Footprints, Trackways, and Hip Heights of Bipedal Dinosaurs—Testing Hip Height Predictions with Computer Models

Abstract

Three-dimensional, dynamic, computer models of the pelvis and hind limbs of theropods and ornithopods are used to produce synthetic trackways using a range of gait angles and degrees of limb joint flexion. The hip heights of the modeled stances are compared with the predictions of hip heights computed with various formulae that incorporate parameters measured from footprints and trackways. The tested formulae include: 4*footprint-length and other morphometric methods where the coefficients vary according to the size and taxonomic group of the inferred trackmaker, allometric methods with size and taxon specific coefficients and exponents, and pace-length divided by 0.6. The best fit (least difference) between model and predicted hip heights is achieved with the simple 4*footprint-length formula. The pace-length formula also works well, but only for a very narrow gait range. With one exception, a small theropod, the variable morphometric and allometric formulae consistently overestimate the hip heights in all case. For large theropods and ornithopods the overestimates can be up to 84% in extreme cases. There was also a trend for the magnitudes of overestimation to increase with increasing size of the trackmaker. The overestimates of hip height using these methods results in underestimation of the computed velocities attributed to the dinosaurs that made the trackways.