Macro- and micro-evolution of avian bills

Bill shape in birds is closely associated with diet and foraging techniques and is known to have a key role in avian adaptive radiations. Darwin’s finches of the Galapagos Islands are a good example of bill variation at a microevolutionary scale, within a limited geographical area and over a comparatively short period. But how has avian bill shape evolved across time to attain its outstanding current diversity? Three-dimensional scans of museum study skins, comprising over 2,000 species and over 97% of extant genera, give interesting results that support the well-known model of the paleontologist George Gaylord Simpson#R. The rise of modern birds from the late Cretaceous onwards apparently occurred in a rapidly changing world, coinciding with extensive ecological opportunity. This may have driven Simpsonian mega-evolution across adaptive zones, later giving way to smaller scale fine-tuning of the bill as avian diversity expanded across the globe. Insular adaptive radiations in passerine birds, for example in Malagasy vangas, Hawaiian honeycreepers and the aforementioned Galapagos finches, have provided some of the fastest rates of bill evolution, closely linked to ecological opportunity, suggesting that lineages radiating on isolated island archipelagos can explore morphological space independently of the global avifauna.