Editing Transitional fossil (section)

===Transitional versus ancestral===
A source of confusion is the notion that a transitional form between two different taxonomic groups must be a direct ancestor of one or both groups. The difficulty is exacerbated by the fact that one of the goals of evolutionary taxonomy is to identify taxa that were ancestors of other taxa. However, because evolution is a branching process that produces a complex bush pattern of related [[species]] rather than a linear process producing a ladder-like progression, and because of the incompleteness of the fossil record, it is unlikely that any particular form represented in the fossil record is a direct ancestor of any other. Cladistics deemphasizes the concept of one taxonomic group being an ancestor of another, and instead emphasizes the identification of sister taxa that share a more recent common ancestor with one another than they do with other groups. There are a few exceptional cases, such as some marine [[plankton]] [[Micropaleontology|microfossil]]s, where the fossil record is complete enough to suggest with confidence that certain fossils represent a population that was actually ancestral to a later population of a different species.<ref>{{cite journal |last1=Prothero |first1=Donald R. |last2=Lazarus |first2=David B. |date=June 1980 |title=Planktonic Microfossils and the Recognition of Ancestors |journal=[[Systematic Biology]] |volume=29 |issue=2 |pages=119–129 |doi=10.1093/sysbio/29.2.119 |issn=1063-5157 }}</ref> But, in general, transitional fossils are considered to have features that illustrate the transitional anatomical features of actual common ancestors of different taxa, rather than to ''be'' actual ancestors.<ref name=Prothero>{{harvnb|Prothero|2007|pp=133–135}}</ref>