Testing Convergent and Parallel Adaptations of Talpids Humeral Mechanical Performance by means of Geometric Morphometrics and Finite Element Analysis

The shape and mechanical performance of Talpidae humerus were studied by means of Geometric Morphometrics and Finite Element Analysis in both extinct and extant taxa. The aim of this study was to test whether the ability to dig complex tunnel systems, quantified by humerus mechanical performance, was characterized by convergent or parallel adaptations in different groups of complex tunnel digger within Talpidae, i.e. Talpinae+Condylura (monophyletic) and some complex tunnel diggers not belonging to this clade. Our results suggest that the pattern underlying Talpidae humerus evolution is evolutionary parallelism. However, these results changed to true convergence when Condylura was moved to a more basal phylogenetic position as indicated by some molecular analyses. Shape and performance analyses, as well as specific comparative methods, allowing the estimation of ancestral states, provided strong evidence that the ability to dig complex tunnels reached a functional optimum in distantly related taxa. This was also confirmed by the lower phenotypic variance in complex tunnel digger taxa, compared to non complex tunnel diggers. Evolutionary rates of phenotypic change showed a smooth deceleration in correspondence with the most recent common ancestor of Talpinae+Condylura clade.