Maniraptoran pelvic musculature highlights evolutionary patterns in theropod locomotion on the line to birds

Abstract

Locomotion is a fundamental aspect of palaeobiology and often investigated by comparing osteological structures and proportions. Previous studies document a stepwise accumulation of avian-like features in theropod dinosaurs that accelerates in the clade Maniraptora. However, the soft tissues that influenced the skeleton offer another perspective on locomotory adaptations. Examination of the pelvis for osteological correlates of hind limb and tail musculature allowed reconstruction of primary locomotory muscles across theropods and their closest extant relatives. Additionally, the areas of pelvic muscle origins were quantified to measure relative differences within and between taxa, to compare morphological features associated with cursoriality, and offer insight into the evolution of locomotor modules. Locomotory inferences based on myology often corroborate those based on osteology, although they occasionally conflict and indicate greater complexity than previously appreciated. Maniraptoran pelvic musculature underscores previous studies noting the multifaceted nature of cursoriality and suggests that a more punctuated step in caudal decoupling occurred at or near the base of Maniraptora.

Three-dimensional polygonal muscle modelling and line of action estimation in living and extinct taxa

“…Furthermore, 3D reconstructions of the shape of individual muscles and the configuration of the musculature are enabled for extant taxa when only surface models and dissection data are available, thus facilitating further downstream analyses. Capturing surface data during a dissection, either through photogrammetry or other surface digitization techniques 1 , 83 – 87 , and reconstructing the musculature using our approach could streamline the pipeline for comparative morphological analyses 8 , 22 , 27 , 70 , 72 , 88 as well as biomechanical models and simulations. Our method enables the subject-specific quantification of muscle attachment area as well as muscle shape and path estimations, information usually lost during dissection, which, however, is crucial for musculoskeletal modelling 29 .…”

“…The centroids of the attachment areas can either be estimated for extinct taxa 44 , 50 , 51 , 53 , 60 , 97 , 122 – 124 or measured/inferred from digitized attachment areas of extant taxa 69 , 73 , 74 , 78 , 79 , 88 , 125 . Additionally, we developed a code (Supplementary Information) to streamline musculoskeletal modelling workflows that now allows to directly calculate the attachment centroids and the attachment area for extinct and extant taxa from the vertices placed on the attachment area during the iterative polygonal muscle modelling approach presented herein (see Supplementary Information for muscle attachment definition) or for selected faces of a segmented muscle (i.e., diceCT or MRI) or selected faces of a muscle scar/attachment area on a bone, as follows.…”

Anatomically grounded estimation of hindlimb muscle sizes in Archosauria

“…Bishop, Michel, et al, 2021;Gignac & Erickson, 2017;Herbst et al, 2022;Hutchinson, 2002;Snively et al, 2013;Snively & Russell, 2007). There remains plenty of room for improvement and innovation, as echoed by similar recent studies (Bates et al, 2021;Broyde et al, 2021;Rhodes et al, 2021).…”

“…The predictions made here may not scale into the largest archosaurian species, and broad comparative studies of archosaur hindlimb muscle area estimation (e.g. Demuth et al, 2022;Rhodes et al, 2021;Snively et al, 2019), and calculations using those data, will need reinvestigation with improved data on PCSA:AA (or volumetric) relationships.…”

Back to the bones: do muscle area assessment techniques predict functional evolution across a macroevolutionary radiation?

“…These muscle area assessment (MAA) techniques have been applied to limbs (e.g. [22][23][24]) and the axial skeleton (e.g. [25][26][27]) but are most frequently used in skulls (originating from the 'dry skull method' [1]) to examine masticatory evolution in both extinct and extant taxa (e.g.…”