Grallator Hitchcock 1858

Ichnogenus Grallator Hitchcock, 1858 Referred specimens: UWGM 7435, a partial right pes trace preserved in concave epirelief was collected in the upper Jelm Formation along the Red Wall, Natrona County, Wyoming; UWGM ‘Jelm Dino Track’ site (Fig. 5). Description: UWGM 7435 is a small (9.0 × 5.6 cm) partial pes impression preserving digits II–IV and, potentially, a very faint manus impression. The isolated slab was found ex situ, though confidentlyconstrainedto 1–2 mofstratigraphicthickness (topographic constraint) ~ 15 m below the top of the Jelm Formation. The track is located on a 21.5 × 12-cm slab of fluvial sandstone with broad-wavelength, ripple-marked bedding; the preserved trace is digitigrade and tridactyl, mesaxonic where digit III is longest and potentially quadrupedal (Fig. 5). The pes digits are relatively straight, long, and slender with small acuminate claw impressions. Pads are observable, but not sharply defined. Digit IV is closely aligned to III with a 7.5° divarication. Digit III to II has just over double the divarication (17°). The impression of digit IV is c. 8 mm wide with little variance, while digits III and II are c. 13 and 11 mm, respectively. Although lacking morphological details, a faint impression anterolateral to pes digits II–III is interpreted to be a manus with three anterolaterally projected digits. Because of this ambiguity in manus identification, we consider this trace within the Atreipus – Grallator plexus, but cannot confidently assign it to either Atreipus or Grallator. Considering the ecological implications of a Grallator (i.e. dinosaurian) tracemaker, we conservatively assign this trace to Atreipus.