Editing Molecular clock (section)

===Total evidence dating===
This approach to tip calibration goes a step further by simultaneously estimating fossil placement, topology, and the evolutionary timescale. In this method, the age of a fossil can inform its phylogenetic position in addition to morphology. By allowing all aspects of tree reconstruction to occur simultaneously, the risk of biased results is decreased.<ref name="Donoghue02" /> This approach has been improved upon by pairing it with different models. One current method of molecular clock calibration is total evidence dating paired with the fossilized birth-death (FBD) model and a model of morphological evolution.<ref name=Heath05>{{cite journal | vauthors = Heath TA, Huelsenbeck JP, Stadler T | title = The fossilized birth-death process for coherent calibration of divergence-time estimates | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 111 | issue = 29 | pages = E2957–E2966 | date = July 2014 | pmid = 25009181 | pmc = 4115571 | doi = 10.1073/pnas.1319091111 | name-list-style = amp | arxiv = 1310.2968 | doi-access = free | bibcode = 2014PNAS..111E2957H }}</ref> The FBD model is novel in that it allows for "sampled ancestors", which are fossil taxa that are the direct ancestor of a living taxon or [[lineage (evolution)|lineage]]. This allows fossils to be placed on a branch above an extant organism, rather than being confined to the tips.<ref name=Gavryushkina06>{{cite journal | vauthors = Gavryushkina A, Heath TA, Ksepka DT, Stadler T, Welch D, Drummond AJ | title = Bayesian Total-Evidence Dating Reveals the Recent Crown Radiation of Penguins | journal = Systematic Biology | volume = 66 | issue = 1 | pages = 57–73 | date = January 2017 | pmid = 28173531 | pmc = 5410945 | doi = 10.1093/sysbio/syw060 | name-list-style = amp | arxiv = 1506.04797 }}</ref>