School of Earth, Atmospheric and Environmental Science, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK.
J R Soc Interface. 2011 Aug 7;8(61):1142-54. doi: 10.1098/rsif.2010.0634. Epub 2011 Jan 13.
Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. 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 tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology.
采用有限元分析法研究了由于体重而导致遗迹化石记录出现偏差的程度。在各种基质条件下，针对四种不同体型的恐龙类群（Struthiomimus、Tyrannosaurus、Brachiosaurus 和 Edmontosaurus）模拟了虚拟足迹。根据骨骼学和已发表的软组织重建，生成了足迹的足印轮廓。将垂直于相当于动物体重的脚部施加负载，并根据需要相应地分配到前肢和后肢。理想的半无限弹性塑性基质具有“恰到好处”的品质，只有在一个狭窄的负载范围内才能产生足迹，因为小型动物无法使基质凹陷，而较大的动物如果不陷入困境，就无法在该区域穿行。如果假设存在一个坚硬的地下层，则可能会形成更完整的组合，尽管存在强烈的偏向于较大、较重动物的倾向。组合中化石足迹的深度可能表明在形成足迹时机械上不同的基质层的厚度，即使石化地层在成分上看起来是均匀的。这项工作提高了利用脊椎动物足迹作为古环境指示物的有效性，从而可以推断出形成足迹时的基质条件。此外，还检查了模拟的下足迹，并表明足部下的复杂变形可能并不像以前解释的那样是肢体运动学的指示，而是足迹底部的脊和波动可能是沉积物位移矢量和足形态的函数。
