Rates of passerine body plan evolution in time and space

The rates and patterns of phenotypic evolution are known to vary dramatically across time and space, yet the drivers of this variation remain poorly understood. Using over 170,000 skeletal measurements across 2,057 species of Passeriformes-the most diverse order of living birds-we reconstruct the evolutionary history of passerine body plan diversification over the past ~50 Myr. We find that the history of passerine body plan evolution is dominated by rare, hierarchically nested bursts of phenotypic innovation near the origins of major taxonomic groups, indicating that such radiations have played a disproportionately large role in shaping global passerine diversity. These bursts are temporally aligned with intervals of increased climatic instability in Earth's history and are reflected in contemporary latitudinal gradients, where assemblages at higher latitudes host species with elevated mean rates of phenotypic evolution and more modular trait covariation. Together, our findings support the hypothesis that climatic variability may act as a recurring driver of phenotypic diversification, linking deep-time pulses of innovation to broad-scale spatial patterns in evolutionary tempo.