Poster Session I (Wednesday, October 26, 2016, 4:15–6:15 PM)
TRACKWAY EVIDENCE FOR A THEROPOD GROUP ATTACK UPON A POSSIBLE CERATOPSIAN DINOSAUR FROM THE MORENO HILL FORMATION (TURONIAN) NEW MEXICO
WOLFE, Douglas G., White Mountain Dinosaur Exploration Center, Greer, AZ, United States of America; WOLFE, Hazel D., White Mountain Dinosaur Exploration Center, Greer, AZ, United States of America
Track impressions upon a fallen sandstone block reveal multiple three-toed (theropod) dinosaur tracks; associated with a large, shallowly-impressed, circular track exhibiting the pedal architecture of a quadrupedal, possibly ceratopsian, ornithischian. The track site lies near, and stratigraphically slightly above, the Moreno Hill Formation (Turonian) dinosaur type localities (the Zuni Fauna), including Zuniceratops, Nothronychus, Jeyawati and a new theropod dinosaur currently under study. The track surface is a silty-muddy interval atop the lower of two prominent and widely persistent channel sandstones; the track surface now lies perpendicular to horizontal. The theropod tracks are “muddy”; deeply impressed into a water-rich substrate which slumped into the impressions, while also preserving features such as claw impressions. Mapping the three-toed tracks reveals at least three sizes (up to 33.5 cm wide) of tri-dactyl tracks (including a matched stride-pair) exhibiting a wide inter-digit angle and morphology comparable with theropods such as tyrannosauroids. Several of the theropod tracks are oriented toward, and then away from, the posterior margin of the circular track. The ungual impressions of the circular (approximately 34 cm) track suggest rapid movement away from the oncoming three-toed tracks. The circular track is less impressed into the substrate than the three-toed tracks, apparently more buoyant on the muddy substrate. The assemblage of tracks appears a rare example of positive evidence for a co-operative and active pursuit by a group of theropod predators, (possibly tyrannosauroid), upon an equally large four-legged (possibly ceratopsian) dinosaur. The sandstone surface nearby preserves swimming tail/track impressions interpreted as crocodilian, in-situ tree stumps are documented in nearby finer-grained facies, the Zuniceratops holotype coracoid contains D-shaped bite penetrations with surface checking of the elements suggesting inundation-desiccation, and the Zuniceratops bonebed was deposited within a “log-jam” channel deposit. Together these data demonstrate a close association between submerged and emergent environments with predator and prey elements interacting at the margins. Zuniceratops (or other quadrupedal ornithischian) probably sought shelter from more land-bound predators by risking danger within crocodile-inhabited wetlands, as do many modern terrestrial herbivores.