The repeated evolution of convergent or analogous traits is often used as evidence for adaptive evolution. Squamate reptiles show a high degree of convergence in a variety of morphological traits; however, the evolutionary mechanisms driving these patterns are not fully understood. Here we investigate the evolution of tail spines, a trait that evolved multiple times in evolutionarily independent clades of lizards. Taking a comparative phylogenetic approach, we use 2877 squamate species to demonstrate that the...