''Eocypselus'' is a genus of prehistoric birds related to modern

hummingbird Hummingbirds are birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With approximately 366 species and 113 genus, genera, they occur from Alaska to Tierra del Fuego, but most species are found in Cen ...

s and

swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIF ...

s. Five species of ''Eocypselus'' are currently known. Compared with modern apodiforms, it may have been a better percher with shorter wing feathers, and it might have been nocturnal.

Discovery and naming

Fossils of ''E. vincenti'', the ''Eocypselus''

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

(comprising a

wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...

and pectoral bone) were initially recognized from the

London Clay Formation The London Clay Formation is a marine geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from the ...

of England and named by C.J.O. Harrison in 1984. An additional specimen of this species was later identified from the

Fur Formation The Fur Formation is a marine geological formation of Ypresian ( Lower Eocene Epoch, c. 56.0-54.5 Ma) age which crops out in the Limfjord region of northern Denmark from Silstrup via Mors and Fur to Ertebølle, and can be seen in many cliffs and ...

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 The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River (Colorado River), Green River in Colorado, Wyoming, and Utah. The sedimen ...

of Wyoming. The specimen includes well-preserved feathers containing fossilized

melanosome A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotectio ...

s—pigmentation cell structures—and a nearly complete skeleton. They named the new species in honor of John Rowe, Chairman of the

Field Museum The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educationa ...

's Board of Trustees. The discoverers chose to honor Rowe, whom they considered to be a "fossil

geek The word ''geek'' is a slang term originally used to describe Eccentricity (behavior), eccentric or non-mainstream people; in current use, the word typically connotes an expert or enthusiast obsessed with a hobby or intellectual pursuit. In th ...

." 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 The (Latin for "little fork"; : furculae) or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is either an interclavicle or formed by the fusion of the two clavicles. In birds, its primary function is ...

and the left

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

and

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

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

''Eocypselus'' shares features in common with both hummingbirds and swifts, leading Ksepka to declare that it "represents the closest we've gotten to the point where swifts and hummingbirds went their separate ways". It was probably not a hoverer, like a hummingbird, but also not a fast flyer like a swift. ''E. rowei'' was less than from head to tail. Its feathers made up more than half the size of its wingspan. The bird was small enough to fit into the palm of a hand and weighed less than . It probably had black plumage and may have had an iridescent sheen, like modern swifts.

Classification

''Eocypselus'' is a basal form of the order

Apodiformes The Apodiformes is an Order (biology), order, or Taxonomy, taxonomic grouping, of Bird, birds which traditionally contained three living Family (biology), families—the Swift (bird), Apodidae (swifts), the Treeswift, Hemiprocnidae (treeswifts), ...

, which traditionally includes

tree swift Treeswifts or crested swifts are a family, the Hemiprocnidae, of aerial near passerine birds, closely related to the true swifts. The family contains a single genus, ''Hemiprocne'', with four species. They are distributed from India and Southeast ...

s, and

s.Mayr, G. (2004)
Phylogeny of early Tertiary swifts and hummingbirds (Aves: Apodiformes)
Auk, 120 (1): 145-151.

References

{{Taxonbar, from=Q21078744 Apodiformes Prehistoric bird genera Fossil taxa described in 1984 Birds described in 1984 Prehistoric birds of Europe Fossils of Denmark Eocene birds of Europe

Discovery and naming

Description

Classification

See also

References