Rates of ecomorphological trait evolution in passerine birds are independent of clade age

While the links between species richness and diversification rates with clade age have been studied extensively, very few studies have investigated the relationship between the rates of trait evolution and clade age. It is therefore not well understood whether the rate of morphological trait evolution within a clade is similar or dissimilar in clades of different ages. We compare the relationship between the rates of trait evolution and clade age across eight monophyletic clades of passerine birds by investigating ecomorphological traits, i.e. morphological traits that are of high ecological importance. We study the ecomorphological divergence pattern using disparity through time analyses and then determine the best-fitting model of evolution for each trait in each clade. We find no support for a dependence of evolutionary rates on clade age, and further show that Early Burst models of trait evolution are rarely the best fitting models within these clades. Our results reveal the unpredictability of ecomorphological trait evolution despite commonly suggested evolutionary patterns of key innovations or adaptive radiations.