Goldilocks and Dinosaur tracks

Finite-element analysis was used to investigate the extent of bias in the ichnological fossilrecord attributable to body mass. Virtual tracks were simulated for four dinosaur taxa ofdifferent sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in arange of substrate conditions. Outlines of autopodia were generated based upon osteologyand published soft-tissue reconstructions. Loads were applied vertically to the feet equivalentto the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant.Ideal, semi-infinite elastic–plastic substrates displayed a 'Goldilocks' quality whereonly a narrow range of loads could produce tracks, given that small animals failed toindent the substrate, and larger animals would be unable to traverse the area without becomingmired. If a firm subsurface layer is assumed, a more complete assemblage is possible,though there is a strong bias towards larger, heavier animals. The depths of fossil trackswithin an assemblage may indicate thicknesses of mechanically distinct substrate layers atthe time of track formation, even when the lithified strata appear compositionally homogeneous.This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicatorsin terms of inferring substrate conditions at the time of track formation. Additionally,simulated undertracks are examined, and it is shown that complex deformation beneath thefoot may not be indicative of limb kinematics as has been previously interpreted, but insteadridges and undulations at the base of a track may be a function of sediment displacement vectorsand pedal morphology.

This article has been published, and the full reference for the paper is:

Falkingham, P.L., Bates, K.T., Margetts, L., and Manning, P.L. 2011 The 'Goldilocks' effect: preservation bias in vertebrate track assemblages. Journal of The Royal Society Interface.

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Brachiosaur tracks simulated with ParaFEM