Page "Parallel evolution" Paragraph 4

When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective.

For instance, the striking example of similar placental and marsupial forms is described by Richard Dawkins in The Blind Watchmaker as a case of convergent evolution, because mammals on each continent had a long evolutionary history prior to the extinction of the dinosaurs under which to accumulate relevant differences.

Stephen Jay Gould describes many of the same examples as parallel evolution starting from the common ancestor of all marsupials and placentals.

Many evolved similarities can be described in concept as parallel evolution from a remote ancestor, with the exception of those where quite different structures are co-opted to a similar function.

For example, consider Mixotricha paradoxa, an eukaryotic microbe which has assembled a system of rows of apparent cilia and basal bodies closely resembling that of ciliates but which are actually smaller symbiont microorganisms, or the differently oriented tails of fish and whales.

Conversely, any case in which lineages do not evolve together at the same time in the same ecospace might be described as convergent evolution at some point in time.