A toolbox for the retrodeformation and muscle reconstruction of fossil specimens in Blender

Abstract

Accurate muscle reconstructions can offer new information on the anatomy of fossil organisms and are also important for biomechanical analysis (multibody dynamics and finite-element analysis (FEA)). For the sake of simplicity, muscles are often modelled as point-to-point strands or frustra (cut-off cones) in biomechanical models. However, there are cases in which it is useful to model the muscle morphology in three dimensions, to better examine the effects of muscle shape and size. This is especially important for fossil analyses, where muscle force is estimated from the reconstructed muscle morphology (rather than based on data collected in vivo ). The two main aims of this paper are as follows. First, we created a new interactive tool in the free open access software Blender to enable interactive three-dimensional modelling of muscles. This approach can be applied to both palaeontological and human biomechanics research to generate muscle force magnitudes and lines of action for FEA. Second, we provide a guide on how to use existing Blender tools to reconstruct distorted or incomplete specimens. This guide is aimed at palaeontologists but can also be used by anatomists working with damaged specimens or to test functional implication of hypothetical morphologies.

Anatomically grounded estimation of hindlimb muscle sizes in Archosauria

“…In recent years there has indeed been a major push from not just identifying muscle attachments for extinct animals, but quantifying muscle sizes and forces driven primarily by enhanced computer modelling of feeding and locomotor behaviours (e.g. Bishop, Cuff, et al, 2021 ; Bishop, Falisse, et al, 2021 ; 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 ).…”

“…They found good agreement between their estimates and dissection‐based muscle mass measurements for crocodile hindlimb and gorilla shoulder muscles; and applied this method to the hindlimbs of the Triassic archosaurifom Euparkeria capensis . This approach (similar to the volumetric method of Herbst et al, 2022 ) is an attractive alternative, or complementary method; indeed, all methods could be complementary.…”

Assessing the adductor musculature and jaw mechanics of Proterochampsa nodosa (Archosauriformes: Proterochampsidae) through finite element analysis

“…The scans were processed using the software AVIZO within which, among other structures, the mandible of Proterochampsa was digitally segmented and virtually isolated from the skull (de Simão‐Oliveira et al, 2022a, 2022b). Afterwards, the mandible of Proterochampsa was reconstructed and retrodeformed using the software MeshMixer and Blender, following the protocols suggested by Lautenschlager et al (2016) and Herbst et al (2022). Due to the incompleteness of the skull of the specimen (de Simão‐Oliveira et al, 2022a), it was only employed to model the parameters of the adductor musculature, but not submitted to the Finite Element Analyses (FEA).…”

Modern three-dimensional digital methods for studying locomotor biomechanics in tetrapods

“…These musculoskeletal models (see Glossary) normally are grounded in empirical data such as dissections or 3D imaging of soft tissue morphology (e.g. Brown et al, 2003 ; Nagano et al, 2005 ; Zarucco et al, 2006 ; Hutchinson et al, 2015 ; Charles et al, 2016 ; Regnault and Pierce, 2018 ; Sullivan et al, 2019 ; Bishop et al, 2021b ; Wiseman et al, 2021 ; Collings et al, 2022 ), or a 3D polygonal modelling approach ( Demuth et al, 2022a ; Herbst et al, 2022b ), and are sometimes placed within a phylogenetic context ( Brocklehurst et al, 2022 ; Löffler et al, 2022 ). Musculature must be reconstructed if the research question pertains to the moment arms (see Glossary), moment-generating capacity and/or activation of specific muscles/muscle groups.…”