Editing Molecular clock (section)

===Tip calibration===
Sometimes referred to as [[tip dating]], tip calibration is a method of molecular clock calibration in which fossils are treated as [[taxon|taxa]] and placed on the tips of the tree. This is achieved by creating a matrix that includes a [[molecular phylogenetics|molecular]] dataset for the [[neontology|extant taxa]] along with a [[morphology (biology)|morphological]] dataset for both the extinct and the extant taxa.<ref name="O'Reilly03" /> Unlike node calibration, this method reconstructs the tree topology and places the fossils simultaneously. Molecular and morphological models work together simultaneously, allowing morphology to inform the placement of fossils.<ref name="Donoghue02" /> Tip calibration makes use of all relevant fossil taxa during clock calibration, rather than relying on only the oldest fossil of each clade. This method does not rely on the interpretation of negative evidence to infer maximum clade ages.<ref name="O'Reilly03" />