# Computational Approaches and Observer Variation in the 3D Musculoskeletal Modeling of the Heads of Anolis

## TL;DR

This paper explores new 3D modeling techniques to study the musculoskeletal anatomy of two Anolis lizard species, highlighting the repeatability and potential of these methods for evolutionary research.

## Contribution

The study introduces and evaluates novel 3D modeling approaches for quantifying musculoskeletal variation in Anolis lizards, including muscle segmentation and attachment mapping.

## Key findings

- 3D modeling techniques like DiceCT segmentation and surface attachment mapping are repeatable and accessible for musculoskeletal analysis.
- The study provides new data on jaw muscle volumes and fiber architecture in A. pulchellus and A. sagrei.
- Sexual dimorphism in skull anatomy is observed, offering insights into evolutionary and biomechanical adaptations.

## Abstract

High-resolution imaging, 3D modeling, and quantitative analyses are equipping evolutionary biologists with new approaches to understanding the variation and evolution of the musculoskeletal system. However, challenges with interpreting DiceCT data and higher order use of modeled muscles have not yet been fully explored, and the error in and accuracy of some digital methods remain unclear. West Indian Anolis lizards are a model clade for exploring patterns in functional adaptation, ecomorphology, and sexual size dimorphism in vertebrates. These lizards possess numerous jaw muscles with potentially different anatomies that sculpt the adductor chamber of the skull. Here we test approaches to quantifying the musculoskeletal shape of the heads of two species of Anolis: A. pulchellus and A. sagrei. We employ comparative approaches such as DiceCT segmentation of jaw muscles, 3D surface attachment mapping, and 3D landmarking with the aim of exploring muscle volumes, 3D muscle fiber architecture, and sexual dimorphism of the skull. We then compare sources of measurement error in these 3D analyses while also presenting new 3D musculoskeletal data from the Anolis feeding apparatus. These findings demonstrate the accessibility and repeatability of these emerging techniques as well as provide details regarding the musculoskeletal anatomy of the heads of A. pulchellus and A. sagrei which show potential for further research of comparative biomechanics and evolution in the clade.