70 (4): 571 – 585
2020© Senckenberg Gesellschaft für Naturforschung, 2020.

Phylogenetic definitions for Caprimulgimorphae (Aves)and major constituent clades under the International
Code of Phylogenetic Nomenclature
Albert Chen 1, 2, * & Daniel J. Field 2, **Milner Centre for Evolution, University of Bath, Claverton Down, Bath, United Kingdom BA2 7AY — 2 Department of Earth Sciences, University of Cambridge, Downing St, Cambridge, United Kingdom CB2 3EQ — * Corresponding author; ac2318@cam.ac.uk — ** Corresponding
author; djf70@cam.ac.uk
1

Submitted July 10, 2020.
Accepted September 21, 2020.
Published online at www.senckenberg.de/vertebrate-zoology on October 21, 2020.
Published in print Q4/2020.
Editor in charge: Martin Päckert

Abstract
Phylogenetic nomenclature, a system of taxonomic nomenclature in which taxon names are defined based on phylogenetic relationships,
has been widely adopted in recent decades, particularly by vertebrate palaeontologists. However, formal regulation of this taxonomic system had been non-existent until the recent implementation of the International Code of Phylogenetic Nomenclature (PhyloCode). To fulfil
the requirements of the PhyloCode, we explicitly establish phylogenetic definitions that we recommended in a recent phylogenetic study
on the avian taxon Caprimulgimorphae (which includes nightjars, potoos, frogmouths, swifts, hummingbirds, and others) and many of its
major constituent subclades. Two new names are coined: Sedentaves (for the smallest crown clade uniting Steatornis and Nyctibiidae) andLetornithes (for the smallest crown clade uniting Podargidae and Daedalornithes). We also briefly review the fossil record and diagnostic
morphological apomorphies of caprimulgimorph clades for which relevant information is available.

Key words
Caprimulgiformes, nomenclature, phylogeny, Strisores, taxonomy.

Introduction
Phylogenetic nomenclature is a system of taxonomic
nomenclature in which taxon names are defined basedon the phylogenetic relationships among organisms (deQueiroz & Gauthier, 1990). Although the basic tenetsof phylogenetic nomenclature have been widely adopted,
particularly by vertebrate palaeontologists (e.g., Sereno,
1998; Clarke, 2004; Joyce et al., 2004; Nesbitt, 2011;
O’Leary et al., 2013; Hendrickx et al., 2015; Ezcurra,
2016; Chen et al., 2019; Field et al., 2020), the establishment of taxon names and their associated definitions under this taxonomic system had not been formally regulated until recently. As of June 2020, the International Codeof Phylogenetic Nomenclature (PhyloCode) (de Queiroz& Cantino, 2020) has gone into effect with the publication of the companion volume Phylonyms: A Companion

to the PhyloCode (de Queiroz et al., 2020) and the registration database RegNum (Cellinese & Dell, 2020), thus
providing a long-awaited framework of formal rules andguidelines for phylogenetic nomenclature. Per PhyloCo­de Recommendation 6.1A, all technical taxon names will
be italicized in the present contribution.
Under PhyloCode Article 7.1, phylogenetic definitions
recommended prior to the publication of Phylonyms are
not considered established. To be formally recognized,
all previously suggested phylogenetic definitions must be
re-established in a subsequent publication fulfilling the requirements outlined by the PhyloCode. A recent paper weco-authored (Chen et al., 2019) proposed the first explicit
phylogenetic definitions for many of the higher-order taxon names within Caprimulgimorphae (including the crown

ISSN 1864-5755 | eISSN 2625-8498 | DOI: 10.26049/VZ70-4-2020-03

571

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent cladesFig. 1. Phylogenetically defined names for Caprimulgimorphae shown on the best-supported topology for this clade from Chen et al.
(2019). All definitions follow those proposed in the present contribution, except for Daedalornithes and Apodiformes, which follow Sangster (2020a, b), and Pan-Trochilidae and Trochilidae, which follow McGuire et al. (2009). Closed circles at nodes denote node-based
names for crown clades (associated names written in blue to the right of the relevant node), and open semi-circles denote branch-based
names for the total clade comprising that branch and the crown clade it subtends (associated names written in red to the left of the relevant
semi-circle). Triangles with numbers represent extant crown clade diversity of terminal taxa, with the number of extant species following
version 1 of Birds of the World (Billerman et al., 2020). The steatornithiform crown clade contains only Steatornis caripensis. The names
Podargocypseli, Cypselomorphae, and Caprimulgi are defined in the main text, but are not applicable to this tree; conversely, some of thenames shown here may not be applicable to other topologies. All photos © Daniel J. Field; photographed species (L–R) are Chordeiles
minor (Caprimulgidae), Steatornis caripensis, Nyctibius griseus (Nyctibiidae), Podargus strigoides (Podargidae), Aegotheles cristatus,
Hemiprocne comata, Apus apus (Apodidae), and Selasphorus platycercus (Trochilidae).

clade Strisores), an avian clade that has been the subject ofnumerous other phylogenetic studies (Mayr, 2002, 2010a;
Braun & Huddleston, 2009; Nesbitt et al., 2011; Ksepka
et al., 2013; White & Braun, 2019). As the first and only
authors to explicitly suggest phylogenetic definitions formost of these clade names, in this manuscript we aim toformalize these definitions, restated or modified from Chenet al. (2019) following the rules of the PhyloCode. In addition, diagnostic morphological apomorphies are reviewed
for select clades that have been adequately sampled andcharacterized in morphological studies.
Chen et al. (2019) also proposed or listed phylogenetic definitions for the caprimulgimorph clades Daeda­
lornithes and Apodiformes; however, those names havealready been defined following PhyloCode requirements
by Sangster (2020a, b), so they will not be covered here.
A graphical representation of our recommended taxonomic scheme is shown in Fig. 1.

Phylogenetic nomenclature
As in Chen et al. (2019), we have elected to define several names for hypothesized clades that have not been recovered by the most recent phylogenetic analyses, name572

ly Podargocypseli, Cypselomorphae, and Caprimulgi.
Although we recognize that the balance of available evidence does not support the monophyly of these groups,
we do not exclude the possibility that future research
may revive support for at least some of them, given thatthe interrelationships within Caprimulgimorphae have
proven challenging to disentangle definitively. Defining
Podargocypseli, Cypselomorphae, and Caprimulgi here
ensures that phylogenetically defined names are available for these hypothetical clades if they gain newfoundsupport in the future, and also facilitates discussion about
historical hypotheses of caprimulgimorph phylogeny.

Caprimulgimorphae Cracraft, 2013
[Chen & Field], converted clade nameRegistration number. 383
Definition. The total clade containing Caprimulgus eu­ro­paeus Linnaeus, 1758 (Caprimulgidae), Steatornis ca­ri­
pen­sis Humboldt, 1817 (Steatornithidae), Nyctibius (ori­gi­nally Caprimulgus) grandis (Gmelin, 1789) (Nyctibi­idae), Podargus (originally Caprimulgus) strigoides (La­tham, 1801) (Podargidae), Aegotheles (originally Ca­pri­

VERTEBRATE ZOOLOGY — 70 (4) 2020

mul­gus) cristatus (Shaw in White, 1790) (Aegothelidae),and Apus (originally Hirundo) apus (Linnaeus, 1758)(Apodi­for­mes) but not Phoenicopterus ruber Linnaeus,
1758 (Mi­ran­dor­ni­thes or Phoenicopterimorphae), Co­
lum­­ba oenas Linnaeus, 1758 (Columbimorphae), Otis
tar­da Linnaeus, 1758 (Otidimorphae), Musophaga (ori­gi­nal­ly Tauraco) violacea (Isert, 1788) (Otidimorphae),Opi­stho­co­mus (originally Phasianus) hoazin (Statius Mül­­ler, 1776) (Opisthocomiformes), Grus (originally Ar­dea)
grus (Linnaeus, 1758) (Gruiformes), Charadrius hia­­ti­cu­
la Linnaeus, 1758 (Charadriiformes), Phaethon ae­the­­reus Linnaeus, 1758 (Phaethontimorphae), Pro­cel­la­ria
aequinoctialis Linnaeus, 1758 (Aequornithes), and Vul­tur
gryphus Linnaeus, 1758 (Telluraves). This is a total-­clade
definition.
Abbreviated definition. Total ∇ (Caprimulgus euro­
paeus Linnaeus, 1758 & Steatornis caripensis Humboldt,
1817 & Nyctibius grandis (Gmelin, 1789) & Podargus
strigoides (Latham, 1801) & Aegotheles cristatus (Shaw,
1790) & Apus apus (Linnaeus, 1758) ~ Phoenicopterus
ruber Linnaeus, 1758 & Columba oenas Linnaeus, 1758
& Otis tarda Linnaeus, 1758 & Musophaga violacea (Isert, 1788) & Opisthocomus hoazin (Statius Müller, 1776)& Grus grus (Linnaeus, 1758) & Charadrius hiaticula
Linnaeus, 1758 & Phaethon aethereus Linnaeus, 1758
& Procellaria aequinoctialis Linnaeus, 1758 & Vultur
gryphus Linnaeus, 1758).
Reference phylogeny. Figure 1 in Prum et al. (2015)
should be considered the primary reference phylogeny.
Figure 1 in Jarvis et al. (2014) and Figure 3 in Reddy
et al. (2017) may be regarded as secondary reference
phylogenies.
Composition. Caprimulgimorphae includes Strisores
and all extinct taxa more closely related to Strisores thanto any other extant taxon. At present, no definitive members of Caprimulgimorphae outside of Strisores havebeen identified in the fossil record.
Comments. Cracraft (2013) coined Caprimulgimor­
phae as an alternative to Strisores (see comments on
Strisores) to provide a name with a suitable suffix tobe ranked at the level of superorder. Correspondence
between assigned rank and name formulation is not ofconcern under the PhyloCode (Article 3.1) beyond theencouragement of definitions consistent with a nested hierarchy that specific prefixes or suffixes imply (Recommendation 11G). Chen et al. (2019) suggested the use of
Caprimulgimorphae for total-group Strisores, allowing
both names to retain utility in rank-based classifications.
As Caprimulgimorphae is the only pre-existing namethat has been proposed for the total group of Strisores,
we follow this definition here.
Given that the precise interrelationships among the
major clades of neoavian birds remain unsettled, we
employ multiple external specifiers representing major
neoavian groups recovered as monophyletic by mostrecent phylogenomic studies (Jarvis et al., 2014; Prumet al., 2015; Reddy et al., 2017; Kimball et al., 2019;
Kuhl et al., 2020).

Strisores Cabanis, 1847 [Chen & Field],converted clade nameRegistration number. 384
Definition. The smallest crown clade containing Capri­
mulgus europaeus Linnaeus, 1758 (Caprimulgiformes),
Steatornis caripensis Humboldt, 1817 (Steatornithifor­mes), Nyctibius (originally Caprimulgus) grandis (Gme­lin, 1789) (Nyctibiiformes), Podargus (originally Ca­pri­mul­gus) strigoides (Latham, 1801) (Podargiformes), Ae­
gotheles (originally Caprimulgus) cristatus (Shaw, 1790)(Aegotheliformes), and Apus (originally Hirundo) apus
(Linnaeus, 1758)  (Apodiformes).  This  is  a  minimumcrown-clade definition.
Abbreviated definition. Min crown ∇ (Caprimulgus eu­
ropaeus Linnaeus, 1758 & Steatornis caripensis Humboldt, 1817 & Nyctibius grandis (Gmelin, 1789) & Po­
dargus strigoides (Latham, 1801) & Aegotheles cristatus(Shaw, 1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 1 in Prum et al. (2015)
should be considered the primary reference phylogeny.
Figure 6 in Chen et al. (2019) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Strisores includes over 590 extant species(Billerman et al., 2020; Gill et al., 2020) in the crownclades Caprimulgidae, Steatornis, Nyctibiidae, Podargi­dae, Aegotheles, and Apodiformes, as well as the lastcommon ancestor of those groups and its extinct descendants. A wide variety of extinct taxa have been assigned toStrisores (Mayr, 2009, 2017; Chen et al., 2019).
Diagnostic apomorphies. The only identified potential morphological apomorphy shared by all examined
members of the clade is an elongated crus longum of
the ulnar carpal (Mayr, 2010a). However, other inferredapomorphies widespread within the group include a beakshorter than the rest of the skull (except in Fluviovirida­vis, Podargiformes, and [Eurotrochilus + Trochilidae]),a prominent caudolateral process on the palatine (except
in Fluvioviridavis, Steatornis, and Trochilidae), a shortorbital process of the quadrate (except in Fluvioviridavis
and Steatornis), a pointed mandibular symphysis (except
in Masillapodargus and Batrachostomus), 18 or fewer
presacral vertebrae (except in Steatornithiformes), and along, deep transverse sulcus on the humerus (except in
Podargidae and Trochilidae) (Chen et al., 2019).
Comments. The name Strisores is commonly attributed
to Baird (1858) (including by Chen et al., 2019), but it573

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent clades

was in fact first coined by Cabanis (1847). Some taxonomists have instead used Caprimulgiformes (Cracraft,
2013; Braun et al., 2019; Jarvis et al., 2014; Billerman
et al., 2020; Kuhl et al., 2020) as a name for this clade,occasionally in conjunction with Caprimulgimorphae(Cracraft, 2013; Jarvis et al., 2014). However, we favour the application of Strisores here, as it has nominal
priority over competing names, has seen widespread
recent use in both neontological (Mayr, 2010a; Yuri
et al., 2013; Prum et al., 2015; Kimball et al., 2019;White & Braun, 2019) and palaeontological (Nesbitt
et al., 2011; Mayr, 2017; Chen et al., 2019) literature,
and was originally used for a grouping that included mostmembers of this clade other than Podargidae (Cabanis,1847). In contrast, traditional usage of Caprimulgiformes
excluded all members of Apodiformes. See also comments on Caprimulgiformes.

Podargocypseli Mayr, 2010a [Chen & Field],converted clade nameRegistration number. 385
Definition. The smallest crown clade containing Caprim­
ulgus europaeus Linnaeus, 1758 (Caprimulgidae), Nyct­
ibius (originally Caprimulgus) grandis (Gmelin, 1789)(Nyctibiidae), Podargus (originally Caprimulgus) stri­goides (Latham, 1801) (Podargidae), Aegotheles (originally Caprimulgus) cristatus (Shaw, 1790) (Aegotheli­dae), and Apus (originally Hirundo) apus (Linnaeus,
1758) (Apodiformes) but not Steatornis caripensis Humboldt, 1817 (Steatornithidae). This is a minimum-crownclade definition.
Abbreviated definition. Min crown ∇ (Caprimulgus eu­
ropaeus Linnaeus, 1758 & Nyctibius grandis (Gmelin,1789) & Podargus strigoides (Latham, 1801) & Aego­
theles cristatus (Shaw, 1790) & Apus apus (Linnaeus,
1758) ~ Steatornis caripensis Humboldt, 1817).
Reference phylogeny. Figure 3 in Mayr (2010a) should
be considered the primary reference phylogeny.
Composition. Podargocypseli is hypothesized to include
the crown clades Caprimulgidae, Nyctibiidae, Podargi­dae, Aegotheles, and Apodiformes, as well as the last com­
mon ancestor of those groups and its extinct descendants.
Diagnostic apomorphies. Mayr (2010a) recovered a pro­minent caudolateral process on the palatine and 18 or
few­er presacral vertebrae as apomorphies of this group.
Under the total-evidence topologies found by Chen et al.
(2019), Podargocypseli does not exist, and these features
are instead optimized as apomorphies of Strisores. Mayr
(2010a) additionally noted that the ability to enter torpor is
widespread in Podargocypseli; it is likely that this character would also be inferred to be an apomorphy of Strisores
in the total-evidence topologies of Chen et al. (2019).
574

Comments. Mayr (2010a) coined this name in accordance with a specific phylogenetic hypothesis, which isreflected by our proposed definition. This name is inapplicable to topologies in which this grouping is notmonophyletic (e.g., Fig. 1; Hackett et al., 2008; Ksepka et al., 2013; Prum et al., 2015; Reddy et al., 2017;
Chen et al., 2019; White & Braun, 2019; Kuhl et al.,2020).

Cypselomorphae Huxley, 1867 [Chen & Field],converted clade nameRegistration number. 386
Definition. The total clade containing Caprimulgus eu­
ropaeus Linnaeus, 1758 (Caprimulgidae), Nyctibius(originally Caprimulgus) grandis (Gmelin, 1789) (Nycti­biidae), Aegotheles (originally Caprimulgus) crista­tus (Shaw, 1790) (Aegothelidae), and Apus (originally
Hirundo) apus (Linnaeus, 1758) (Apodiformes) but not
Steatornis caripensis Humboldt, 1817 (Steatornithi­dae) and Podargus (originally Caprimulgus) strigoides(Latham, 1801) (Podargidae). This is a total-clade definition.
Abbreviated definition. Total ∇ (Caprimulgus euro­
paeus Linnaeus, 1758 & Nyctibius grandis (Gmelin,1789) & Aegotheles cristatus (Shaw, 1790) & Apus apus
(Linnaeus, 1758) ~ Steatornis caripensis Humboldt,
1817 & Podargus strigoides (Latham, 1801)).
Reference phylogeny. Figure 3 in Mayr (2010a) should
be considered the primary reference phylogeny. Figure 2
in Ksepka et al. (2013) may be regarded as a secondaryreference phylogeny.
Composition. Cypselomorphae is hypothesized to include the crown clades Caprimulgidae, Nyctibiidae,
Aegotheles, and Apodiformes, as well as all extinct taxa
more closely related to these taxa than to any other extant
taxon.
Diagnostic apomorphies. Mayr (2010a) recovered ashort, wide beak with narial openings extending into its
tip, a reduced orbital process of the quadrate, a deep, narrow furrow separating the lateral and medial condyles of
the quadrate, narrow distal mandibular rami meeting in avery short symphysis, a furcula with distinct articulation
surfaces for the acrocoracoid processes of the coracoid,and a cerebellum with a reduced anterior lobe and a relatively large posterior lobe as apomorphies of this group.
Under the total-evidence topologies found by Chen et al.
(2019), Cypselomorphae does not exist, and these features are instead optimized as symplesiomorphies or asapomorphies of Strisores.
Comments. Mayr (2004) recruited this name in accordance with a specific phylogenetic hypothesis matching theVERTEBRATE ZOOLOGY — 70 (4) 2020

original scope of the name ascribed by Huxley (1867),
which is reflected by our proposed definition. This nameis inapplicable to topologies in which this grouping is notmonophyletic (e.g., Fig. 1; Hackett et al., 2008; Prumet al., 2015; Reddy et al., 2017; Chen et al., 2019; White& Braun, 2019; Kuhl et al., 2020).

Caprimulgi Ridgway, 1881 [Chen & Field],converted clade nameRegistration number. 387
Definition. The smallest crown clade containing Capri­
mulgus europaeus Linnaeus, 1758 (Caprimulgidae) andNyctibius (originally Caprimulgus) grandis (Gmelin,1789) (Nyctibiidae) but not Steatornis caripensis Humboldt, 1817 (Steatornithidae), Podargus (originally Ca­pri­mul­gus) strigoides (Latham, 1801) (Podargidae), Ae­
gotheles (originally Caprimulgus) cristatus (Shaw, 1790)(Aegothelidae), and Apus (originally Hirundo) apus (Lin­naeus, 1758) (Apodiformes). This is a minimum-crownclade definition.
Abbreviated definition. Min crown ∇ (Caprimulgus eu­
ropaeus Linnaeus, 1758 & Nyctibius grandis (Gmelin,1789) ~ Steatornis caripensis Humboldt, 1817 & Podar­
gus strigoides (Latham, 1801) & Aegotheles cristatus(Shaw, 1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 3 in Mayr (2010a) should
be considered the primary reference phylogeny. Figure 2
in Ksepka et al. (2013) may be regarded as a secondaryreference phylogeny.
Composition. Caprimulgi is hypothesized to include thecrown clades Caprimulgidae and Nyctibiidae, as well as
the last common ancestor of those groups and its extinct
descendants.
Diagnostic apomorphies. Mayr (2010a) recovered a laterally widened palatine, strongly protruding paroccipital
processes, a cone-like protrusion at the caudal margin of
the optic nerve foramen, caudally flattened mandibularrami with an intramandibular joint, 17 cervical vertebrae, and an intertarsal sesamoid as apomorphies of thisgroup. Additionally, caprimulgids and nyctibiids are theonly members of Strisores in which the presence of a tapetum lucidum has been confirmed (Braun & Huddleston, 2009). Under the total-evidence topologies found byChen et al. (2019), Caprimulgi does not exist, and manyof these features are optimized as having been independently acquired by caprimulgids and nyctibiids, though
it is possible that at least some of them were ancestrally
present in Strisores.
Comments. Mayr (2010a) recruited this name in accordance with a specific phylogenetic hypothesis, whichis reflected by our proposed definition. This name is in-applicable to topologies in which this grouping is notmonophyletic (e.g., Fig. 1; Hackett et al., 2008; Prumet al., 2015; Reddy et al., 2017; Chen et al., 2019; White& Braun, 2019; Kuhl et al., 2020).

Caprimulgiformes Shufeldt, 1904 [Chen &Field], converted clade nameRegistration number. 388
Definition. The total clade containing Caprimulgus euro­
paeus Linnaeus, 1758 (Caprimulgidae) but not Steator­
nis caripensis Humboldt, 1817 (Steatornithidae), Nycti­bius (originally Caprimulgus) grandis (Gmelin, 1789)(Nyctibi­idae), Podargus (originally Caprimulgus) stri­go­i­des (Latham, 1801) (Podargidae), Aegotheles (ori­gi­
nally Caprimulgus) cristatus (Shaw, 1790) (Aegotheli­dae), and Apus (originally Hirundo) apus (Linnaeus,
1758) (Apodiformes). This is a total-clade definition.
Abbreviated definition. Total ∇ (Caprimulgus euro­
paeus Linnaeus, 1758 ~ Steatornis caripensis Humboldt,
1817 & Nyctibius grandis (Gmelin, 1789) & Podargus
strigoides (Latham, 1801) & Aegotheles cristatus (Shaw,
1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Caprimulgiformes includes the crownclade Caprimulgidae and all extinct taxa more closely
related to it than to any other extant taxon. No stem
caprimulgids have yet been identified through phylogenetic analysis, though close affinities to Caprimulgidae
have been hypothesized for some fragmentary Eocene
specimens (Mourer-Chauviré, 1988; Mayr, 2009).
Comments. Caprimulgiformes is typically attributed to
Ridgway (1881), likely because he was the first to use
the genus Caprimulgus as the basis for an ordinal-level
name, which he spelled Caprimulgi. However, under
the PhyloCode, names that have been subjected to suchstandardization should be attributed to the author who
introduced the new spelling, at least in cases for which
the original authorship can be ascertained (Notes 9.15A.4
and 19.5.1). The oldest use of the spelling Caprimulgi­
formes that we have been able to locate was by Shufeldt(1904), thus we tentatively attribute nominal authorshipto him here.
Traditionally, the name Caprimulgiformes was used
to unite the nocturnal and crepuscular members of Stri­
sores (Caprimulgidae, Steatornithidae, Nyctibiidae, Po­dargidae, and Aegothelidae), which in recent phylogenetic analyses have been uniformly found to constitutea paraphyletic grade with respect to Apodiformes. As
575

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent clades

noted previously, many modern taxonomic authorities
now use Caprimulgiformes to refer to a monophyletic
group equivalent to Strisores. Although this would bejustifiable under PhyloCode Article 10.1, we favour theuse of the latter name for that clade (see comments on
Strisores).
When used for a monophyletic group, the other mostcommon application of Caprimulgiformes is to limit it
to Caprimulgidae among extant members of Strisores(e.g., Yuri et al., 2013; Piacentini et al., 2015; Mayr,
2017; Chen et al., 2019; Chesser et al., 2019). Under
phylogenetic nomenclature, it has been customary to assign crown-clade definitions to avian clade names withthe suffix “-iformes” (ranked at the level of order in Linnaean taxonomy), consistent with PhyloCode Recommendation 10.1B (Sangster, 2020b, c, d, e, f). However,clades with the suffix “-iformes” that only contain one
extant taxon with the suffix “-idae” (ranked at the levelof family in Linnaean taxonomy) present an unusual situation in which both the ordinal and familial names tend
to be commonly used, but would refer to the same crownclade if both are given crown-clade definitions, rendering the two names synonymous under the PhyloCode. In
cases like these, recent authors who employ phylogenetic
nomenclature have often followed the spirit of Recommendation 10G (which only mentions genus names) andrecommended limiting names with the suffix “-idae” tothe crown group, while retaining use of the corresponding “-iformes” names for more inclusive clades encompassing all or part of the appropriate stem group (e.g.,
Clarke et al., 2003; Ksepka & Clarke, 2009; Nesbitt
et al., 2011). We have opted to follow this recommendation here for relevant clade names such as Caprimulgi­
formes and Caprimulgidae, an approach that will bothpreserve widely used names and continue a practice established in recent literature.

Caprimulgidae Vigors, 1825 [Chen & Field],converted clade nameRegistration number. 389
Definition. The smallest crown clade containing Euro­
sto­podus (originally Caprimulgus) mystacalis (Temminck, 1826), Lyncornis (originally Caprimulgus) ma­
cro­tis (Vi­gors in Kirby, 1831), and Caprimulgus euro­pae­us Linnaeus, 1758. This is a minimum-crown-clade
definition.
Abbreviated definition. Min crown ∇ (Eurostopodus
mystacalis (Temminck, 1826) & Lyncornis macrotis (Vigors, 1831) & Caprimulgus europaeus Linnaeus, 1758).
Reference phylogeny. Figure 3 in Sigurðsson & Cra­

craft (2014) should be considered the primary reference

phylogeny. Figure 2 in Han et al. (2010) and Figure 4 in
White et al. (2016) may be regarded as secondary reference phylogenies.
576

Composition. Caprimulgidae includes 98 extant species(Billerman et al., 2020; Gill et al., 2020). Potential fossil representatives have been identified, but are largely
limited to Quaternary deposits (Manegold, 2010).
Diagnostic apomorphies. Most morphological character states that have been optimized as apomorphies for
Caprimulgidae have also been found in Nyctibiiformes(see comments on Caprimulgi). However, caprimulgids
can be distinguished from nyctibiiforms by having a long,
slender rostromedial process on the palatine as well as thelonger olecranon process on their ulna (Chen et al., 2019).
Comments. See comments on Caprimulgiformes.

Vanescaves Chen, White, Benson, Braun, &Field, 2019 [Chen & Field], converted clade
nameRegistration number. 390
Definition. The smallest crown clade containing Stea­
tornis caripensis Humboldt, 1817 (Steatornithiformes),
Nyc­tibius (originally Caprimulgus) grandis (Gmelin,1789) (Nyctibiiformes), Podargus (originally Caprimul­gus) strigoides (Latham, 1801) (Podargiformes), Aego­
theles (originally Caprimulgus) cristatus (Shaw, 1790)(Aegotheliformes), and Apus (originally Hirundo) apus
(Lin­naeus, 1758) (Apodiformes) but not Caprimulgus
euro­paeus Linnaeus, 1758 (Caprimulgiformes). This is aminimum-crown-clade definition.
Abbreviated definition. Min crown ∇ (Steatornis cari­
pensis Humboldt, 1817 & Nyctibius grandis (Gmelin,1789) & Podargus strigoides (Latham, 1801) & Aego­
the­les cristatus (Shaw, 1790) & Apus apus (Linnaeus,
1758) ~ Caprimulgus europaeus Linnaeus, 1758).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Vanescaves is hypothesized to include thecrown clades Steatornis, Nyctibiidae, Podargidae, Ae­
gotheles, and Apodiformes, as well as the last common
ancestor of those groups and its extinct descendants.
Diagnostic apomorphies. This clade has primarily been
recovered using molecular data (Prum et al., 2015; Chenet al., 2019; White & Braun, 2019; Kuhl et al., 2020).
One morphological character state that has been identi­
fied as a potential apomorphy is a poorly developed de­scending process on the lacrimal (Chen et al., 2019).
Comments. Chen et al. (2019) coined this name in accordance with a specific phylogenetic hypothesis, which

VERTEBRATE ZOOLOGY — 70 (4) 2020is reflected by our proposed definition. This name is inapplicable to topologies in which this grouping is notmonophyletic (e.g., Hackett et al., 2008; Mayr, 2010a;
Ksepka et al., 2013; Reddy et al., 2017).

Sedentaves Chen & Field, new clade nameRegistration number. 422
Definition. The smallest crown clade containing Steator­
nis caripensis Humboldt, 1817 (Steatornithiformes) andNyctibius (originally Caprimulgus) grandis (Gmelin,1789) (Nyctibiiformes) but not Caprimulgus europaeusLin­naeus, 1758 (Caprimulgiformes), Podargus (originally Caprimulgus) strigoides (Latham, 1801) (Podargi­
for­mes), Aegotheles (originally Caprimulgus) cristatus(Shaw, 1790) (Aegotheliformes), and Apus (originallyHi­run­do) apus (Linnaeus, 1758) (Apodiformes). This isa mi­ni­mum-crown-clade definition.
Abbreviated definition. Min crown ∇ (Steatornis cari­
pensis Humboldt, 1817 & Nyctibius grandis (Gmelin,1789) ~ Caprimulgus europaeus Linnaeus, 1758 & Po­
dar­gus strigoides (Latham, 1801) & Aegotheles cristatus(Shaw, 1790) & Apus apus (Linnaeus, 1758)).
Etymology. From Latin sedentes (sitting) and aves(birds), referring to the shortened tarsometatarsus ofthese birds and their habit of remaining perched for long
periods of time.
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Sedentaves is hypothesized to include thecrown clades Steatornis and Nyctibiidae, as well as thelast common ancestor of those groups and its extinct descendants.
Diagnostic apomorphies. This clade has primarily been
recovered using molecular data (Hackett et al., 2008;
Prum et al., 2015; Reddy et al., 2017; Chen et al., 2019;White & Braun, 2019; Kuhl et al., 2020), but morphological character states that have been optimized
as potential apomorphies include the absence of a supratendinal bridge on the tibiotarsus and an extremely
short tarsometatarsus (Mayr, 2010a; Chen et al., 2019).
Extant representatives of Sedentaves share present-day
geographic distributions restricted to the Neotropics,
though these may merely reflect the outcome of formerly widespread distributions that have contracted towards
low latitudes throughout the Cenozoic (Olson , 1987;
Mourer-Chauviré, 1989; Mayr, 1999, 2005, 2009; Saupe
et al., 2019).

Comments. We coin this name in accordance with a specific phylogenetic hypothesis, which is reflected by our
proposed definition. This name is inapplicable to topologies in which this grouping is not monophyletic (e.g.,Mayr, 2010a; Ksepka et al., 2013).

Steatornithiformes Mayr, 2010a [Chen &Field], converted clade nameRegistration number. 391
Definition. The total clade containing Steatornis carip­
ensis Humboldt, 1817 (Steatornithidae) but not Caprim­
ulgus europaeus Linnaeus, 1758 (Caprimulgidae), Nyct­
ibius (originally Caprimulgus) grandis (Gmelin, 1789)(Nyctibiidae), Podargus (originally Caprimulgus) stri­goides (Latham, 1801) (Podargidae), Aegotheles (originally Caprimulgus) cristatus (Shaw, 1790) (Aegotheli­dae), and Apus (originally Hirundo) apus (Linnaeus,
1758) (Apodiformes). This is a total-clade definition.
Abbreviated definition. Total ∇ (Steatornis caripensis
Humboldt, 1817 ~ Caprimulgus europaeus Linnaeus,
1758 & Nyctibius grandis (Gmelin, 1789) & Podargus
strigoides (Latham, 1801) & Aegotheles cristatus (Shaw,
1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Steatornithiformes includes the crownclade Steatornis and all extinct taxa more closely related
to it than to any other extant taxon. The Eocene Prefica
has been hypothesized to be on the stem of Steatornis (Ol­son, 1987), which has been consistently supported by phy­lo­genetic analysis (Mayr, 2005; Ksepka et al., 2013; Chenet al., 2019). Other extinct members of this lineage might
include Euronyctibius (Mourer-Chauviré, 2013), Flu­vio­
vi­ri­davis, and Protocypselomorphus (Chen et al., 2019).
Diagnostic apomorphies. Potential apomorphies include
19 or more presacral vertebrae and a tibiotarsus as long asor shorter than the carpometacarpus (Chen et al., 2019).
Comments. See comments on Caprimulgiformes. As
noted by Chen et al. (2019) and originally indicated by
Mayr (2010a), this name is correctly attributed to Mayr
(2010a) instead of Sharpe (1891).

Steatornis Humboldt in Humboldt & Bonpland,
1814 [Chen & Field], converted clade nameRegistration number. 392
577

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent clades

Definition. The smallest clade containing Steatornis ca­ri­pensis Humboldt, 1817. This is a directly-specifiedancestor definition.
Abbreviated definition. Min ∇ (Steatornis caripensis
Humboldt, 1817).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Steatornis includes a single extant species, Steatornis caripensis (Billerman et al., 2020; Gill
et al., 2020).
Comments. Per PhyloCode Recommendation 10G, incases where a crown clade contains a single genus in current classifications, the genus name should preferably beconverted as the name of that crown clade irrespectiveof whether higher-ranked taxa have been named for thesame clade (in this case Steatornithidae, which we do notconvert). This recommendation is followed here. Stea­
tornis is considered a crown clade by PhyloCode Note
9.9.2, as we have assigned it a directly-specified-ancestor definition with an extant internal specifier, though inpractice under some species concepts, this name may infact be applied to a clade slightly more inclusive than thecrown.

Nyctibiiformes Yuri, Kimball, Harshman,
Bowie, Braun, Chojnowski, Han, Hackett,
Huddleston, Moore, Reddy, Sheldon, Steadman, Witt, & Braun, 2013 [Chen & Field],converted clade nameRegistration number. 393
Definition. The total clade containing Nyctibius (originally Caprimulgus) grandis (Gmelin, 1789) (Nyctibi­i­dae)
but not Caprimulgus europaeus Linnaeus, 1758 (Ca­pri­mul­gidae), Steatornis caripensis Humboldt, 1817 (Stea­
tor­nithidae), Podargus (originally Caprimulgus) strigoi­
des (Latham, 1801) (Podargidae), Aegotheles (originally
Caprimulgus) cristatus (Shaw, 1790) (Aegothelidae), andApus (originally Hirundo) apus (Linnaeus, 1758) (Apo­diformes). This is a total-clade definition.
Abbreviated definition. Total ∇ (Nyctibius grandis(Gmelin, 1789) ~ Caprimulgus europaeus Linnaeus,
1758 & Steatornis caripensis Humboldt, 1817 & Podar­
gus stri­goides (Latham, 1801) & Aegotheles cristatus(Shaw, 1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &578

Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Nyctibiiformes includes the crown clade
Nyctibiidae and all extinct taxa more closely related toit than to any other extant taxon. The Eocene Parapre­
fica is a probable stem nyctibiid (Mayr, 2005; Ksepka
et al., 2013; Chen et al., 2019).
Diagnostic apomorphies. Most morphological character states that have been optimized as apomorphies for
Nyctibiiformes have also been found in Caprimulgidae(see comments on Caprimulgi). However, nyctibiiforms
can be distinguished from caprimulgids by the more pronounced curvature of the jugal arches and mandibles, theabsence of a supratendinal bridge on the tibiotarsus, andan extremely short tarsometatarsus (Mayr, 2005). As noted above, the latter two characters may be apomorphies
shared between Steatornithiformes and Nyctibiiformes.
Comments. See comments on Caprimulgiformes.

Nyctibiidae Sharpe, 1891 [Chen & Field],converted clade nameRegistration number. 394
Definition. The smallest crown clade containing Phyl­laemulor (originally Nyctibius) bracteatus (Gould in Yarrell, 1846), Nyctibius (originally Caprimulgus) grandis(Gmelin, 1789), and Nyctibius (originally Caprimulgus)
griseus (Gmelin, 1789). This is a minimum-crown-clade
definition.
Abbreviated definition. Min crown ∇ (Phyllaemulor
bracteatus (Gould, 1846) & Nyctibius grandis (Gmelin,1789) & Nyctibius griseus (Gmelin, 1789)).
Reference phylogeny. Figure 3 in White et al. (2017)
should be considered the primary reference phylogeny.
Composition. Nyctibiidae includes 7 extant species (Bil­lerman et al., 2020; Gill et al., 2020).

Diagnostic apomorphies. Morphological phylogenetic
studies focusing on Strisores generally have not broadly sampled members of Nyctibiidae. However, Mayr
(2005) noted that extant nyctibiids differ from the stem
nyctibiid Paraprefica in details of the skull, coracoid, andcarpometacarpus. Notably, Paraprefica lacks a tooth-likeprojection on the maxilla, which is found in all nyctibiids(Costa & Donatelli, 2009; Costa et al., 2018).
Comments. See comments on Caprimulgiformes. Under
the International Code of Zoological Nomenclature (ICZN,
1999), this name is attributed to Chenu & des Murs
(1851) (who coined it with the spelling Nyctibiines). As
noted under comments on Caprimulgiformes, how­ever,VERTEBRATE ZOOLOGY — 70 (4) 2020

the PhyloCode treats attribution of names that have been
amended to a standardized suffix under a rank-­based code
differently. The oldest use of the spelling Nyc­ti­bi­idae that
we have been able to locate was by Sharpe (1891), thus
we tentatively attribute nominal author­ship to him here.

Letornithes Chen & Field, new clade nameRegistration number. 423
Definition. The smallest crown clade containing Podar­gus (originally Caprimulgus) strigoides (Latham, 1801)(Po­dar­gi­formes), Aegotheles (originally Caprimulgus)
cris­ta­­tus (Shaw, 1790) (Aegotheliformes), and Apus (ori­gi­nal­ly Hirundo) apus (Linnaeus, 1758) (Apodifor­mes)
but not Caprimulgus europaeus Linnaeus, 1758 (Ca­pri­mul­gi­for­mes), Steatornis caripensis Humboldt, 1817
(Stea­tor­ni­thi­formes), and Nyctibius (originally Capri­mul­gus) grandis (Gmelin, 1789) (Nyctibiiformes). This is aminimum-crown-clade definition.
Abbreviated definition. Min crown ∇ (Podargus strigoi­
des (Latham, 1801) & Aegotheles cristatus (Shaw, 1790)& Apus apus (Linnaeus, 1758) ~ Caprimulgus europaeus
Linnaeus, 1758 & Steatornis caripensis Humboldt, 1817
& Nyctibius grandis (Gmelin, 1789)).
Etymology. From the Greek goddess Leto and ornithes(birds). Leto was the mother of both Artemis (goddessof the moon and the hunt) and Apollo (god of the sun
and the arts), reflected by the membership of this cladein the nocturnal Podargidae, the larger species of which
are known to hunt vertebrate prey (Serventy, 1936;
Billerman et al., 2020), and the diurnal Apodiformes,
in which elaborate visual and acoustic displays have
evolved (Clark & Feo, 2008; Feo & Clark, 2010; Zusi
& Gill, 2009; Clark, 2011; Clark et al., 2018; Simpson & McGraw, 2018; Billerman et al., 2020; Eliason
et al., 2020). In one myth recounted by Ovid’s Metamor­
phoses, Leto turns a group of Lycian peasants into frogs,
which hearkens to the vernacular name “frogmouth” forthe Podargidae. Leto was also the sister of Asteria, thenamesake for the oldest known crown bird, Asteriornis
maastrichtensis (Field et al., 2020).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Letornithes is hypothesized to include thecrown clades Podargidae and Daedalornithes, as well as
the last common ancestor of those groups and its extinct
descendants.
Diagnostic apomorphies. This clade has primarily been
recovered using molecular data (Prum et al., 2015; Red-dy et al., 2017; Chen et al., 2019; White & Braun, 2019;

Kuhl et al., 2020), but a morphological character statethat has been optimized as a potential apomorphy is theabsence of a distal interosseus canal on the tarsometatarsus (Chen et al., 2019). Members of this group also share
the absence of basipterygoid processes (Mayr, 2010a).
Comments. We coin this name in accordance with a
specific phylogenetic hypothesis, which is reflected byour proposed definition. This name is inapplicable totopo­logies in which this grouping is not monophyletic(e.g., Hackett et al., 2008; Mayr, 2010a; Ksepka et al.,2013).

Podargiformes Mathews, 1918 [Chen & Field],converted clade nameRegistration number. 395
Definition. The total clade containing Podargus (originally Caprimulgus) strigoides (Latham, 1801) (Podargi­dae)
but not Caprimulgus europaeus Linnaeus, 1758 (Ca­pri­mul­gi­dae), Steatornis caripensis Humboldt, 1817 (Stea­
tor­ni­thi­dae), Nyctibius (originally Caprimulgus) gran­dis (Gmelin, 1789) (Nyctibiidae), Aegotheles (originally
Caprimulgus) cristatus (Shaw, 1790) (Aegothelidae), andApus (originally Hirundo) apus (Linnaeus, 1758) (Apodi­
formes). This is a total-clade definition.
Abbreviated definition. Total ∇ (Podargus strigoides(La­tham, 1801) ~ Caprimulgus europaeus Linnaeus, 1758
& Steatornis caripensis Humboldt, 1817 & Nycti­bius
grandis (Gmelin, 1789) & Aegotheles cristatus (Shaw,
1790) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Podargiformes includes the crown clade
Podargidae and all extinct taxa more closely related toit than to any other extant taxon. The Eocene Masillapo­
dargus is a probable stem podargid (Mayr, 1999; Nesbitt et al., 2011; Ksepka et al., 2013; Mayr, 2015a; Chenet al., 2019). Other potential stem podargids include Flu­
vioviridavis (Nesbitt et al., 2011; Ksepka et al., 2013)
and Quercypodargus (Mourer-Chauviré, 1989).
Diagnostic apomorphies. A large number of apomorphies differentiating Podargiformes from most othermembers of Strisores have been identified. These include
a fossa on the ventral surface of palatine anterior to thechoana, a rounded posterior edge of the articular portionof the mandible, a straight ventral margin of the mandibular ramus, a continuous lateral concavity on the mandible, a shallow transverse sulcus on the humerus, and a579

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent clades

distal wing skeleton shorter than the humerus (Nesbitt
et al., 2011; Chen et al., 2019). Some of these features
are also found in Fluvioviridavis (Nesbitt et al., 2011),
whose assignment to this clade is debated (Mayr, 2015a;
Chen et al., 2019).

Aegotheliformes Worthy, Tennyson, Jones,
McNamara, & Douglas, 2007 [Chen & Field],converted clade nameComments. See comments on Caprimulgiformes.

Definition. The total clade containing Aegotheles (originally Caprimulgus) cristatus (Shaw, 1790) (Aegotheli­dae) but not Caprimulgus europaeus Linnaeus, 1758
(Caprimulgidae), Steatornis caripensis Humboldt, 1817
(Steatornithidae), Nyctibius (originally Caprimulgus)
grandis (Gmelin, 1789) (Nyctibiidae), Podargus (originally Caprimulgus) strigoides (Latham, 1801) (Podar­
gidae), and Apus (originally Hirundo) apus (Linnaeus,
1758) (Apodiformes). This is a total-clade definition.

Podargidae Sclater, 1880 [Chen & Field],converted clade nameRegistration number. 396
Definition. The smallest crown clade containing Rigi­di­­penna inexpectata (originally Podargus inexpectatus
Hartert in Sclater, 1901), Podargus (originally Caprimul­gus) strigoides (Latham, 1801), and Batrachostomus (ori­ginally Podargus) auritus (Gray in Griffith, 1829). This isa minimum-crown-clade definition.
Abbreviated definition. Min crown ∇ (Rigidipenna in­
expectata (Hartert, 1901) & Podargus strigoides (Latham,1801) & Batrachostomus auritus (Gray, 1829)).
Reference phylogeny. Figure 1c in Oliver et al. (2020)should be considered the primary reference phylogeny.
Composition. Podargidae includes 16 extant species (Bil­­lerman et al., 2020; Gill et al., 2020).

Diagnostic apomorphies. Potential apomorphies include “horns” on the skull projecting posteriorly in frontof the orbits and palatines fused anterior to the choanae(Nesbitt et al., 2011; Chen et al., 2019). Rigidipenna has
not been sampled in morphological phylogenetic studies focusing on Strisores, but available osteological descriptions do not mention the absence of these characters(Cleere et al., 2007).
Comments. See comments on Caprimulgiformes. Under
the ICZN’s Principle of Coordination (Article 36), thisname is attributed to Bonaparte (1838) (who coined Po­
darginae at the rank of subfamily). However, the Phylo­
Code ignores the ICZN ’s Principle of Coordination in determining nominal authorship (Note 9.15A.3). The oldest
use of Podargidae that we have been able to locate wasby Sclater (1880), thus we tentatively attribute nominal
authorship to him here.
Batrachostomus auritus (the type species of Batra­chostomus) was not sampled in the reference phylogeny,
but three congeners were included.

Registration number. 397

Abbreviated definition. Total ∇ (Aegotheles cristatus(Shaw, 1790) ~ Caprimulgus europaeus Linnaeus, 1758
& Steatornis caripensis Humboldt, 1817 & Nyctibius
grandis (Gmelin, 1789) & Podargus strigoides (Latham,1801) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Aegotheliformes includes the crown clade
Aegotheles and all extinct taxa more closely related to it
than to any other extant taxon. The Miocene Quipollornis
has been hypothesized to be a stem aegothelid based oncomparative anatomy (Rich & McEvey, 1977). Chenet al. (2019) suggested that the Eocene Hassiavis may
also represent a stem aegothelid, though strong support
for this hypothesis was only found in one of their phylogenetic analyses.
Comments. See comments on Caprimulgiformes. As
noted by Mayr (2010a), this name is correctly attributed
to Worthy et al. (2007) instead of Simonetta (1967).

Aegotheles Vigors & Horsfield, 1827 [Chen &Field], converted clade nameRegistration number. 398
Definition. The smallest crown clade containing Aego­
theles savesi Layard & Layard, 1881, Aegotheles insignis
Salvadori, 1875, and Aegotheles (originally Caprimul­gus) cristatus (Shaw, 1790). This is a minimum-crownclade definition.
Abbreviated definition. Min crown ∇ (Aegotheles save­si Layard & Layard, 1881 & Aegotheles insignis Salvadori, 1875 & Aegotheles cristatus (Shaw, 1790)).

580

VERTEBRATE ZOOLOGY — 70 (4) 2020

Reference phylogeny. Figure 1b in Dumbacher et al.
(2003) should be considered the primary reference phylogeny.
Composition. Aegotheles includes up to 10 extant species (Billerman et al., 2020; Gill et al., 2020). A Miocene fossil has been assigned to this genus, though its
relationships to extant members of this clade remain unclear (Worthy et al., 2007).
Comments. See comments on Steatornis.

Pan-Apodiformes Ksepka, Clarke, Nesbitt,
Kulp, & Grande, 2013 [Chen & Field],converted clade nameRegistration number. 399
Definition. The total clade containing Apus (originally
Hirundo) apus (Linnaeus, 1758) (Apodiformes) but not
Caprimulgus europaeus Linnaeus, 1758 (Ca­pri­mul­­gi­­dae), Steatornis caripensis Humboldt, 1817 (Stea­tor­ni­­thi­dae), Nyctibius (originally Caprimulgus) grandis(Gmelin, 1789) (Nyctibiidae), Podargus (originally Ca­pri­mulgus) strigoides (Latham, 1801) (Podargidae), andAegotheles (originally Caprimulgus) cristatus (Shaw,
1790) (Aegothelidae). This is a total-clade definition.
Abbreviated definition. Total ∇ (Apus apus (Linnaeus,
1758) ~ Caprimulgus europaeus Linnaeus, 1758 & Stea­
tornis caripensis Humboldt, 1817 & Nyctibius grandis(Gmelin, 1789) & Podargus strigoides (Latham, 1801)& Aegotheles cristatus (Shaw, 1790)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.

Apodi Peters, 1940 [Chen & Field],converted clade nameRegistration number. 400
Definition. The smallest crown clade containing Hemi­
procne (originally Hirundo) longipennis (Rafinesque,1802) (Hemiprocnidae) and Apus (originally Hirundo)
apus (Linnaeus, 1758) (Apodidae). This is a minimumcrown-clade definition.
Abbreviated definition. Min crown ∇ (Hemiprocne lon­gi­pennis (Rafinesque, 1802) & Apus apus (Linnaeus,
1758)).
Reference phylogeny. Figure 6 in Chen et al. (2019)should be considered the primary reference phylogeny.
Figure 1 in Prum et al. (2015) and Figure 6 in White &Braun (2019) may be regarded as secondary reference
phylogenies.
Composition. Apodi includes the crown clades Hemi­
procne and Apodidae, as well as the last common ancestor of those groups and its extinct descendants.
Diagnostic apomorphies. Potential apomorphies include
an elongated, narrow ventral supracondylar tubercle on
the humerus, a marked tubercle on the ventral side of theradial shaft opposing the carpal tubercle of the ulna, andgreatly elongated outer primary feathers (Mayr, 2010b).
Comments. This name has consistently been used in reference to the group uniting Hemiprocne and Apodidae(Peters, 1940; Harrison, 1984; Mayr, 2010a), which isreflected by our proposed definition. Hemiprocne longi­
pennis (the type species of Hemiprocne) was not sampled
in the reference phylogenies, but Chen et al. (2019) andWhite & Braun (2019) included the congener H. mysta­
cea and Prum et al. (2015) included the congener H. co­mata.

Composition. Pan-Apodiformes includes the crown clade
Apodiformes and all extinct taxa more closely related to it
than to any other extant taxon. The Eocene Eocypselus isa probable stem apodiform (Mayr, 2010b; Ksepka et al.,2013; Chen et al., 2019). Other potential stem apodi­forms
include the Aegialornithidae (Mayr, 2009, 2010b).

Hemiprocne Nitzsch, 1829 [Chen & Field],converted clade name

Diagnostic apomorphies. Potential apomorphies include an abbreviated humerus and an ossified supratendinal bridge (arcus extensorius) on the tarsometatarsus(Mayr, 2010b; Ksepka et al., 2013; Chen et al., 2019).

Definition. The largest crown clade containing Hemi­
procne (originally Hirundo) longipennis (Rafinesque,1802) (Hemiprocnidae) but not Apus (originally Hirun­do) apus (Linnaeus, 1758) (Apodidae). This is a maximum-crown-clade definition.

Comments. Ksepka et al. (2013) attributed this name toMayr (2010b). However, we have not been able to locate
any use of the name Pan-Apodiformes in Mayr (2010b),
who instead used Apodiformes for a more inclusive clade
including the stem apodiform Eocypselus. To our knowledge, Ksepka et al. (2013) were the first to use Pan-Apo­
diformes in scientific literature.

Registration number. 401

Abbreviated definition. Max crown ∇ (Hemiprocne
longipennis (Rafinesque, 1802) ~ Apus apus (Linnaeus,
1758)).
Reference phylogeny. Figure 6 in White & Braun(2019) should be considered the primary reference phy581

Chen, A. & Field, D. J.: Phylogenetic definitions for Caprimulgimorphae (Aves) and major constituent clades

logeny. Figure 1 in Prum et al. (2015) and Figure 6 inChen et al. (2019) may be regarded as secondary reference phylogenies.
Composition. Hemiprocne includes 4 extant species(Billerman et al., 2020; Gill et al., 2020).
Comments. See comments on Steatornis. Given that toour knowledge no phylogenetic analysis to date has included all four extant species of Hemiprocne, we have
opted for a maximum-crown-clade definition, ensuringthat hypothetical future splits of currently recognized
Hemiprocne species would remain within the clade
Hemiprocne.

Apodidae Olphe-Galliard, 1887 [Chen & Field],converted clade nameRegistration number. 402
Definition. The smallest crown clade containing Cypse­
loides fumigatus (originally Hemiprocne fumigata Streubel, 1848), Streptoprocne (originally Hirundo) zonaris(Shaw, 1796), Collocalia (originally Hirundo) esculenta(Linnaeus, 1758), Chaetura (originally Hirundo) pe­
lagica (Linnaeus, 1758), and Apus (originally Hirundo)
apus (Linnaeus, 1758). This is a minimum-crown-clade
definition.
Abbreviated definition. Min crown ∇ (Cypseloides
fumigatus (Streubel, 1848) & Streptoprocne zonaris(Shaw, 1796) & Collocalia esculenta (Linnaeus, 1758) &Chaetura pelagica (Linnaeus, 1758) & Apus apus (Linnaeus, 1758)).
Reference phylogeny. Figure 1 in Price et al. (2005)
should be considered the primary reference phylogeny.
Composition. Apodidae includes over 110 extant species(Billerman et al., 2020; Gill et al., 2020). Various fossil
specimens dating to the Miocene onwards have been assigned to extant genera (Worthy et al., 2007), with somelocalities preserving an abundance of remains attributable to Apodidae (e.g., Field, 2020), but these have notbeen subjected to phylogenetic analysis.
Diagnostic apomorphies. Many characters that distinguish Apodidae from stem apodids or Hemiprocne haveundergone considerable parallel evolution within Apo­
diformes (Mayr, 2010b, 2015b; Chen et al., 2019), but apotential apomorphy of Apodidae is the great shorteningof the second and third phalanges of pedal digit IV (Chenet al., 2019).
Comments. Cypseloides fumigatus (the type species ofCypseloides) was not sampled in the reference phylogeny, but the congener C. niger was included. Anotherputative congener included in the reference phylogeny,
582“C.” phelpsi, is now classified in the genus Streptoprocne(Billerman et al., 2020; Gill et al., 2020).
Chen et al. (2019) suggested the use of Trochiloidea
for the total group of Trochilidae. However, unknown
to those authors at the time, McGuire et al. (2009) had
already proposed a total-clade definition for Pan-Trochi­
lidae (rendered “Pantrochilidae” in their paper) referringto the same clade (though contra McGuire et al., 2009,
Pan-Trochilidae had been previously coined by Mayr
& Manegold, 2002). McGuire et al. (2009) further
proposed phylogenetic definitions for major constituent clades within Trochilidae. Neither of the authors of
the present contribution were involved with the researchby McGuire et al. (2009), so we refrain from claiming
authorship for their proposed definitions, but we recommend the adoption of their taxonomic scheme in futurestudies that employ phylogenetic nomenclature for totalgroup trochilids.

Acknowledgements
We would like to thank Nico Cellinese und Chris Dell for technicalassistance with registering taxon names in RegNum and Ben Creis­ler for etymological suggestions. Detailed feedback from George
Sangster and an anonymous reviewer greatly improved this manuscript. D.J.F. is supported by UK Research and Innovation Future
Leaders Fellowship MR/S032177/1 and the Isaac Newton Trust.

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