Anatomy of a Jurassic Theropod Trackway from Ardley, Oxfordshire, U.K.

Abstract

Ardley Quarry, Oxfordshire, central England, preserves a most remarkable ichnological record of dinosaur activity on a single 168 Ma old trackway-bearing horizon. This horizon reveals over 40 dinosaur trackways, most of them sauropod, but including several giant theropod trackways tentatively attributed to Megalosaurus, the first creature of its kind recognized and assigned to Dinosauria. A 60 meter-long portion of one theropod trackway (no. 80) is systematically characterized in terms of pitch, yaw, and roll of successive footprints. Variations among these parameters correspond closely with acceleration/deceleration intervals in the trackway, impressed by the animal in wet calcareous mud within the tidewater zone of a mid-Jurassic coastal plain. Energy expended (1.4 watts) by the animal in making each footprint in the trackway is comparable to the resting metabolic rate of modern birds and mammals. Efforts by the theropod 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. Maximum positive yaw (outward from the midline of the trackway) generally corresponds with forward pitch. Positive yaw is greatest where positive (outward) roll is maximum. 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.