Geometric morphometrics in herpetology: modern tools for enhancing the study of morphological variation in amphibians and reptiles
The use of geometric morphometrics for studying phenotypic variation in amphibians and reptiles has visibly increased in the last decade. These modern tools provide a robust statistical framework to study organismal shape while preserving the geometric properties of the studied structures and thus improve our capacity for investigating patterns of morphological variation, and understanding their ecological and historical causes. Their application in herpetology has shed new light to the remarkable diversity observed among extant and extinct amphibians and reptiles. Here I first briefly consider the historical emergence of geometric morphometric methods, trying to provide a practical guide for herpetologists interested in implementing these tools to their investigation. I then review the wide array of published studies using geometric morphometrics to investigate morphological patterns in amphibians and reptiles. Across different investigation fields, an emergent pattern is the existence of general similarities, but also profound differences, among members of higher taxonomic groups. Size-shape allometry is a common pattern in many groups, but remarkable variation of allometric trajectories exists among closely related taxa. Sexual dimorphism has been extensively studied in reptiles, but less so in amphibians, while the contrary is true for phenotypic plasticity. The use of geometric morphometrics has allowed the detection of potentially adaptive shape patterns and the investigation of their causes. Finally, these methods have been invaluable in the study of fossils and have provided a better understanding of the paleobiology of extinct taxa.