Editing Apodiformes (section)

==Evolution==
The Apodiformes evolved in the Northern Hemisphere. ''[[Eocypselus]]'', a primitive genus known from the Late [[Paleocene]] or Early [[Eocene]] of north-central Europe, is somewhat difficult to assign; it is considered a primitive hemiprocnid.<ref>{{cite journal |last1=Dyke |first1=Gareth J. |last2=Waterhouse |first2 = David M. |last3=Kristoffersen |first3=Anette M. |name-list-style=amp |date=October 2004 |title=Three new fossil landbirds from the early Paleogene of Denmark |journal=Bulletin of the Geological Society of Denmark |volume=51 |issue=1 |pages=77–85 |doi=10.37570/bgsd-2004-51-06 |url=https://2dgf.dk/xpdf/bull51-1-77-85.pdf}}</ref>  This would suggest that the major apodiform lineages diverged shortly after the [[Cretaceous–Paleogene boundary]]. However, the perching adaptation of the foot of ''Eocypselus'' on which this theory rests may just as well be a [[symplesiomorphy]].
Most researchers believe that presently this genus cannot be unequivocally assigned to either the Apodiformes or the Caprimulgiformes. 

The Early Eocene ''[[Primapus]]'', found in England, is similar to both a primitive swift and the [[aegialornithidae|aegialornithids]], which are in some aspects intermediate between swifts and owlet-nightjars. Fossil evidence demonstrates the existence of swifts during that period in [[Europe]]. At that time, most of Europe had a humid, subtropical climate, possibly comparable to modern-day southern China. For a map of Early–Middle Eocene Earth, see the Paleomap project;<ref>{{cite web |url=http://www.scotese.com/newpage9.htm |title=During the Early Cenozoic India began to Collide with Asia |author=Christopher R. Scotese  |publisher=Paleomap project  |access-date=20 September 2010}}</ref> here note that both the [[Caucasus Mountains]] and the [[Alps]] did not exist yet and aegialornithids were possibly present in North America.<ref>Somewhat doubtful, as this is difficult to reconcile with the other aegialornithid fossils and ''Primapus''.</ref>
By the late Eocene (around 35 [[mya (unit)|MYA]]), primitive hummingbirds started to diverge from the related jungornithids; the Middle Eocene ''[[Parargornis]]'' ([[Messel pit|Messel]], Germany) and the Late Eocene ''[[Argornis]]'', found in today's southernmost [[Russia]], belong to this lineage. ''[[Cypselavus]]'' (Late Eocene – Early Oligocene of Quercy, France)<!-- Auk120:145 --> was either a primitive hemiprocnid or an aegialornithid.

The placement of the Aegialornithidae is not quite clear. Various analyses place them sufficiently close to the Apodiformes to be included here, or into the unique owlet-nightjar lineage in the Cypselomorphae.