Variability of stepping characteristics in sauropods

Introduction In quadrupeds, the motor repertoire of the forelimbs is typically more diverse than that of the hindlimbs due to more pronounced supraspinal control. This greater supraspinal control may manifest as lesser automaticity in forelimb movements during a relatively simple motor task, such as locomotion. The degree of automaticity can be estimated by the variability of certain movement parameters. However, such variability is rarely assessed separately for the forelimbs and hindlimbs. Sauropods appear to be the only group of animals for which, based on available data, it is possible to estimate the variability of stepping parameters for both the forelimbs and hindlimbs. Methods The forelimb and hindlimb stride length and step width were measured using outline drawings of 27 relatively long sauropod trackways. Their coefficients of variation were then calculated. Results An analysis of trackways revealed significant differences in the variability of step width and stride length between the forelimbs and hindlimbs for some trackways. In some cases, the stepping parameters of the hindlimbs were more variable. Significant negative correlations were found between estimated walking speed and (i) the coefficient of variation of forelimb stride length and (ii) the coefficient of variation of hindlimb step width. Conclusions These findings are consistent with a greater contribution of hindlimb-related mechanisms to locomotor organization in sauropods compared with several extant quadrupedal taxa.