ANATOMY OF A JURASSIC THEROPOD TRACKWAY FROM ARDLEY, OXFORDSHIRE, U.K

Ardley Quarry, Oxfordshire, central England, preserves a most remarkable ichnological record of dinosaur activity on a single 163 Ma old trackway-bearing horizon. Opened for a brief moment in geologic time, this presently exhumed sub-horizontal window on the Jurassic reveals over 40 dinosaur trackways, most of them sauropod, but including several giant theropod trackways attributed to Megalosaurus, one of the first creatures assigned to Dinosauria. Despite ongoing quarrying and follow-up landfill operations, which have reburied the world’s largest set of theropod footprints that show running (Trackway 13), portions of at least two other theropod trackways were accessible in 2002. A 60 metre-long portion of one of these (Trackway 80) has been systematically characterized in terms of pitch, yaw, and roll of successive footprints. In Trackway 80, the trackmaker, keenly aware of the unstable ground conditions, maintained a wide gauge trackway while simultaneously making repeated efforts to accelerate, as shown by changes in direction of travel and stride length. Efforts to accelerate are reflected by intervals of forward pitch of footprints; here the backward component of the force exerted upon the ground exceeds the forward component. Conversely, during braking (deceleration) intervals, footprints tend to exhibit a backward pitch in which the forward component of the force will have exceeded the backward component. Measurements of pitch, yaw, and roll of dinosaur footprints hold potential for revealing fundamental locomotor characteristics of dinosaurs and for estimating acceleration and speed of an animal from its footprint record. Knowing from skeletal remains the mass (and weight) of an adult theropod it remains to determine the force exerted by its feet upon the ground during acceleration. Realistic estimates of F in the equation F=ma could be derived by analogue experiments along a modern coastal plain thereby providing independent estimates of dinosaur speeds.