Comparative Three‐Dimensional Moment Arm Analysis of the Sauropod Forelimb: Implications for the Transition to a Wide‐Gauge Stance in Titanosaurs

Abstract

The evolution of extraordinarily large size among Sauropoda was associated with a number of biomechanical adaptations. Changes in muscle moment arms undoubtedly accompanied these adaptations, but since muscles rarely fossilize, our ability to understand them has been restricted. Here, we use three‐dimensional (3D) musculoskeletal modeling to reconstruct and quantitatively assess leverage of forelimb muscles in the transition from the narrow‐gauge stance of basal sauropods to a wide‐gauge stance in titanosaurs. A comparative analysis is conducted on three neosauropods: the narrow‐gauge diplodocid Apatosaurus louisae, the intermediate‐gauge titanosariform Giraffatitan brancai, and the wide‐gauge titanosaur Diamantinasaurus matildae. In this study, moment arm magnitudes and corresponding morphological evidence indicates multiple changes across the narrow‐gauge to wide‐gauge transition in sauropods. High shoulder adduction was found in Diamantinasaurus, suggesting functional changes for supporting a wider stance and a limb less aligned with ground reaction force. High leverage in shoulder extension of Diamantinasaurus and Giraffatitan is possibly related to the increased use of the forelimb in forward propulsion with an anterior shift in center of mass. In addition, the prominence of the olecranon process in Diamantinasaurus produced high moment arm leverage in elbow flexion and extension, suggesting titanosaurs might have maintained a more flexed forelimb posture and displayed an increased degree of maneuverability. Other results are more variable between taxa but still indicate smaller scale changes. A sensitivity analysis was also conducted to measure the reliability of our models and test specific uncertainties within the modeling process, as well as other uncertainties uncovered during analysis. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:794–817, 2019. © 2018 Wiley Periodicals, Inc.

Myological reconstruction of the pelvic girdle and hind limb of the giant titanosaurian sauropod dinosaur Dreadnoughtus schrani

“…Scarcity of myological investigations of sauropods, in general, including well‐preserved and fairly complete titanosaurian taxa (e.g., Rapetosaurus , Curry Rogers, 2009; Saltasaurus , Powell, 2003), combined with a general lack of quantity and quality of preservation for the clade as a whole, has greatly limited our understanding of titanosaurian appendicular musculature. Only a few previous species‐level myological studies have been completed for members of Titanosauria (Borsuk‐Bialynicka, 1977; Ibiricu et al, 2018; Klinkhamer et al, 2018, 2019; Otero & Vizcaíno, 2008; Voegele et al, 2020). Alternatively, descriptions of sauropod appendicular material occasionally include discussion of probable osteological correlates for muscle attachment (e.g., Curry Rogers, 2009; Gallina & Apesteguía, 2015; Harris, 2007; Silva Junior et al, 2019).…”

“…The term ‘wide‐gauge’ was originally proposed (by Farlow, 1992) for sauropod trackways in which the footfalls are placed well away from the body midline, presumably due in part to widening of the pectoral and pelvic girdles (Henderson, 2006; Ullmann et al, 2017; Wilson & Carrano, 1999). Although titanosaurians are often collectively referred to as wide‐gauge in body width (e.g., Klinkhamer et al, 2018, 2019; Vila et al, 2013), gauge may vary through sauropod ontogeny (Lockley et al, 2002). Additionally, trackways have recently been discovered which vary between narrow‐ and wide‐gauge along the same path, possibly due to behavior (e.g., Castanera et al, 2012; Meyer et al, 2018; Stevens et al, 2016), and wide‐gauge trackways have been found in Jurassic deposits that presumably predate the origin of Titanosauria (e.g., Romano et al, 2007, and references therein).…”

“…The appendicular skeleton of Dreadnoughtus is conducive to detailed myological study because: (1) at least one of every stylopodial and zeugopodial element is preserved between the holotype and paratype individuals and; (2) these bones retain excellent surface texture, including numerous osteological correlates (Lacovara et al, 2014; Ullmann & Lacovara, 2016). Furthermore, Dreadnoughtus is significantly larger bodied than other titanosaurians for which myological data are currently available, and in cladistic analyses this giant taxon often occupies a moderately derived phylogenetic position compared to those of related taxa with reconstructed myology: Opisthocoelicaudia (Borsuk‐Bialynicka, 1977); Neuquensaurus (Otero & Vizcaíno, 2008); Epachthosaurus (Ibiricu et al, 2018); and Diamantinasaurus (Klinkhamer et al, 2018, 2019).…”

“Keep your feet on the ground”: Simulated range of motion and hind foot posture of the Middle Jurassic sauropod Rhoetosaurus brownei and its implications for sauropod biology

“…With body masses exceeding 40 t (Alexander, ; Benson et al, ; Bonaparte & Coria, ; Lacovara et al, ; Mazzetta, Christiansen, & Fariña, ), one might ask how these gigantic animals could move, let alone support themselves, without their bones failing under such heavy loads. Many studies have reconstructed sauropod locomotion using a variety of approaches, including comparative osteology (e.g., Carrano, ; Christiansen, ; Hay, ; Sander et al, ), paleoichnological analysis (e.g., Wilson, ; Wilson & Carrano, ), biomechanical investigations (e.g., Christian, Heinrich, & Golder, ; Klinkhamer, Mallison, Poropat, Sloan, & Wroe, ; Preuschoft, Hohn‐Schulte, Stoinski, & Witzel, ), and/or computational techniques (e.g., Sellers, Margetts, Coria, & Manning, ). In sum, the majority of these studies proposed that sauropods likely had fairly restricted limb movements with reduced mobility at the main joints.…”

A diverse Late Cretaceous vertebrate tracksite from the Winton Formation of Queensland, Australia

“…Both Diamantinasaurus and Savannasaurus had manual phalanges (Hocknull et al, 2009;Poropat et al, 2015b;Poropat et al, 2016;Poropat et al, 2020), and a manual phalangeal formula of 2-1-1-1-1-including a prominent ungual phalanx on digit I-has been proposed for Diamantinasaurus specifically (Hocknull et al, 2009;Poropat et al, 2015b). Furthermore, both Diamantinasaurus and Savannasaurus had wide-gauge stances (Klinkhamer et al, 2018;Klinkhamer et al, 2019;Poropat et al, 2015b;Poropat et al, 2016;Poropat et al, 2020). Thus, one of these taxa might have been the AODF 904.S1 trackmaker.…”