However, these approaches yield very broad ranges for soft tissue parameters in dinosaurs which translates directly into imprecise values for performance estimates like running speed ( Bates et al., 2010). Typically, minimum and maximum bounds are placed on such parameters based on data from living animals ( Hutchinson, 2004a Hutchinson, 2004b Hutchinson & Garcia, 2002) and/or additional computer models ( Bates, Benson & Falkingham, 2012 Bates et al., 2010 Hutchinson et al., 2005 Sellers et al., 2013). These soft tissue parameters are almost never preserved in dinosaur fossils and therefore need to be estimated indirectly. Biomechanical approaches emphasize the well-known scaling principles ( Biewener, 1989 Biewener, 1990) that animals of larger body mass have more restricted locomotor performance because muscle mass scales isometrically, but muscle force, relative speed of contraction and power scale with negative allometry ( Alexander, 1977 Alexander & Jayes, 1983 Marx, Olsson & Larsson, 2006 Medler, 2002).īiomechanical models inherently incorporate anatomical characters (e.g., limb proportions) on which more traditional qualitative assessments are based, but also require quantitative definitions for soft tissue parameters associated with mass distribution and muscle properties. In contrast, more direct and quantitative biomechanical approaches have favoured intermediate ( Farlow, Smith & Robinson, 1995 Sellers & Manning, 2007) or much slower speeds for T. rex, with the latter including within their predictive range an inability to reach true running gaits ( Gatesy, Baker & Hutchinson, 2009 Hutchinson, 2004b Hutchinson & Garcia, 2002). These studies cite the long and gracile limbs of T. rex as a key adaptive feature indicative of high relative ( Christiansen, 1998) and absolute speeds ( Bakker, 1986 Paul, 1998 Paul, 2008), along with possession of large tail-based hip extensor musculature ( Persons & Currie, 2011). Some qualitative anatomical studies ( Bakker, 1986 Paul, 1998 Paul, 2008), including some employing a degree of quantitative biomechanical methods ( Paul, 1998), have proposed very fast running speeds (up to 20 ms −1) and an overall high degree of athleticism for large theropods like T. rex. However, despite a century of research since Osborn’s (1916) work on tyrannosaur limb anatomy there remains no consensus on the most accurate maximum speeds for T. rex, or indeed whether or not its gigantic body size prohibited running completely. The running ability of T. rex and other similarly giant dinosaurs has been intensely debated in the literature ( Bakker, 1986 Hutchinson & Garcia, 2002 Paul, 1998 Paul, 2008 Sellers & Manning, 2007) and features prominently in reconstructions of the lifestyles and carnivorous behaviours of large theropod dinosaurs ( Bakker, 1986 Carbone, Turvey & Bielby, 2011 Farlow, 1994 Holtz Jr, 2008 Paul, 1998 Paul, 2008 Ruxton & Houston, 2003). Tyrannosaurus rex is one of the largest bipedal animals to have ever evolved and as such it represents a useful model organism for understanding morpho-functional adaptations and constraints at multi-tonne body sizes ( Brusatte et al., 2010). rex, and demonstrates the power of multiphysics approaches for locomotor reconstructions of extinct animals. Being limited to walking speeds contradicts arguments of high-speed pursuit predation for the largest bipedal dinosaurs like T. rex-long argued to indicate competent running ability-would actually have mechanically limited this species to walking gaits. Combining these two approaches reduces the high-level of uncertainty in previous predictions associated with unknown soft tissue parameters in dinosaurs, and demonstrates that the relatively long limb segments of T. Here we present a new approach that combines two separate biomechanical techniques (multibody dynamic analysis and skeletal stress analysis) to demonstrate that true running gaits would probably lead to unacceptably high skeletal loads in T. Different studies using differing methodologies have produced a very wide range of top speed estimates and there is therefore a need to develop techniques that can improve these predictions. The running ability of Tyrannosaurus rex has been intensively studied due to its relevance to interpretations of feeding behaviour and the biomechanics of scaling in giant predatory dinosaurs.
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