A landmarking protocol for geometric morphometric analysis of squamate endocasts

Abstract

Landmark‐based geometric morphometrics is widely used to study the morphology of the endocast, or internal mold of the braincase, and the diversity associated with this structure across vertebrates. Landmarks, as the basic unit of such methods, are intended to be points of correspondence, selected depending on the question at hand, whose proper definition is essential to guarantee robustness and reproducibility of results. In this study, 20 landmarks are defined to provide a framework to analyze the morphological variability in squamate endocasts. Ten species representing a cross‐section of the diversity of Squamata from both phylogenetic and ecological (i.e., habitat) perspectives were considered, to select landmarks replicable throughout the entire clade, regardless of the degree of neuroanatomical resolution of the endocast. To assess the precision, accuracy, and repeatability of these newly defined landmarks, both intraobserver and interobserver error were investigated. Estimates of measurement error show that most of the landmarks established here are highly replicable, and preliminary results suggest that they capture aspects of endocast shape related to both phylogenetic and ecologic signals. This study provides a basis for further examinations of squamate endocast disparity using landmark‐based geometric morphometrics.

Endocast, brain, and bones: Correspondences and spatial relationships in squamates

“…This indicates that areas with a close correspondence between the brain and endocranial surface can potentially exhibit deviations in shape; however, the typical degree and pattern of such divergences remain to be tested. By employing landmark‐based geometric morphometric methods (e.g., Allemand et al, 2023; Watanabe, Gignac, et al, 2019), future quantitative assessments of brain–endocast correspondence in shape will help us to understand which brain regions are accurately or poorly approximated by the corresponding areas on squamate endocasts. Such analyses will have important implications for accurate and precise inferences of brain morphology from squamate endocasts.…”