'Big bang' for tertiary birds?

The early evolution of living birds has been sharply debated, with two disparate interpretations. Molecular-clock studies consistently date the emergence of modern bird orders at similar to 100 million years ago or older, coincidental with major continental breakup. This is supported by some biogeographers who use phylogenetics, accept an ancient evolutionary origin and use historical geology to guide their reasoning. The fossil record, however, provides evidence that modern birds represent an explosive Tertiary radiation, following the Cretaceous-Tertiary cataclysm, and their origins are almost 50 million years younger than that predicted by molecular studies. Here, I argue that this explosive, punctuated model conforms to the typical pattern of vertebrate evolution characterized by rapid diversification following a major extinction event.