Skyggedelfin er først beskrevet af [[John Edward Gray]] i 1828, antageligvis på baggrund af et enkelt kranie og konserveret skind sendt fra [[Kap det Gode Håb]] til [[British Museum]] af en kaptajn Haviside. Arten blev først beskrevet under navnet ''Delphinus obscurus''.<ref name=HMM>{{cite book|author=Ridgway, Sam H. |year=|title=Handbook of Marine Mammals: The second book of dolphins and the porpoises, Volume 6 |year=1998 |publisher=Elsevier|pages=85-95|url=http://books.google.com.au/books?id=At4jWmmaq6QC&pg=PA85&dq=Dusky+dolphin&hl=en&ei=792STcTjMcPIcYCjrYkH&sa=X&oi=book_result&ct=result&resnum=8&ved=0CFYQ6AEwBw#v=onepage&q=Dusky%20dolphin&f=false|isbn=0125885067}} </ref>
[[File:Pacific white side dolphin.jpg|thumb|250px|left|The dusky dolphin resembles, and is closely related to, the [[Pacific white-sided dolphin]].]]
However Gray later wrote that a similar dolphin was described as ''Delphinus supercilious'' by French surgeons and naturalists [[René Primevère Lesson]] and Prosper Garnot from a specimen collected off the coast of [[Tasmania]] two years before his own classification.<ref>{{cite journal |last=Gray |first=J. E. |year=1846 |title=On the British Cetacea |journal=The Annuals and Magazine of Natural History |location=London |volume=17 |pages=82–5}}</ref> Gray considered ''D. supercilious'' to be a junior [[Synonym (taxonomy)|synonym]] of his ''D. obscurus'' and gives Lesson and Garnot (1826) credit for their original description. Meanwhile, [[Charles Darwin]] also described what turned out to be this species as ''Delphinus fitzroyi'' from a specimen harpooned off Argentina in 1838. The dusky dolphin was reclassified as ''Prodelphinus obscurus'' in 1885 by British naturalist [[William Henry Flower]],<ref>{{cite book|author=Flower, W. H.|year=1885|title=List of the specimens of Cetacea in the Zoological Department of the British Museum|publisher=British Museum|location= London|pages=28-29|url=http://www.archive.org/stream/listofspecimenso00brituoft#page/28/mode/2up/search/obscurus}} </ref> before gaining its current binomial name, ''Lagenorhynchus obscurus'', from American biologist [[Frederick W. True]] in 1889.<ref>{{cite journal|author=True, F.W.|year=1889|title=Contribution to the natural history of the cetaceans: a review of the family Delphinidae|journal= Bulletin of the U.S. National Museum|volume=36|pages=1-191}}</ref>
===Genetics===
The dusky dolphin and the [[Pacific white-sided dolphin]] are considered [[phylogenetically]] related species. Some researchers have suggested that they are the same species but close scrutiny of morphological and life history parameters does not support this.<ref name= "Perrin"/> The two sister species diverged at around 1.9–3.0 million years ago.<ref name="Pmid">{{cite journal |last1=Cassens |first1=I |last2=Van Waerebeek |first2=K |last3=Best |first3=PB |last4=Tzika |first4=A |last5=Van Helden |first5=AL |last6=Crespo |first6=EA |last7=Milinkovitch |first7=MC |title=Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (''Lagenorhynchus obscurus''). |journal=Molecular ecology |volume=14 |issue=1 |pages=107–21 |year=2005 |pmid=15643955 |doi=10.1111/j.1365-294X.2004.02407.x}}</ref> Recent analysis of the mitochondrial cytochrome b gene indicates that the genus Lagenorhynchus, as traditionally conceived, is not a natural (monophyletic) group.<ref>LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999) "Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences", ''Marine Mammal Science'' 15(3):619–48.</ref> Another study finds that the dusky and the Pacific white-sided dolphin form the [[Sister_taxon#Cladograms|sister group]] to the (expanded) genus ''[[Cephalorhynchus]]''. If this placement is accurate, a new genus name will need to be coined to accommodate these two species.<ref>May-Collado, L., Agnarsson, I. (2006) "Cytochrome b and Bayesian inference of whale phylogeny", ''Molecular Phylogenetics and Evolution'' 38(2):344-54.</ref>
