Caprimulgiformes
Encyclopedia
The Caprimulgiformes is an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s that includes a number of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s with global distribution (except Antarctica). They are generally insectivorous
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....

 and nocturnal
Nocturnal animal
Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. The common adjective is "nocturnal"....

. The order gets its name from the Latin for "goat-sucker", an old name based on an erroneous view of the European Nightjar
European Nightjar
The European Nightjar, or just Nightjar, Caprimulgus europaeus, is the only representative of the nightjar family of birds in most of Europe and temperate Asia.- Habitat and distribution :...

's feeding habits.

Systematics

The classification of the various birds that make up the order has long been controversial and difficult, particularly in the case of the nightjars. All things considered, the nightjar order would probably best be limited to potoos, nightjars, and eared-nightjars, all other lineages being elevated to order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 level, and the owlet-nightjar
Owlet-nightjar
Owlet-nightjars are small nocturnal birds related to the nightjars and frogmouths. Most are native to New Guinea, but some species extend to Australia, the Moluccas, and New Caledonia. A New Zealand species is extinct...

s being altogether distant:
  • Family Steatornithidae (Oilbird
    Oilbird
    The Oilbird , also known as Guácharo, is a bird found in the northern areas of South America . They are nocturnal feeders on the fruits of the Oil Palm and tropical laurels, and are the only nocturnal fruit eating birds in the world...

    ) - probably distinct order N.N. ("Steatornithiformes")
  • Family Podargidae (frogmouth
    Frogmouth
    The frogmouths are a group of nocturnal birds related to the nightjars. They are found from India across southern Asia to Australia.They are named for their large flattened hooked bills and huge frog-like gape, which they use to capture insects. Their flight is weak.They rest horizontally on...

    s, 15 species in 3 genera) - probably distinct order Podargiformes

  • Family Nyctibiidae (Potoos, about 5 species in 1 genus)
  • Family Caprimulgidae
    • Subfamily Chordeilinae (New World nighthawks)
    • Subfamily Caprimulginae (typical nightjars)
  • Family Eurostopodidae
    Eurostopodidae
    The Eared nightjars are a small family of nocturnal birds related to nightjars, although the taxonomy is uncertain. There are seven species, mainly found in forest and scrub from China to Australia. All are placed in one genus, Eurostopodus. They are long winged birds with plumage patterned with...

     (eared nightjars)


Traditionally, they were regarded, on morphological grounds, as being midway between the owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...

s (Strigiformes) and the swift
Swift
The swifts are a family, Apodidae, of highly aerial birds. They are superficially similar to swallows, but are actually not closely related to passerine species at all; swifts are in the separate order Apodiformes, which they share with hummingbirds...

s. Like the owls, they are nocturnal hunters with a highly developed sense of sight, and like the swifts they are excellent flyers with small, weak legs. At one time or another, they have been allied with owls, swifts, kingfisher
Kingfisher
Kingfishers are a group of small to medium sized brightly coloured birds in the order Coraciiformes. They have a cosmopolitan distribution, with most species being found in the Old World and Australia...

s, hoopoe
Hoopoe
The Hoopoe is a colourful bird that is found across Afro-Eurasia, notable for its distinctive 'crown' of feathers. It is the only extant species in the family Upupidae. One insular species, the Giant Hoopoe of Saint Helena, is extinct, and the Madagascar subspecies of the Hoopoe is sometimes...

s, mousebird
Mousebird
The mousebirds are a small group of birds which have no known close affinities to other groups, though they and the parrots and cockatoos may be closer to each other than to other birds. The mousebirds are therefore given order status as Coliiformes...

s, hornbill
Hornbill
Hornbills are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. They are characterized by a long, down-curved bill which is frequently brightly-colored and sometimes has a casque on the upper mandible. Both the common English and the scientific name of the family...

s, roller
Roller
The rollers are an Old World family, Coraciidae, of near passerine birds. The group gets its name from the aerial acrobatics some of these birds perform during courtship or territorial flights. Rollers resemble crows in size and build, and share the colourful appearance of kingfishers and...

s, bee-eater
Bee-eater
The bee-eaters are a group of near-passerine birds in the family Meropidae. Most species are found in Africa and Asia but others occur in southern Europe, Australia, and New Guinea. They are characterised by richly coloured plumage, slender bodies, and usually elongated central tail feathers...

s, woodpecker
Woodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....

s, trogon
Trogon
The trogons and quetzals are birds in the order Trogoniformes which contains only one family, the Trogonidae. The family contains 39 species in eight genera. The fossil record of the trogons dates back 49 million years to the mid-Eocene. They might constitute a member of the basal radiation of...

s and hummingbirds.

Based on analysis of sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

 data - notably β-fibrinogen
Fibrinogen
Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...

 intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...

 7 -, Fain & Houde (2004) considered the families of the Caprimulgiformes to be members of the proposed clade Metaves, which also includes the hoatzin
Hoatzin
The Hoatzin , also known as the Hoactzin, Stinkbird, or Canje Pheasant, is a species of tropical bird found in swamps, riverine forest and mangrove of the Amazon and the Orinoco delta in South America...

, tropicbirds, sandgrouse
Sandgrouse
The sandgrouse are a family, Pteroclididae, of 16 bird species, the only living members of the order Pteroclidiformes. They are restricted to treeless open country in the Old World, such as plains and semi-deserts. They are distributed across northern, southern and eastern Africa as well as...

, pigeons, kagu
Kagu
The Kagu or Cagou is a crested, long-legged, and bluish-grey bird endemic to the dense mountain forests of New Caledonia. It is the only surviving member of the genus Rhynochetos and the family Rhynochetidae, although a second species has been described from the fossil record...

, sunbittern
Sunbittern
The Sunbittern, Eurypyga helias is a bittern-like bird of tropical regions of the Americas, and the sole member of the family Eurypygidae and genus Eurypyga.-Description and reproduction:...

, mesites, flamingos, grebes and swifts and hummingbirds. This clade was also found by the expanded study of Ericson et al. (2006), but support was extremely weak.

While only the latter study recovered monophyly of the Cypselomorphae
Cypselomorphae
Cypselomorphae is a clade of birds. It includes the living families and orders Caprimulgidae , Nyctibiidae , Apodiformes , as well as the Aegotheliformes whose distinctness was only recently realized...

 (see below) within Metaves, the former was based on only a single locus and could not resolve their relationships according to standard criteria of statistical confidence. No morphological synapomorphies have been found that uniquely unite Metaves (or Caprimulgiformes for that matter), but numerous unlinked nuclear genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

 independently support their monophyly either in majority or whole. Ericson et al. (2006) concluded that if valid, the "Metaves" must originate quite some time before the Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

, and they reconciled this with the fossil record.

While the relationships of cypselomorphs are a subject of ongoing debate, the phylogeny of the individual lineages is better resolved. Much of the remaining uncertainty regards minor details.

Initial mtDNA cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...

 sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

 analysis (Mariaux & Braun 1996) agreed with earlier morphological (Cracraft 1981) and DNA-DNA hybridization (Sibley & Ahlquist 1990) studies insofar as that the oilbird and the frogmouths seemed rather distinct. The other lineages appeared to form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

, but this is now known to have been caused by methodological limitiations.

The Aegothelidae (owlet-nightjar
Owlet-nightjar
Owlet-nightjars are small nocturnal birds related to the nightjars and frogmouths. Most are native to New Guinea, but some species extend to Australia, the Moluccas, and New Caledonia. A New Zealand species is extinct...

s) with about a dozen living species in one genus are apparently closer to the Apodiformes
Apodiformes
Traditionally, the bird order Apodiformes contained three living families: the swifts , the tree swifts , and the hummingbirds . In the Sibley-Ahlquist taxonomy, this order is raised to a superorder Apodimorphae in which hummingbirds are separated as a new order, Trochiliformes...

 (Mayr 2002); these and the Caprimulgiformes are closely related, being grouped together as Cypselomorphae
Cypselomorphae
Cypselomorphae is a clade of birds. It includes the living families and orders Caprimulgidae , Nyctibiidae , Apodiformes , as well as the Aegotheliformes whose distinctness was only recently realized...

. The oilbird and the frogmouths seem quite distinct among the remaining Caprimulgiformes, but their exact placement cannot be resolved based on osteological data alone (Mary 2002).

Even the study of Ericson et al. could not properly resolve the oilbird's and frogmouths' relationships beyond the fact that they are quite certainly well distinct. It robustly supported, however, the idea that the owlet-nightjars should be considered closer to Caprimulgiformes, unlike the methodologically weaker studies of Mariaux & Braun (1996) and Fain & Houde (2004).

Alternatively, Mayr's phylogenetic taxon Cypselomorphae might be placed at order rank and substitute the two present orders Caprimulgiformes and Apodiformes. Such a group would be fairly uninformative as regards its evolutionary history, as it has to include some very plesiomorphic and some extremely derived lineages (such as hummingbirds) to achieve monophyly.

Evolution

The fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 record of caprimulgiform birds (in the loose sense) is rather scant. Nonetheless, it supports the emerging consensus phylogeny well. The genus Paraprefica, probably from the Early Eocene (though this is somewhat uncertain), seems to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 form that at times has been allied with the oilbird and the potoos, but cannot be assigned to either with certainty. In the consensus scenario, it would represent a record of the initial divergence of the three lineages.

This nicely agrees with fossils suggesting that the basal divergence of the owlet-nightjar and apodiform branch also occurred during that time. In addition, Eocypselus, a Late Paleocene or Early Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 genus of north-central Europe, cannot be assigned to any one cypselomorph lineage with certainty but appears to be some ancestral form.

These Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

 birds strongly suggest that the two main extant lineages of cypselomorphs separated about 60-55 mya (Selandian
Selandian
The Selandian is in the geologic timescale an age or stage in the Paleocene. It spans the time between and . It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "Middle Paleocene".-Stratigraphic...

-Thanetian
Thanetian
The Thanetian is, in the ICS' Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between and . The Thanetian is preceded by the Selandian age and followed by the Ypresian age...

), and that some time around the Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...

-Bartonian
Bartonian
The Bartonian is, in the ICS's geological timescale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between and . It is preceded by the Lutetian and is followed by the Priabonian age.-Stratigraphic definition:...

boundary, some 40 mya, the common ancestors of Nyctibiidae, Caprimulgidae and Eurostopodidae diverged from those of oilbird and frogmouths.
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