The
genus Aquila was introduced by the French zoologist
Mathurin Jacques Brisson in 1760 with the
golden eagle (
Aquila chrysaetos) as the
type species.
Aquila belongs to a close-knit group of "typical" eagles including genera
Hieraaetus,
Lophaetus,
Ictinaetus and Clanga. This group occurs as a clade within the larger group of "booted" eagles (tribe Aquilini or subfamily Aquilinae). The plumage of the more basal members of the booted eagle group, such as
Spizaetus and
Nisaetus, generally has barred underparts in adults, and is distinctly different in juveniles which have plain, pale underparts. In contrast, within the
Aquila–Hieraaetus–Lophaetus clade, adults are generally dark, with juveniles more closely resembling the adults.
Hieraaetus species have both dark and light (or "pied") morphs, with the latter having light, unbarred underparts. Research in molecular genetics found
Aquila and
Hieraaetus to be
polyphyletic. Between 2005 and 2014, the
British Ornithologists' Union included both Bonelli's and the booted eagle in
Aquila. Also, ''
Clements' Checklist merged all Hieraetus
species into Aquila
from 2001 to 2009. The current approach is to keep Hieraaetus'' as a separate genus, with Bonelli's eagle and the African hawk-eagle moved into
Aquila and
Wahlberg's eagle moved into
Hieraaetus. The spotted eagles species, the
greater spotted eagle,
lesser spotted eagle, and
Indian spotted eagle (previously
Aquila clanga,
A. pomarina,
A. (p.) hastata) are thought to be genetically closer to
Ictinaetus and
Lophoaetus than to other
Aquila species, and may be placed in a separate genus,
Clanga. Members of
Aquila (excluding those moved to
Clanga and
Hieraaetus, but including
A. fasciata / spilogaster) share two deletions in the (nuclear) LDH gene, as well as similarities in mitochondrial cyt-B gene sequence, though one of these deletions is reverted in
A. chrysaetos. ==Species==