SIZE VARIATION OF ANOMOEPUS TRACKS IN THE PORTLAND FORMATION AT DINOSAUR FOOTPRINT RESERVATION, HOLYOKE, MA

Anomoepus is an ornithischian ichnogenus found in the Lower Jurassic rocks of the Connecticut Valley (Newark Supergroup). They are particularly abundant in the Portland Formation exposed at Dinosaur Footprint Reservation (DFR), in Holyoke, MA. We conducted a detailed study of the size distribution of the tracks found along 34 separate trackways at the site and compared them to previously published Anomoepus trackway data from the older East Berlin Formation at the Gary Gaulin (GG) site, located 6.4 kilometers south of DFR (Dalman & Weems, 2013).

Track size, which was defined as the distance from the distal tip of digit III to the proximal end of the phalangeal pad, was the most reliable measurement and was used to assess differences in trackmaker size. Our 85 measurements exhibit a mean track size of 13.93 cm +/- 2.48 cm. The sizes of the tracks are normally distributed and suggest a population of animals with few small individuals. A comparison of our data with the size distribution data from the GG site reveals that the GG sizes (mean = 3.4 +/- 0.77 cm) are significantly smaller than those found at DFR.

Our preliminary explanations for the significant differences in size distribution at the sites are: 1) Different sized animals inhabiting different depositional environments represented by the two different formations; 2) Different sized, closely related species possibly inhabiting the Hartford Basin at different time intervals; 3) The GG site may be indicative of an ornithischian nesting ground; 4) The GG site might have been a site better suited to the preservation of small traces.