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, long before the final extinction of the dinosaurs. These molecular dates have been used to challenge the idea that the ordinal diversification of mammals was triggered by the availability of 'empty niches' left vacant by the disappearance of the dinosaurs. However, the broad discrepancies between molecular date estimates from different studies warn that molecular dates should not be accepted uncritically. Consideration of the wide confidence intervals around molecular date estimates, and the potential for geographic bias in the fossil record, could lessen the discrepancy between molecular and palaeontological data but might still prompt a re-evaluation of the timing and causes of the mammalian radiation.