Editing Forelimb (section)

=== Flippers ===
Marine mammals have evolved several times. Over the course of their evolution, they develop streamlined hydrodynamic bodies. The forelimb thus develops into a [[Flipper (anatomy)|flipper]]. The forelimbs of cetaceans, pinnipeds, and sirenians presents a classic example of convergent evolution. There is widespread convergence at the gene level.<ref>{{Cite journal|last1=Chikina|first1=Maria|last2=Robinson|first2=Joseph D.|last3=Clark|first3=Nathan L.|date=2016-09-01|title=Hundreds of Genes Experienced Convergent Shifts in Selective Pressure in Marine Mammals|url= |journal=Molecular Biology and Evolution|language=en|volume=33|issue=9|pages=2182–2192|doi=10.1093/molbev/msw112|pmid=27329977|pmc=5854031|issn=0737-4038}}</ref> Distinct substitutions in common genes created various aquatic adaptations, most of which constitute [[parallel evolution]] because the substitutions in question are not unique to those animals.<ref name=":3">{{Cite journal|last1=Zhou|first1=Xuming|last2=Seim|first2=Inge|last3=Gladyshev|first3=Vadim N.|date=2015-11-09|title=Convergent evolution of marine mammals is associated with distinct substitutions in common genes|journal=Scientific Reports|language=en|volume=5|issue=1|pages=16550|doi=10.1038/srep16550|pmid=26549748|pmc=4637874|issn=2045-2322|bibcode=2015NatSR...516550Z|doi-access=free}}</ref>

When comparing cetaceans to pinnipeds to sirenians, 133 parallel amino acid substitutions occur. Comparing and contrasting cetaceans-pinnipeds, cetaceans-sirenians, and pinnipeds-sirenians, 2,351, 7,684, and 2,579 substitutions occur, respectively.<ref name=":3" />