Tempo and mode of evolution across multiple traits in an adaptive radiation of birds (Vangidae)

An ongoing challenge in macroevolutionary research is identifying common drivers of diversification amid the complex interplay of many potentially relevant traits, ecological contexts, and intrinsic characteristics of clades. In this study, we used geometric morphometric and phylogenetic comparative methods to evaluate the tempo and mode of morphological evolution in an adaptive radiation of Malagasy birds, the vangas, and their mainland relatives (Aves: Vangidae). To characterize the morphological diversity of the clade we used both landmarks and semilandmark curves from the bill and neurocranium, and linear measurements of pedal bones, all collected from microCT scans of museum specimens. The Malagasy radiation is more diverse in both skull and foot shape. However, rather than following the classic "early burst" of diversification, trait evolution accelerated well after their arrival in Madagascar, likely driven by the evolution of new modes of foraging and especially of a few species with highly divergent morphologies. Anatomical regions showed differing evolutionary patterns, and the presence of morphological outliers impacted the results of some analyses, particularly of trait integration and modularity. Our results demonstrate that the adaptive radiation of Malagasy vangas has evolved exceptional ecomorphological diversity along multiple, independent trait axes, mainly driven by a late expansion in niche space due to key innovations. Our findings highlight the evolution of extreme forms as an overlooked feature of adaptive radiation warranting further study.