Growing up with dinosaurs: molecular dates and the mammalian radiation

Dates of divergence derived from molecular data have been used to place the beginning of the radiation of modern mammalian orders in the Cretaceous, l ong before the final extinction of the dinosaurs. These molecular dates hav e been used to challenge the idea that the ordinal diversification of mamma ls was triggered by the availability of 'empty niches' left vacant by the d isappearance of the dinosaurs. However, the broad discrepancies between mol ecular date estimates from different studies warn that molecular dates shou ld not be accepted uncritically. Consideration of the wide confidence inter vals around molecular date estimates, and the potential for geographic bias in the fossil record, could lessen the discrepancy between molecular and p alaeontological data but might still prompt a reevaluation of the timing an d causes of the mammalian radiation.