrate trace fossils from the Portland Formation in the Hoover Quarry, East Longmeadow, MA was examined.  Formerly known as the Hines Quarry, it is notable for being one of few sites where vertebrate skeletal material has been collected in the region, including the type specimen of Stegomosuchus longipes, a small herbivorous plated reptile.

Trace fossils occur as concave and convex hyporelief and epirelief, on bed soles and surfaces, in fine arenaceous to argillaceous red sandstone.  Invertebrate ichnogenera include Palaeophycus cf. tubularis, Planolites isp., Scoyenia cf. gracilis, and Skolithos isp., as well as a 75cm long, 2-3cm wide meandering to sinusoidal trace.  Two other problematic trace fossils also occur, including a set of small (<1cm diameter) stellate traces and a Skolithos-like vertical burrow terminated with an unusual pattern of overlapping scratches in varying orientations.  Vertebrate traces include theropod dinosaur footprints referable to Eubrontes.  The type specimen of S. longipes displays a similar Skolithos-dominated assemblage on its upper and lower surface; however, the burrows do not seem to penetrate to the horizon containing the skeletal remains.

Polygonal desiccation cracks, mud curls, clay drapes, and asymmetric ripples on trace-bearing surfaces are consistent with deposition in a shallow aquatic environment that was periodically emergent.  Viewed in the context of previously studied nearby sections of the Portland Formation, Hoover Quarry exposures could have been deposited in a playa, shallow lacustrine or fluvial environment.  Hoover traces are typical of the Scoyenia ichnofacies, which is common in continental firmground environments.