Fossils of
E. vincenti, the
Eocypselus type species (comprising a
wing and pectoral bone) were initially recognized from the
London Clay Formation of England and named by C.J.O. Harrison in 1984. An additional specimen of this species was later identified from the
Fur Formation of Denmark and described in 2010. A second
Eocypselus species,
E. rowei was described in 2013 by Ksepka and colleagues. The collected an exceptionally preserved specimen in the
Green River Formation of Wyoming. The specimen includes well-preserved feathers containing fossilized
melanosomes—pigmentation cell structures—and a nearly complete skeleton. They named the new species in honor of
John Rowe, Chairman of the
Field Museum's Board of Trustees. The discoverers chose to honor Rowe, whom they considered to be a "fossil
geek." In 2024, Mayr and Kitchener described three additional species. The first,
E. geminus (from the Latin
geminus, meaning "twin", due to the specimen's similarity to
E. vincenti) is known from several bones collected in 1991 and 1992 likely belonging to multiple individuals. The second,
E. paulomajor (from the Latin
paulum major, meaning "somewhat larger", as the specimen is slightly larger than
E. vincenti), is known from a partial
furcula and the left
coracoid and
ulna collected in 1997. The third,
E. grandissimus (from the Latin
grandis, since it is the largest
Eocypselus species), is known from several bones collected in 1994. All of the specimens were collected by Michael Daniels from the Walton Member of the London Clay Formation. ==Description==