Sensitivity analysis in evolutionary robotic simulations of bipedal dinosaur running

Abstract

ABSTRACT-Constructing musculoskeletal models of extinct vertebrates requires subjective assumptions about soft tissue parameters rarely preserved in the fossil record. Despite these necessary assumptions about fundamental input values, paleobiologists rarely perform objective tests of best-estimate models before reaching conclusions based on predicted results. The extent to which lack of knowledge on soft tissue anatomy limits the accuracy of running speed estimates of extinct dinosaurs is therefore poorly understood. In this study, a sensitivity analysis is performed on an evolutionary robotics model of the non-avian theropod dinosaur Allosaurus, used previously to estimate maximum running speed in this extinct animal. A range of muscle parameters were varied over the range observed in extant vertebrates, whereas mass-related parameters were altered across the range of published estimates for Allosaurus. Muscle parameters have a linear relationship with maximum running speed, whereas surprisingly total body mass and torso center of mass have little effect. Muscle force values produced the greatest range in predicted running speeds (4.5-10.7 m/s) and stride lengths (4-5.8 m) in the sensitivity analysis, equating to 65.9% and 30.7% variation about the original 'best-estimate' prediction, a relatively high potential margin of error. These results highlight the importance of sensitivity analyses in biomechanical modeling of extinct taxa, particularly where values for soft tissues parameters are not tightly constrained. The current range in plausible values for soft tissue properties makes a robust quantitative assessment of behavioral ecology and species interactions in dinosaurian communities extremely difficult.

Disparity and convergence in bipedal archosaur locomotion

“…Where fossilized osteology is similar, along with estimatable parameters such as muscle moment arms, as we have shown to be the case with bipedal pseudosuchians and non-avian theropods (figures 3 and 4), then more detailed tests of functional disparity and convergence may be extremely difficult owing to large (hence overlapping) error bars on predictions [9,34]. However, where gross anatomy differs more considerably, then functional disparity may be more robustly established.…”

“…Sophisticated computational simulations are now commonly used to study detailed muscle dynamics and locomotion in living animals, and recently some of these approaches have been used to explore aspects of gait and performance in fossil species [32][33][34]. The challenge facing palaeobiologists and biomechanicists attempting to construct these models for extinct archosaurs clearly lies in defining muscle properties (inputs into biomechanical models) in a meaningful and objective way.…”

“…Where attempts have been made to simulate locomotion in extinct archosaurs, redundancies in muscle input values have been addressed using sensitivity analyses; plausible ranges for input values, rather than single values, are tested resulting in a spectrum of gait predictions [33,34]. Where fossilized osteology is similar, along with estimatable parameters such as muscle moment arms, as we have shown to be the case with bipedal pseudosuchians and non-avian theropods (figures 3 and 4), then more detailed tests of functional disparity and convergence may be extremely difficult owing to large (hence overlapping) error bars on predictions [9,34].…”

Reconstructing pectoral appendicular muscle anatomy in fossil fish and tetrapods over the fins‐to‐limbs transition

“…Reconstructions of soft tissue anatomy are equally important as those of the skeleton because they can provide crucial information about locomotion, mode of life, and ecology of extinct animals (Witmer, 1995). For example, muscle reconstructions have been used to infer characteristics such as posture, maximum speed, and even possible gaits in extinct vertebrates (Russell, 1972;Sumida, 1989;Hutchinson & Garcia, 2002;Sellers et al, 2004Sellers et al, , 2009Hutchinson et al, 2005;Sellers & Manning, 2007;Bates et al, 2010;Schachner, Manning & Dodson, 2011). In addition, the ancestral configuration of the limbs is critical for understanding how constraints and adaptations led to the morphological diversity of modern tetrapod limbs.…”

On the inference of function from structure using biomechanical modelling and simulation of extinct organisms

“…As model complexity increases (e.g. highly dynamic models of whole stride cycles), there is a similar increase in unknowns, but this problem is not impossible to deal with using broad sensitivity analyses [20].…”