Molecular clocks can provide insights into the evolutionary timescale of groups with unusually biased or fragmentary fossil records, such as birds. In those cases, it is advantageous to establish internal anchor points—molecular time estimates—using the best external fossil calibrations. In turn, those anchor points can be used as calibrations for more detailed time estimation within the group under study. This method also avoids the inherent problems in drawing conclusions about the evolution of a group based on data tied to the poor fossil record of that same group. The galliform-anseriform divergence (∼90 million years ago) is an example of such an ideal anchor point for molecular clock analyses in birds.
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