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ARTICLE
A NEW EARLY CRETACEOUS ENANTIORNITHINE (AVES, ORNITHOTHORACES) FROM
NORTHWESTERN CHINA WITH ELABORATE TAIL ORNAMENTATION
JINGMAI K. O’CONNOR,*
,1
DA-QING LI,
2
MATTHEW C. LAMANNA,
3
MIN WANG,
1
JERALD D. HARRIS,
4
JESSIE ATTERHOLT,
5
and HAI-LU YOU
1
1
Key Laboratory of Vertebrate Evolution and Human Origins of the Chinese Academy of Sciences, Institute of Vertebrate
Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xizhimenwai Dajie, Beijing 100044, People’s Republic of
China, jingmai@ivpp.ac.cn; wangmin@ivpp.ac.cn; youhailu@ivpp.ac.cn;
2
Gansu Geological Museum, 6 Tuanjie Road, Chengguan District, Lanzhou, Gansu Province 730010, People’s Republic of China,
daqingligs@gmail.com;
3
Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213,
U.S.A., LamannaM@carnegiemnh.org;
4
Department of Physical Sciences, Dixie State College, 225 South 700 East, Saint George, Utah 84770, U.S.A., jharris@dixie.edu;
5
Department of Integrative Biology, University of California at Berkeley, 1101 Valley Life Sciences Building, Berkeley, California
94720, U.S.A., ajes@berkeley.edu
ABSTRACT—We provide a detailed description of a well-preserved enantiornithine specimen (GSGM-05-CM-004) from
the Lower Cretaceous (Aptian) Xiagou Formation of northwestern Gansu Province, China, for which we erect the new taxon
Feitianius paradisi, gen. et sp. nov. This specimen has a distinctive pelvic morphology and can be further distinguished from
all other Mesozoic birds by a unique caudal plumage formed by multiple rectricial morphotypes. This newly documented tail
morphology reveals a previously unrecognized level of complexity in the plumage of basal birds. This complex tail-feather
morphology has a parallel in extant sexually dimorphic birds in which the males have the most altered tails; thus, we identify
this specimen as male. Ornamental tail morphologies, such as the novel tail plumage described here, dominate
Enantiornithes. This reinforces hypotheses that sexual selection was a major driving force in the evolution of basal bird
plumage.
http://zoobank.org/urn:lsid:zoobank.org:pub:8BEF4422-58C5-487B-B76A-51C5855CF87B
SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP
Citation for this article: O’Connor, J. K., D.-Q. Li, M. C. Lamanna, M. Wang, J. D. Harris, J. Atterholt, and H.-L. You. 2015.
A new Early Cretaceous enantiornithine (Aves, Ornithothoraces) from northwestern China with elaborate tail
ornamentation. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1054035.
INTRODUCTION
Initiated in 2002, renewed paleontological explorations of
exposures of the Lower Cretaceous (Aptian) Xiagou Formation
in the Changma Basin of northwestern Gansu Province, China,
have yielded approximately 100 partial to nearly complete fossil
avian skeletons, many preserved with soft tissues. Although the
majority of these specimens are referable to the ornithuromorph
Gansus yumenensis Hou and Liu, 1984 (You et al., 2006), three
other ornithuromorph species have recently been recognized
based on isolated specimens (Wang et al., 2013), and at least 12
other specimens pertain to Enantiornithes (You et al., 2005;
Harris et al., 2006; Lamanna et al., 2006, 2009; Ji et al., 2011;
Wang et al., 2015), a group that is widely recognized as the domi-
nant clade of Cretaceous landbirds (O’Connor et al., 2011).
None of the Changma enantiornithine specimens preserve either
cranial material or an association of pectoral and pelvic
elements, frustrating attempts to decipher their taxonomy; nev-
ertheless, the collection appears to be taxonomically diverse,
although only two taxa (Ji et al., 2011; Wang et al., 2015) have
been erected to date.
Although most of the Changma enantiornithine specimens are
fragmentary, a few are more complete and anatomically infor-
mative. The most remarkable of these are two articulated partial
specimens, GSGM-05-CM-004 and GSGM-07-CM-001, which
each include the caudal half of the axial skeleton, the pelvic gir-
dle, the hind limbs, and extraordinarily preserved soft tissue
structures (Lamanna et al., 2009). Both specimens preserve
numerous feathers of multiple morphologies; however, the tail
feathers have only been described in GSGM-07-CM-001
(O’Connor et al., 2012). This specimen preserves a pair of elon-
gate, rachis-dominated ‘racket plumes,’ the most common rectri-
cial morphology observed among Early Cretaceous birds,
present in confuciusornithiforms and numerous enantiornithines
(e.g., Bohaiornis guoi Hu et al., 2011, Dapingfangornis sentiso-
rhinus Li et al., 2006, Paraprotopteryx gracilis Zheng et al., 2007,
Protopteryx fengningensis Zhang and Zhou, 2000). Here we
describe the second specimen, GSGM-05-CM-004, which pre-
serves a rectricial morphology that has not been observed in any
*Corresponding author.
Color versions of one or more of the figures in this article can be found
online at www.tandfonline.com/ujvp.
Journal of Vertebrate Paleontology e1054035 (13 pages)
Óby the Society of Vertebrate Paleontology
DOI: 10.1080/02724634.2015.1054035
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other Mesozoic bird but that is reminiscent of the elaborate tails
of some extant sexually dimorphic birds. We erect a new taxon
based on this specimen and discuss the implications of its unique
caudal plumage for our understanding of tail evolution among
basal birds.
Institutional Abbreviations—DNHM, Dalian Natural History
Museum, Dalian, Liaoning Province, China; GSGM, Gansu
Geological Museum, Lanzhou, Gansu Province, China; IVPP,
Institute of Vertebrate Paleontology and Paleoanthropology,
Beijing, China; LPM, Liaoning Paleontological Museum,
Shenyang, Liaoning Province, China.
SYSTEMATIC PALEONTOLOGY
AVES Linnaeus, 1758
ORNITHOTHORACES Chiappe, 1995a
ENANTIORNITHES Walker, 1981
FEITIANIUS PARADISI, gen. et sp. nov.
Holotype—GSGM-05-CM-004, an incomplete but articulated
specimen preserving the caudal half of the skeleton (mostly in
left lateral view) on a single slab, including carbonized vestiges
of the caudal body coverts, rectrices, and keratinous pedal
ungual sheaths.
Diagnosis—A small enantiornithine bird with the unique com-
bination of the following features: shallow pneumatic excava-
tions on the lateral surfaces of the thoracic vertebrae; ilium with
a very small cuppedicus fossa; robust, curved, weakly retroverted
pubis with a dorsally tapered pubic boot; ischium weakly sigmoid
with a delicate ridge inferred for muscle attachment on the cra-
nial half of the lateral surface; medial plantar crest well devel-
oped on the tarsometatarsus, but lateral plantar crest minimally
developed; penultimate pedal phalanges the longest in each digit;
non-ungual phalanges of digit II are dorsoplantarly compressed
and mediolaterally wide; and pedal unguals large and relatively
weakly recurved with long horny sheaths. The species can further
be distinguished by its unique tail plumage, which is composed of
several different rectricial morphotypes (all other known enan-
tiornithines preserve only a single rectricial morphotype).
Etymology—Feitianius paradisi, meaning Paradise’s feitian
(飞天), referring to the hundreds of paintings of feitian, or ‘flying
apsara,’ in the Mogao caves that are not far from the type local-
ity. Like the new species, the feitian were beautiful flying crea-
tures. ‘Paradisi’ (Latin, genitive ‘from paradise’) refers to the
similarity in tail morphology between the new fossil and the
highly sexually dimorphic plumages of extant birds of paradise.
For fun, we decided to masculinize the genus name because the
holotype specimen appears to be a male.
Measurements —See Table 1.
Locality and Horizon—Lower Cretaceous (lower–middle
Aptian) (124–120 Ma; (Suarez et al., 2013) Xiagou Formation,
near Changma Village, Yumen City, Gansu Province, northwest-
ern China.
Taxonomic Remarks—The specimen can be referred to
Enantiornithes based on its possession of the following charac-
ters: excavated thoracic vertebrae with centrally located para-
pophyses; distinctive, large pygostyle with craniodorsal fork,
ventrolateral processes, and distal constriction; ischium with
strap-like proximodorsal process; and reduced metatarsal IV.
Specimen GSGM-05-CM-004 can be differentiated from Qilia-
nia graffini Ji et al., 2011, another enantiornithine from the same
formation, by several features. First, Feitianius paradisi bears a
medial plantar crest on metatarsal II (absent in Q. graffini).
Although the proportions of the pubis and ischium are similar
between the two taxa, the dorsal (caudal) margin of the pubis
and ventral (cranial) margin of the ischium are concave in F.
paradisi, whereas both of these surfaces are relatively straight in
Q. graffini. Furthermore, the proportions of the pedal digits are
quite different: the combined length of digit III compared with
that of metatarsal III is 1.05 in the new species compared with
0.92 in Q. graffini; the same ratio for digit II is 0.77 in F. paradisi
and 0.70 in Q. graffini. In addition, in F. paradisi, the hallucal
claw is comparatively more recurved and the penultimate pha-
lanx of digit III is subequal in length to the proximal phalanx
(the proximal phalanx is longest in Q. graffini). The pubis of the
indeterminate Xiagou Formation enantiornithine GSGM-04-
CM-007 is rod-like, and its distal end is curved 90to the proxi-
mal shaft (Lamanna et al., 2006), whereas in Feitianius the pubis
is dorsoventrally compressed and ends in a pubic boot. Unfortu-
nately, there are no overlapping skeletal elements to compare
with Dunhuangia lii Wang et al., 2015, a newly described enan-
tiornithine from Changma (Wang et al., 2015). Compared with
other enantiornithines, the pygostyle is proportionally shorter
than in species of the Longipterygidae, the tarsometatarsus is
considerably more gracile than in all species within the Bohaior-
nithidae or Avisauridae, and the metatarsal and digit I are
shorter than in species of the Pengornithidae. Feitianius paradisi
is most similar to Jehol ‘cathayornithiforms’ such as species of
Cathayornis,Eoenantiornis,Protopteryx, and Sinornis but differs
from these taxa in the detailed anatomy of the pelvic girdle.
DESCRIPTION
Skeletal Anatomy
Axial Skeleton—The caudal-most five thoracic vertebrae are pre-
served in near-complete articulationwitheachotherandthesynsa-
crum (Fig. 1). They are similar to those of other enantiornithines
(Chiappe and Walker, 2002), except that the lateral excavations are
shallow and notably less groove-like. The first preserved vertebra
appears to be slightly craniocaudally shorter than the rest. The para-
pophyses are centrally located, as in other enantiornithines, just cra-
nioventral to the transverse processes. The neural spines are tall
and dorsally expanded both cranially and caudally, such that they
are fan-shaped in lateral view, with longer dorsal than ventral ends.
The vertebrae are amphiplatyan. The ventral surfaces of the cra-
nial-most three thoracic vertebrae each bear a slight groove—this is
absent in the caudal-most two vertebrae, which may indicate that it
is a diagenetic artifact. The articular surfaces of the thoracic verte-
brae are much larger than the vertebral foramen. The synsacrum is
largely obscured by the articulated pelvic girdle; however, the visible
portions are fully fused. The cranial articular surface of the synsa-
crum is flat. The lateral surface is also flat, lacking the pneumatic
fossae (‘pleurocoels’) present in ornithuromorphs (Clarke, 2004).
The synsacrum is dorsoventrally taller at the cranial end, gradually
decreasing in height caudally. A well-developed spinous crest
appears to be present along the entire length of the synsacrum,
slightly decreasing in height caudally.
Five to six articulated free caudal vertebrae are preserved in left
lateral view, revealing tall neural spines that are more than half the
heights of their respective centra. These vertebrae also possess bro-
ken, distolaterally oriented transverse processes. The prezygapophy-
ses are reduced, whereas the postzygapophyses are approximately
one-third the length of the centrum (Fig. 2B). The combined length
of the free caudals slightly exceeds that of the pygostyle, as in some
enantiornithines, whereas the pygostyle is longer in many other
members of the clade (e.g., Iberomesornis romerali Sanz and Bona-
parte, 1992, Longipteryx chaoyangensis Zhang et al., 2000) and
much shorter in others (all species in the Pengornithidae).
The pygostyle is typically enantiornithine in morphology
(Chiappe and Walker, 2002; Chiappe et al., 2002): it is fairly
large and robust, and bears paired ventrolateral processes that
extend the proximal three-fourths of the pygostyle before disap-
pearing distally to form a constriction along the distal one-
fourth; the distal tapered portion is poorly preserved and the tip
is preserved only as an impression (Fig. 2B). The proximal end
of the left ventrolateral process is thick compared with that of
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other known enantiornithines, whereas this process is thin and of
an even thickness throughout in Halimornis thompsoni Chiappe
et al., 2002. This process appears more laterally directed than in
H. thompsoni, such that the pygostyle is dorsolaterally exca-
vated, as in Sinornis santensis Sereno and Rao, 1992. This sug-
gests that the ventral surface was not as deeply concave as in H.
thompsoni but formed a shallow and wide excavation, as in
Rapaxavis pani Morschhauser et al., 2009. The proximodorsal
surface also bears a pair of short, triangular processes (often
described as a ‘dorsal fork’), as in most other enantiornithines,
but only the left process is visible; it cannot be determined if the
proximodorsal fork was continuous with the proximal end of a
dorsal concavity as in Halimornis. Faint but distinguishable rem-
nants of the processes of the incorporated caudal vertebrae are
visible throughout the pygostyle; they are especially clear in the
proximal half. These processes are not as obvious as in the holo-
type of I. romerali, which is regarded as ontogenetically imma-
ture (Sanz and Bonaparte, 1992). Although any such estimate is
inherently tentative, we suggest that nine or 10 vertebrae were
incorporated into the pygostyle.
A single pair of complete thoracic ribs is preserved in associa-
tion with the cranial-most preserved thoracic vertebra; these are
still in articulation with the vertebra but not in situ, having been
dorsally displaced, possibly when the cranial half of the skeleton
was disarticulated and lost (Fig. 1). Additional thoracic rib frag-
ments are clustered near the first preserved thoracic vertebra.
Several disarticulated gastralia are preserved between the pubes
and femora. Three additional gastral elements are preserved,
apparently in articulation, near the cranial margin of the knee
joint. Because they all appear to be from one side of the gastral
basket, a minimum of three pairs of gastralia were present in F.
paradisi, although we suggest that the gastral basket was proba-
bly larger (because it ranges from six to 10 pairs of elements in
known enantiornithines; O’Connor et al., 2015). The free caudal
vertebrae are articulated with large, unfused hemal arches that
are plate-like, approximately twice as long as they are wide, and
bluntly tapered distally.
Appendicular Skeleton—The pelvic girdle elements are
unfused. All are represented, but the ilia are incomplete: only a
fragment of the preacetabular wing of the left ilium is preserved
FIGURE 1. A, photograph and B, line drawing of specimen GSGM-05-CM-004, the holotype of Feitianius paradisi, gen. et sp. nov. Abbreviations:
cv, caudal vertebrae; d, digit; fe, femur; g, gastralia; ha, hemal arches; il, ilium; is, ischium; mpc, medial plantar crest; mtI–IV, metatarsals I–IV; p, pha-
lanx; pb, pubis; py, pygostyle; sn, synsacrum; tb, tibiotarsus; tmt, tarsometatarsus; tr, thoracic ribs; tv, thoracic vertebrae; vl, ventrolateral process; r
and las prefixes denote right and left, respectively. Scale bar equals 10 mm.
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(Fig. 2D). This fragment suggests that the preacetabular wing
was dorsoventrally broad, as in other enantiornithines. A small
cuppedicus fossa appears to excavate the ventral surface cranial
to the acetabulum. The preacetabular wing is laterally concave.
Compared with the ischiadic peduncle, the pubic peduncle is
more robust and projects farther ventrally, as in most other enan-
tiornithines (O’Connor, 2009). The pubic peduncle is not medio-
laterally compressed, in contrast to the compressed and hook-
like pubic peduncles of L. chaoyangensis (Zhang et al., 2001)
and Parabohaiornis martini Wang et al., 2014a.
The pubes are preserved nearly in perfect articulation with the
ilium and ischium; they have been compressed together, such
that the left is in dorsolateral view and the right is in medial
view. The proximal half of each pubic shaft has a lachrymiform
(i.e., teardrop-shaped) cross-section, with the long axis oriented
mediolaterally and the tapered side positioned medially. The
shaft is dorsoventrally compressed and approximately twice as
wide as it is thick, as in Q. graffini. The pubes are more rod-like
in the indeterminate enantiornithine GSGM-04-CM-007. The
pubic shafts become laterally compressed distally, and the distal
one-tenth of the right pubis bears a flange for articulation with
the left pubis. The pubis ends in a dorsally projecting, tapered
boot (Fig. 2C); the extreme dorsal curvature present in the distal
pubis of GSGM-04-CM-007 was clearly absent, whereas in Q.
graffini the distal end of the pubis is bent ventrally as preserved.
The pubic shafts of F. paradisi are weakly curved, such that their
dorsal surfaces are concave, whereas the pubic shafts are straight
in Q. graffini. The pubes are not strongly retroverted, although
we interpret this condition as exaggerated by the disarticulation
of the pelvic girdle and synsacrum. Although visually obfuscated
by their curvature, the ischia are parallel to the pubes, as in
Q. graffini (Ji et al., 2011).
Both ischia are preserved, the left overlapping the right, in lat-
eral and medial views, respectively (Fig. 2A). The ischia are
slightly less than two-thirds the length of the pubes; each is medi-
olaterally thin and plate-like, with a distinct, tab-like, craniodor-
sally directed dorsal process, as in most other enantiornithines
(Chiappe and Walker, 2002). As in Q. graffini and other enan-
tiornithines, the dorsal process is not fused to the postacetabular
wing of the ilium (Ji et al., 2011). The pubic peduncle of the
ischium is broad and much larger than the narrower iliac pedun-
cle; the dorsal process of the ischium is slightly smaller than the
pubic peduncle. The ventral surface of the ischium is weakly con-
cave, such that it curves toward the pubis, similar to the morphol-
ogy in Shenqiornis mengi Wang et al., 2010, whereas this surface
is straighter in Q. graffini. The distal end of the ischium of Feitia-
nius is slightly deflected dorsally, which gives the bone a weakly
sigmoid appearance; the distal tip is also deflected in the gener-
ally straighter ischium of Q. graffini, but such deflection is absent
in S. mengi. This deflection is pronounced in S. santensis, such
that the blade of the ischium is curved dorsally (Sereno et al.,
2002). A blunt, longitudinal lateral ridge is present along the
proximal half of the ischial corpus; this ridge seems to disappear
distally, but its distal half is obscured by breakage. A similar
ridge is present in several ornithuromorphs (e.g., Schizooura lii
Zhou et al., 2012, Yixianornis grabaui Zhou and Zhang, 2001)
and in the enantiornithines Q. graffini and S. santensis; in the lat-
ter two taxa, this ridge is more strongly developed and has
greater lateral projection than in both Feitianius and Early Cre-
taceous ornithuromorphs. This ridge may correspond to the
attachment of the m. puboischiofemoralis lateralis (Hutchinson,
2001). The lateral surface of the ischium is convex proximally
and flat distally, such that the bone becomes more mediolaterally
compressed along its caudal half, similar to the condition in S.
FIGURE 2. Detail photographs of important morphologies preserved in GSGM-05-CM-004. A, ischia; B, caudal vertebrae including pygostyle; C,
distal ends of the pubes; D, right hip. Abbreviations:ac, acetabulum; at, antitrochanter; cf, cuppedicus fossa; dc, distal constriction; dp, dorsal process;
mr, muscle ridge; ns, neural spine; pf, proximal fork; t, transverse process; and as in Figure 1. Scale bars equal 5 mm.
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santensis. The medial surface of the ischium is flat. In Q. graffini,
the lateral ridge for muscle attachment is reduced distally, such
that the caudal half of the ischium has a triangular cross-section,
with the apex formed by the muscle ridge. In Feitianius, by con-
trast, the cross-section of this part of the ischium is flat. Due to
compression, the two ischia are preserved parallel to one
another, as are the pubes; nevertheless, some degree of medial
curvature was surely present in the pubes and also cannot be
ruled out for the ischia. Medially curved ischia are evident in
enantiornithine pelves exposed in dorsal view (e.g., those of
GSGM-07-CM-001 and Concornis).
Both hind limbs are completely preserved. The femur is pro-
portionally longer in the indeterminate enantiornithine GSGM-
04-CM-007, but the relative proportions of the hind limb ele-
ments of Feitianius are similar to those of Q. graffini: the femur
is approximately 20% longer than the tarsometatarsus (femur to
tarsometatarsus length ratio of 1.194 in Feitianius vs. 1.197 in Q.
graffini); the femur to tibiotarsus length ratio is 0.759 (0.755 in
Q. graffini); and the tarsometatarsus to tibiotarsus length ratio is
0.636 (0.630 in Q. graffini). These similar proportions may sug-
gest that the two taxa occupied comparable ecological niches,
which would not be surprising given that they were collected
from the same locality. Unfortunately, neither of the Feitianius
femora reveals additional anatomical information due to break-
age and their articulation with the pelvic girdle. The tibiotarsus
appears to be fully fused. The proximal end of the cranial surface
of the right tibiotarsus is exposed, and it appears to have borne a
low cnemial crest similar to that of Soroavisaurus australis
Chiappe, 1993. This crest does not appear to be as pronounced
as that of Q. graffini. The left tibiotarsus is exposed in caudolat-
eral view. The fibular crest is well developed but short, occupying
approximately one-fifth the length of the tibiotarsus and is
clearly separated from the proximal end of the bone as in other
basal birds. On the proximocaudal surface, the lateral articular
facet and popliteus tuberosity (well developed in species of Pen-
gornithidae and Neornithes) do not seem to be developed, nor is
a flexor fossa present. The fibula is fairly robust along the proxi-
mal one-third of the tibiotarsus; distally, it rapidly becomes
reduced to a splint. Although its distal end is not clear, the fibula
undoubtedly terminated well proximal to the distal tarsals, as in
other ornithothoracines with the exception of pengornithids. We
estimate that the fibula was two-thirds the length of the tibiotar-
sus. Distally, the cartilaginous articular surface of the tibiotarsus
extends weakly onto the caudal surface of the bone, as in Q. graf-
fini (Ji et al., 2011) and other enantiornithines.
Both pedes are preserved. The left tarsometatarsus is pre-
served in dorsolateral view, and the right in plantaromedial view
(Fig. 3). The tarsometatarsus is fused proximally. Distally, the
metatarsals are disarticulated from one another, indicating that
they were ankylosed only proximally. As in other enantiorni-
thines, in dorsal view, metatarsal IV is mediolaterally thinner
than metatarsals II and III (Chiappe and Walker, 2002). The
third metatarsal is the longest, followed by metatarsal IV and
then II, although the latter are nearly subequal in length, as is
typical of basal birds with the notable exceptions of Longipteryx
chaoyangensis and Yungavolucris brevipedalis Chiappe, 1993
(Chiappe, 1993; Zhang et al., 2001). Metatarsal III is more robust
than metatarsal II, as in Q. graffini (Ji et al., 2011). The cranial
surface of metatarsal III is weakly convex proximally but
becomes flatter distally, and is flat along its distal one-fourth. As
in Q. graffini, a tubercle that is inferred to be the attachment site
of the m. tibialis cranialis is located on the dorsal surface of
metatarsal II, one-fifth the length from the proximal end. In the
left tarsometatarsus, the trochleae of metatarsal II and especially
metatarsal IV are preserved plantarly displaced relative to that
of metatarsal III. We interpret this as due to disarticulation of
the distally unfused metatarsals, because metatarsals II and IV
of the right tarsometatarsus do not appear to be plantarly
displaced. In Q. graffini, the trochlea of metatarsal II is similarly
plantarly displaced due to disarticulation. Metatarsal II of Feitia-
nius bears a well-developed medial plantar crest along the
middle one-third of the shaft, which creates and bounds an exca-
vation on the plantar surface of the tarsometatarsus; whereas
only a weak and proximally restricted plantaromedial thickening
is present in Q. graffini. A very weak lateral plantar crest is pres-
ent near the midpoint of metatarsal IV. Both medial and plantar
crests were reported in the indeterminate enantiornithine
FIGURE 3. Detail photograph of the pedes of GSGM-05-CM-004.
Abbreviations:tc, attachment of the m. tibialis cranialis; and as in Figure
1. Scale bar equals 5 mm.
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GSGM-04-CM-007 (Lamanna et al., 2009). No proximal vascu-
lar foramina are apparent, although it appears that a distal fora-
men existed between metatarsals III and IV, but has been
obscured by the plantar displacement of the latter element; this
foramen would clearly have been closed distally by an unfused
contact. The trochleae of metatarsals II and III are ginglymous,
but that of metatarsal IV is reduced to a single condyle, as in
other enantiornithines. Metatarsals II and III have well-devel-
oped pits for the collateral ligaments on the medial and lateral
surfaces of their trochleae. A shallow dorsal trochlear depression
is also present on metatarsal III. The distal margin of metatarsal
II appears to be slightly angled, such that the medial trochlear
ridge is located slightly proximal to the lateral ridge, which is
also comparatively weaker and does not project as strongly in
the plantar direction. A similar morphology is observed in
GSGM-07-CM-001.
The pedal phalangeal formula is 2-3-4-5-x, as in other Meso-
zoic birds. The penultimate phalanges are the longest in each
digit, which in living birds is indicative of arboreality (Hopson,
2001), and among Early Cretaceous enantiornithines has only
been previously documented in R. pani (Morschhauser et al.,
2009). Compared with the indeterminate enantiornithine
GSGM-04-CM-007, the pedal phalanges of Feitianius are more
robust and distally elongate, and the ungual phalanges are more
recurved. Pedal digits II and III are proportionally longer than in
Q. graffini, which, in turn, has proportionally longer digits than
GSGM-04-CM-007.
Metatarsal I articulates on the caudomedial surface of
metatarsal II, but its trochlea angles laterally, such that digit
I is fully reversed as in Q. graffini and other enantiornithines.
Metatarsal I is ‘P’-shaped, with its proximal and distal articu-
lar surfaces nearly perpendicular to each other. Its shaft is
short and its trochlea is relatively long, such that the former
is only slightly longer than the latter (shaft typically longer).
The ungual phalanx is more robust and recurved than that of
the other digits, although it is slightly shorter than the
unguals of digits II and III. The keratinous ungual sheath is
long and relatively straight.
In pedal digit II of Feitianius the penultimate phalanx is nearly
40% longer than the first phalanx (Table 1). The ungual is long
but weakly recurved in order to accommodate the long horny
sheath, which increases the length of the claw by two-thirds. The
non-ungual phalanges of digit II are dorsoplantarly compressed
and mediolaterally wide, such that the proximal articular surface
is more than twice as wide as tall; this morphology is absent in
Q. graffini. The third digit is the most robust in lateral view and
is composed of three phalanges of subequal length; of these, the
second phalanx is marginally the shortest and the penultimate
phalanx is longest. The claw is approximately as long as that of
the second digit. The first phalanx of the fourth digit is the short-
est but also the most robust; the second and third phalanges are
subequal in length. The penultimate phalanx is the longest, as in
the other digits.
Soft Tissues
In addition to the keratinous sheaths of the pedal unguals
described above, specimen GSGM-05-CM-004 preserves an
array of soft tissues in the vicinity of the ventral pelvic ele-
ments, free caudal series, and pygostyle, including a caudal
TABLE 1. Pelvic girdle and hind limb measurements (mm) of published enantiornithines from the Xiagou Formation.
Specimen
Feitianius Qiliania Lamanna et al., 2006
Dimension 05-CM-004 05-CM-006 04-CM-007 07-CM-001
Ilium 16.3* ——16.6z
Acetabulum 1.9 2.5 1.6 —
Pubis 23.4y17.5 22.9 —
Ischium 13.7 11.5* —14.2
Ischium:pubis 0.585 0.657 ——
Femur 27.1 24.3 24.0 26.3z
Femur:pubis 1.158 1.389 1.048 —
Tibiotarsus 35.7 32.2 29.2y34.4z
Femur:tibiotarsus 0.759 0.755 0.822 0.765
Fibula 14.9* ———
Tarsometatarsus 22.7 20.3 20.3 21.6
Tmt:Tbt 0.636 0.630 —0.628
Femur:Tmt 1.194 1.197 —1.218
Metatarsal I 4.7 3.2 3.1* 5.4y
Metatarsal II 20.5y19.2 19.6 20.4
Metatarsal III 22.7 20.3 20.3 21.6
Metatarsal IV 21.3 —19.1 20.8z
Pedal phalanx I-1 5.1 4.2 4.3 5.4z
Pedal phalanx I-2 5.5y4.4 3.9y5.2
Pedal phalanx II-1 4.5 3.7 3.6 4.7
Pedal phalanx II-2 6.2 4.8 4.9 5.8z
Pedal phalanx II-3 5.0y4.9 4.4 5.9
Pedal phalanx III-1 6.3z4.6 4.8 5.9z
Pedal phalanx III-2 5.5z4.0 4.0 5.3
Pedal phalanx III-3 6.2 4.2 5.0 5.9
Pedal phalanx III-4 6.0y5.8 4.4 5.8z
Combined digit III:mt III 1.057 0.916 0.897 1.060
Pedal phalanx IV-1 3.2z—2.8 3.4
Pedal phalanx IV-2 2.8z2.3 2.0 2.7
Pedal phalanx IV-3 3.1z2.4 2.2 3.1
Pedal phalanx IV-4 4.7 2.8 3.7 4.3
Pedal phalanx IV-5 5.5y4.4 4.7y5.1y
Measurements are for proximodistal lengths, unless otherwise indicated. Dagger symbol (y) indicates estimated lengths; double-dagger (z) indicates
measurements averaged from the right and left; asterisk (*) indicates incomplete elements, preserved lengths.
O’Connor et al.—New enantiornithine Feitianius (e1054035-6)
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plumage that was previously unknown among Mesozoic birds
(Fig. 4). Although the specimen only preserves feathers from
the caudal and caudoventral regions of the body, several dis-
tinct morphologies are evident in these areas. Unfortunately,
the overall preservation of the feathers of Feitianius is poor,
and although multiple varieties of differing sizes can be iden-
tified, the morphological details of each are difficult to ascer-
tain. Attempts to interpret these preserved soft tissues are
further complicated by the frequent overlap of the feathers
with each other and with other tissues. Short body covert
feathers are preserved ventrally, between the pubes and hind
limbs, sometimes overlapping with band-like soft tissue struc-
tures that are clearly preserved only within the soft tissue
outline of the body. We tentatively interpret the latter struc-
tures as internal soft tissues, possibly bands of collagen, but
this identification is equivocal. Similar bands are present in a
referred specimen of the confuciusornithiform Eoconfuciusor-
nis zhengi Zhang et al., 2008 (STM7-144; J.K.O’C., pers.
observ.). As in the referred specimen of E. zhengi, the bands
in Feitianius are of equal length (7–8 mm) and thickness
(approximately 0.5 mm) and are oriented largely parallel to
each other and roughly perpendicular to the body outline
(Fig. 4). A dark organic residue that gradually decreases in
dorsoventral thickness distally extends from the last caudal
vertebrae past the distal margin of the pygostyle (Fig. 4); the
dorsal margin of this mass is straighter and much thinner
over the pygostyle than the ventral margin. We interpret this
as the carbonized remnant of the ‘pope’s nose,’ the soft tissue
that surrounds the pygostyle, including the rectricial bulb
muscles and oil glands (Gill, 2007).
Down-like covert feathers delineate the caudal and caudoven-
tral margins of the body, extending caudally from the vicinity of
the distal end of the pubis, but not reaching the level of the distal
margin of the pygostyle; beyond this point, the coverts are either
pressed against the body or not preserved. They are approxi-
mately 7 mm in length in the pelvic region, increasing to roughly
12 mm along the dorsal surface. These coverts extend caudally
along the dorsal margin of the caudal skeleton, but in this region
their details are obscured by overlap with more elongate feathers
of varying morphologies that project caudally and caudodorsally
from the pygostyle. One ventral-most covert, preserved level
with the distal half of the pygostyle and not obscured by overlap,
appears to be pennaceous; short barbs are preserved angled
towards a narrow rachis (Fig. 4C).
The tail plumage itself is composed of a large number of rectri-
ces of varying lengths and morphologies (Fig. 4A, B). We esti-
mate that a minimum of 12 rectrices were present; however,
their suboptimal preservation, substantial overlap, and consider-
able morphological variation preclude a definitive assessment in
this regard. Two distinct morphotypes may be differentiated
most readily by length, whereas a third type is most easily distin-
guished by its morphology. Although distally incomplete, the
longer of the former two rectricial morphotypes (here termed
‘morphotype A’ for ease of description) are at least 40–45 mm in
length, whereas the shorter feathers (‘morphotype B’) are
approximately 18 mm long. Although a rachis is not evident in
any of these feathers, we interpret this as a taphonomic artifact;
vanes are clearly preserved in some, and as such, we consider all
of these feathers to be pennaceous. Whereas most of these rectri-
ces appear to project from the dorsal margin of the distal-most
free caudals and pygostyle, one or two others seem to originate
directly from the distal margin of the latter element.
Approximately five to seven feathers of ‘morphotype A’ are
present. We interpret these as being exposed primarily in lateral
view, with only the rachis and lateral vane visible. Thus, we can-
not determine if these feathers were asymmetrical. The darker
color of the upper margins of these feathers as preserved is
thought to be a consequence of overlap with the medial vane.
Barbs only appear to be present along the distal 55% of each of
these rectrices. These barbs meet the rachis at an angle of
approximately 15and become more elongate distally. The
‘morphotype A’ feathers are curved, such that their dorsal mar-
gins are convex.
At least five of the shorter, smaller ‘morphotype B’ feathers
are unquestionably preserved, with more almost certainly pres-
ent but obscured by overlap with other feathers. ‘Morphotype B’
feathers are approximately one-half the length and distal width
of their ‘morphotype A’ counterparts, at least as the latter are
preserved; however, because most of these longer feathers are
distally incomplete, they likely were considerably more than
twice the length of the ‘morphotype B’ feathers in life. All
‘morphotype B’ feathers taper distally. They do not present clear
evidence for either a rachis or barbs; several of them, however,
preserve a dark longitudinal line that we interpret as the rachis.
The presence of this structure, coupled with the lengths of these
feathers, strongly suggests that they are pennaceous. The appear-
ance of the several ‘morphotype B’ feathers preserved in lateral
view suggests that they are curved, such that their dorsal surfaces
are convex, although to a lesser degree than in ‘morphotype A.’
In ‘morphotype B,’ the vane appears to maintain an even thick-
ness and to extend along most of the length of the feather rather
than being restricted to its distal preserved half as in
‘morphotype A.’
Rachis-dominated feathers similar to those preserved in the
holotypic specimen of P. fengningensis are also present in
GSGM-05-CM-004 (‘morphotype C’). Similar to the condi-
tions in the holotypes of P. fengningensis and B. guoi, only
the proximal portions of the ‘morphotype C’ feathers are pre-
served in Feitianius, so their total lengths and the morpholo-
gies of their distal ends cannot be determined. In GSGM-05-
CM-004, the rachis-dominant feather(s) is preserved as a sin-
gle straight swath of organic carbon projecting directly dis-
tally from the pygostyle. The feather lacks any evidence of
barbs, but the wide rachis is longitudinally ‘striped’ and bears
a narrow strip of undifferentiated vane visible on the dorsally
preserved margin, as in the rachis-dominated ‘racket-plume’
rectrices (i.e., ‘elongate ribbon-like tail feathers’ of Zhang
et al., 2006) of other enantiornithines (e.g., the holotype
specimens of B. guoi,D. sentisorhinus,P. gracilis,P. fengnin-
gensis), and confuciusornithiforms (O’Connor et al., 2012). A
wide, dark carbonized trace of equal thickness is present ven-
trally. This structure preserves no discernible features such as
barbs, rendering it difficult to interpret. It may represent the
lateral or medial vane, multiple overlapping feathers, or
both. However, the even thickness of this carbonized struc-
ture suggests that it might correspond to a wide medial vane.
Similar rachis-dominated feathers are preserved in the holo-
type of Eopengornis martini Wang et al., 2014b, in which the
tail is formed by a pair of elongate, fully pennaceous feathers
with a wide medial vane (the width of which is greater than
thewidthofthetrailingedgevaneintheremiges)andanar-
row lateral vane, both of which maintain a fairly even thick-
ness throughout the full proximodistal length of the feather
(Wang et al., 2014b).
PHYLOGENETIC ANALYSIS
We conducted a phylogenetic analysis to elucidate the rela-
tionships of Feitianius to other enantiornithine birds. We mod-
ified the data matrix of O’Connor and Zhou (2013) to include
Feitianius as well as all other published enantiornithine taxa
(except the recently described Dunhuangia lii) and specimens
from the Xiagou Formation of the Changma locality (a total
of six additional operational taxonomic units; Qiliania,
GSGM-02-0901, GSGM-04-CM-007, GSGM-04-CM-023, and
GSGM-07-CM-001) (You et al., 2005; Harris et al., 2006;
O’Connor et al.—New enantiornithine Feitianius (e1054035-7)
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FIGURE 4. Detail images of the caudal plumage of GSGM-05-CM-004. A, photograph; B, interpretive drawing; C, detail of the pennaceous covert;
D, photograph of one of the ‘racket plumes’ preserved in GSGM-07-CM-001. Abbreviations:A, morphotype ‘A’; B, morphotype ‘B’; C, morphotype
‘C’; ms, medial stripe; rd, rachis in ‘rachis-dominated’ feathers; sbr, soft body residue. Scale bar equals 10 mm.
O’Connor et al.—New enantiornithine Feitianius (e1054035-8)
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Lamanna et al., 2006; Ji et al., 2011; O’Connor et al., 2012).
We also removed Zhongornis haoae Gao et al., 2008, from the
analysis because we consider this taxon to be a non-avian the-
ropod (specifically, a scansoriopterygid) rather than a bird
(O’Connor and Sullivan, 2014; You, 2014). The updated data
set consists of 64 taxa scored for 245 morphological characters
(see Supplemental Data). We analyzed the data set using
TNT (Goloboff et al., 2008). We first conducted a traditional
(heuristic) search using the tree-bisection reconnection (TBR)
swapping algorithm, retaining the single shortest tree of 1000
trees. This produced a well-resolved topology with a length of
834 steps. A second round of TBR yielded 312 most parsimo-
nious trees (MPTs), also of 834 steps, the strict consensus of
which places all Changma enantiornithines within a basal
polytomy that also includes Elsornis keni Chiappe et al., 2006,
and Protopteryx fengningensis, taxa that are consistently
recovered at the base of Enantiornithes. This polytomy also
includes the ‘longipterygid’ enantiornithines Boluochia zhengi
Zhou, 1995, Longipteryx chaoyangensis,andRapaxavis pani,
the bohaiornithid Shenqiornis mengi, and the probable orni-
thuromorph Chaoyangia beishanensis Hou and Zhang, 1993
(O’Connor and Zhou, 2013). Like most of the Changma enan-
tiornithines, C. beishanensis is known only from a single par-
tial skeleton, and probably as a consequence, the
hypothesized phylogenetic position of this taxon has varied
widely in the literature (Zhou, 1999; Clarke and Norell, 2002).
Although C. beishanensis has recently been shown to be a
basal ornithuromorph (O’Connor and Zhou, 2013), this con-
clusion is only weakly supported by cladistic analysis. When
its phylogenetic relationships have been analyzed, the taxon
has commonly fluctuated between the two ornithothoracine
clades (Enantiornithes and Ornithuromorpha); indeed, some
recent analyses have removed C. beishanensis to generate a
reduced strict consensus tree (O’Connor and Zhou, 2013).
The equal-length MPTs generated by the present analysis
vary considerably in the positions of taxa within the basal enan-
tiornithine polytomy of the strict consensus tree. For example,
the isolated pectoral limb GSGM-04-CM-023 (Harris et al.,
2006) is resolved both in a basal-most position (as in the results
from the first round of TBR) as well as in the most derived posi-
tion. This lack of topological stability indicates that these rela-
tionships are not supported by character data (i.e., they are
zero-length nodes).
One noteworthy aspect of our phylogenetic results is that all
enantiornithines from the Xiagou Formation are resolved in a
polytomy with the most basal known members of this clade. By
contrast, Gansus yumenensis—the numerically dominant Xiagou
bird—is considered a fairly advanced ornithuromorph, typically
resolved in a position more derived than any taxon from the
penecontemporaneous Jehol Biota of northeastern China (You
et al., 2006; O’Connor et al., 2010; O’Connor and Zhou, 2013;
Wang et al., 2014a). The other known Xiagou ornithuromorph
taxa—Changmaornis houi Wang et al., 2013, Yumenornis huangi
Wang et al., 2013, and Jiuquanornis niui Wang et al.,
2013—appear to occupy less derived positions in the clade; in
particular, the latter taxon shares an archaic sternal morphology
with the very basal ornithuromorph Archaeorhynchus spathula
Zhou and Zhang, 2006, suggesting a close relationship (You
et al., 2010; Wang et al., 2013). Therefore, although not strictly
revealed as such in the cladogram, it appears that the Xiagou
ornithuromorphs may have occupied a much broader phyloge-
netic spectrum than did the enantiornithines from this formation.
DISCUSSION
Represented by specimen GSGM-05-CM-004, the new taxon
Feitianius paradisi, gen. et sp. nov., greatly increases the diversity
of recognized tail morphologies within Enantiornithes. Even
prior to this discovery, enantiornithines preserved a greater
diversity of caudal plumages than any other Cretaceous avian
clade. Several specimens (e.g., Dapingfangornis sentisorhinus
LPM B00027, GSGM-07-CM-001) possess elongate, paired,
rachis-dominated ‘racket plumes’ that vary substantially in mor-
phology and length between taxa (O’Connor et al., 2012). Unfor-
tunately, these feathers are distally incomplete in the majority of
the specimens in which they are preserved, e.g., Bohaiornis guoi
LPM B00167, Protopteryx fengningensis IVPP V11665, DNHM
D2884 1/2 (Zhang et al., 2000; Hu et al., 2011), and some speci-
mens (e.g., Eopengornis martini STM24-1) possesses rachis-dom-
inated ‘streamers’ (Wang et al., 2014b). Other specimens (e.g.,
Eoenantiornis buhleri Hou et al., 1999, IVPP V11537, STM29-8)
possess no rectrices, only morphologically simple body coverts
surrounding the pygostyle (O’Connor, 2009; O’Connor et al.,
2012). One taxon, (Paraprotopteryx gracilis STMV001, (Zheng
et al., 2007) reportedly possesses four rachis-dominated ‘racket-
plumes,’ and the holotype of Shanweiniao cooperorum
O’Connor et al., 2009 (DNHM D1878 1/2), preserves impres-
sions of portions of at least four closely arranged tail feathers
that may potentially have formed an aerodynamic surface
(O’Connor et al., 2009). In contrast, several Jehol ornithuro-
morphs (e.g., Hongshanornis longicresta Zhou and Zhang, 2005,
Piscivoravis lii Zhou et al., 2013, Yanornis martini Zhou and
Zhang, 2001, Yixianornis grabaui; Zhou and Zhang, 2005; Clarke
et al., 2006; Zhou et al., 2013) preserve large, round tails formed
by a fan of 6–10 rectrices, and one taxon (Schizooura lii) has a
forked tail (Zhou et al., 2012), all considered aerodynamic mor-
phologies. The only exception is the holotype of the recently dis-
covered ornithuromorph Iteravis huchzermeyeri Zhou et al.,
2014, which preserves what appears to be a pair of short, orna-
mental rectrices (Zhou et al., 2014). With the possible exception
of those preserved in the holotype specimen of Shanweiniao
cooperorum, all preserved enantiornithine rectricial morpholo-
gies are interpreted as having ornamental functions, strongly sug-
gesting that sexual selection was a major driving force in shaping
tail morphologies within the clade (Wang et al., 2014b).
Unlike the feathers that comprise the wing, those of the tail
are not essential for flight in extant birds (Thomas, 1993).
Although most extant birds have aerodynamic caudal morpholo-
gies, the tail is the most commonly modified part of the plumage
and modifications of the tail feathers are most frequently related
to ornamentation (Stettenheim, 2000). Exaggerated feather
shapes and lengths may be readily identified as sexually driven
traits in living birds (Andersson, 1982; Balmford et al., 1993;
Fitzpatrick, 1998). The elongate ‘streamers’ of Eopengornis mar-
tini and the ‘racket plumes’ in species of the Confuciusornithi-
formes, GSGM-07-CM-001, and other enantiornithines are thus
interpreted as ornaments (O’Connor et al., 2013; Wang et al.,
2014b). The ornamental feathers of these Early Cretaceous birds
are unusual in that they are rachis-dominated, which is an extinct
morphotype (Zhang and Zhou, 2000; O’Connor et al., 2012).
The preserved carbonized residue of what appears to be a wide,
medially striped rachis directed toward the pygostyle strongly
suggests that GSGM-05-CM-004 possessed a similar pair of elon-
gate ornamental rectrices (Fig. 4). Paired, elongate tail feathers
are present in many modern birds, both sexually dimorphic and
non-dimorphic species, and are typically associated with a short,
aerodynamic rectricial fan (e.g., species in the Momotidae—both
genders; Dicrurus paradiseus, the greater racket-tailed dron-
go—both genders; Trochilus polytmus, the red-billed streamer-
tail—males only; Ocreatus underwoodii, the booted racket-
tail—males only). Avian plumage is under multiple selective
pressures; therefore, such a tail morphology serves both aerody-
namic and ornamental functions (Thomas, 1997).
Despite the diversity of recognized caudal plumages, the over-
whelming majority of previously described Mesozoic birds have
a tail composed of only one rectricial morphotype. The sole
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exception in this regard is the long-bony-tailed bird Jeholornis,
species of which have an autapomorphic ‘two-tailed’ morphol-
ogy, in which the rectrices in the proximal fan and the distal
frond differ from one another in size and morphology, and col-
lectively serve both aerodynamic and ornamental functions
(O’Connor et al., 2013). By contrast, no Early Cretaceous bird
with paired ornamental feathers (e.g., Confuciusornis, enantior-
nithines) also possesses an aerodynamic tail fan. Specimen
GSGM-05-CM-004 is the first Mesozoic bird to preserve rachis-
dominated feathers along with additional types of rectrices. Nev-
ertheless, these shorter rectrices (designated ‘morphotype A’
and ‘morphotype B’) appear to have different orientations from
the body relative to one another, suggesting that they did not
form a cohesive, lift-forming surface. Their degree of dorsal cur-
vature further indicates that these feathers probably did not
serve an aerodynamic purpose. The three rectricial morphotypes
preserved in the holotype of Feitianius, none of which appears to
be aerodynamic, suggest that the tail plumage of this bird may
be interpreted as entirely ornamental and driven by sexual selec-
tion, with minimal visible effects of natural selection on its mor-
phology (Balmford et al., 1993). The considerable differences in
morphology between these morphotypes suggest a very elabo-
rate caudal plumage in the new Xiagou enantiornithine.
Among extant birds, extreme ornaments consisting of multiple
rectricial types are usually limited to males of sexually dimorphic
species because of the associated ‘costs’ of such feathers: these
ornaments often decrease aerodynamic efficiency and increase
conspicuity, and also require energy to grow and maintain
(Thomas, 1993; Fitzpatrick, 1999). Limited by their energetic
investment in reproduction, female birds—even those of species
with mutual ornamentation or reverse sexual dimorphism—
never reach the extremes of ornamentation observed in polyga-
mous males with little to no parental responsibility (Winquist
and Lemon, 1994; Cuervo and Møller, 2000). Among living birds,
elaborate tail plumages formed by several types of non-aerody-
namic rectrices that vary in length and morphology (and also
color) are primarily associated with males of sexually dimorphic
species. The prime example here is birds of paradise (Passeri-
formes: Paradisieidae) such as the greater bird-of-paradise
(Paradisaea apoda) and Princess Stephanie’s astrapia (Astrapia
stephaniae), but other examples include male chickens (cocks)
and pheasants (Galliformes: Phasianidae), the lyrebird Menura
spp. (Passeriformes), and some species of ducks (Anseriformes:
Anatidae). These ornaments are used primarily to attract mates,
serving as an indicator of fitness because of the difficulty in main-
taining such structures (Thomas, 1997; Cuervo and Møller, 2000).
Ornamental rectrices are additionally used to signal between
competing males. In Neornithes, reverse sexual dimorphism is
most often expressed in size (e.g., raptorial birds) and is usually
related to resource acquisition (Tobias et al., 2012). In the rare
cases where the female of the species has the more attractive
plumage (e.g., the paradise shelduck Tadorna variegata), this
does not approach the degree of elaboration present in male
dimorphic plumages and is more commonly associated with sex-
ual dichromatism.
The paired ‘racket plumes’ originally described in Confuciusor-
nis have been suggested to represent a sexually dimorphic feature
(Feduccia, 1996). Although similar feathers are present in extant
species of both non-dimorphic and sexually dimorphic birds, the
paired rachis-dominated ‘racket plumes’ are clearly absent in
some confuciusornithiform specimens, despite their excellent
feather preservation (Hou et al., 1996; Chiappe et al., 1999,
2008). Alternatively, specimens that clearly lack elongate feathers
could conceivably represent molting individuals. Although there
are not yet enough known specimens of any one taxon to defini-
tively evaluate this hypothesis, these feathers are similarly inter-
preted as sexually dimorphic in the enantiornithine species
in which they occur (Zheng et al., 2007). In the single
Confuciusornis specimen and in the one indeterminate enantior-
nithine in which the gender can be confidently identified as female
(due to the preservation of medullary bone and ovarian follicles,
respectively), elongate rectrices are clearly absent, supporting the
hypothesis that these feathers are only present in males of these
species (Chinsamy et al., 2013; O’Connor et al., 2014).
The tail morphology of Feitianius strongly resembles that of
males in modern sexually dimorphic species with hyperexagger-
ated ornamental rectricial displays (e.g., the greater bird-of-para-
dise Paradisaea apoda). Together, the three caudal feather
morphotypes of the new Xiagou enantiornithine would have
formed a visually impressive but energetically costly display, pre-
sumably intended for intraspecific signaling. Multiple specimens
are typically required to establish the existence of sexual dimor-
phism in a species. However, based on observations of extant
birds (Thomas, 1997), and the exaggerated nature of the rectri-
cial morphology of the holotype of Feitianius paradisi versus that
of all other enantiornithines, we suggest that this species had sex-
ually dimorphic plumage and that the holotype pertains to an
adult male, despite the fact that the taxon is currently known
from only this specimen.
The grade of complexity of the ornamental tail feathers
provides indirect evidence of behavior in Feitianius.The
degree of elaboration may indicate that this enantiornithine
was socially polygamous, given that these types of birds tend
to have a greater degree of caudal dimorphism than monoga-
mous birds (Bj€
orklund, 1990) and hypertrophied ornaments
are most commonly observed in polygamous neornithines. It
also suggests limited paternal care of offspring in Feitianius
(Winquist and Lemon, 1994; Cuervo and Møller, 2000). The
level of elaboration of the caudal plumage further suggests
that Feitianius did not fly often, at great speeds, and/or for
long distances, suggesting that it inhabited a densely forested
environment (similar to the habitats of extant quetzals, Phar-
omachrus and Euptiolotis spp.) (Thomas, 1997); this is consis-
tent with the arboreal ecologies inferred for enantiornithines
based on their pedal morphology (Morschhauser et al., 2009;
O’Connor, 2009) and is also consistent with the abundance of
fossil coniferous trees collected at Changma (M.L., pers.
observ.). Among modern birds, the most elaborate tail mor-
phologies are phylogenetically derived (Gluckman, 2014);
however, Feitianius falls within the large polytomy of basal
enantiornithines (Fig. 5), which may suggest that this clade
began to experiment with different plumages fairly early in
its diversification. As in many modern taxa, there is a strong
possibility that the different feather morphotypes varied in
color as well: elaborate tail displays are often associated with
bright colors, iridescence, and/or visual patterns such as
stripes. Regrettably, a varnish applied after preparation
makes it impossible to evaluate the feathers of GSGM-05-
CM-004 for preserved melanosomes.
The unique tail plumage of Feitianius reveals an even
greater level of complexity in this part of the integument than
was previously recognized and indicates that enantiornithines
evolved complex, non-aerodynamic caudal morphologies
formed by multiple rectrix types, presumably to form elabo-
rate displays, in parallel to those documented in Neornithes.
The diversification of Enantiornithes during the Cretaceous is
considered the first major avian radiation (Chiappe, 1995b).
Although currently enantiornithines do not approach the skel-
etal diversity encompassed within Neornithes (O’Connor and
Chiappe, 2011), the new specimen suggests that the caudal
plumages of these archaic birds may have reached levels of
complexity comparable to those of extant taxa. This is unsur-
prising considering a recent study that suggested that plumage
is highly evolutionarily labile, as inferred from the number of
times that exaggerated features have independently evolved
among closely related modern birds (Gluckman, 2014). The
O’Connor et al.—New enantiornithine Feitianius (e1054035-10)
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diversity of ornamental tail morphologies within Enantior-
nithes, which more closely approaches modern complexity and
diversity than does the morphology of the skeleton, strongly
suggests that sexual selection was a major driver of the diver-
sification of feather and plumage morphologies during the
early evolution of Aves.
Body Coverts in Basal Birds
Notably, the holotype of Feitianius preserves evidence of pen-
naceous coverts, which are not observed in Jehol Biota enantior-
nithine taxa despite the fact that a large number of specimens of
these birds preserve feathers (O’Connor, 2009; O’Connor et al.,
2012). In Jehol enantiornithines such as the holotype specimens
of Longipteryx chaoyangensis and Protopteryx fengningensis, the
body feathers appear to be non-shafted (as defined by Zhang
et al., 2006). Although these feathers are inferred to have func-
tioned as body contour feathers, they superficially resemble the
down feathers of modern birds; they differ in that they do not
radiate from a short rachis, but rather seem to consist of proxi-
mally undifferentiated vanes that fray into individual barbs dis-
tally, a now-extinct feather morphotype (Zhang et al., 2006;
O’Connor et al., 2012). By contrast, at least one small covert
feather of GSGM-05-CM-004 clearly preserves a herringbone
structure and a rachis (Fig. 4C). Pennaceous covert feathers
have also been reported in Archaeopteryx (Foth et al., 2014).
The absence of pennaceous feathers in enantiornithines and
other basal birds (e.g., Confuciusornis,Jeholornis) from the
Jehol Group is seemingly at odds with their phylogenetic place-
ment as more derived than Archaeopteryx (Fig. 5). However, the
vast number of specimens of these birds challenges any purely
taphonomic explanation for this difference in observed feather
morphology, and some well-preserved feathers of Jehol avians
were clearly non-shafted (Zhang et al., 2006; O’Connor, 2009;
O’Connor et al., 2012).
Most feathers of the Feitianius holotype GSGM-05-CM-004 do
not preserve clear evidence that they were vaned, but instead
appear wispy, similar to those of Jehol birds. Nevertheless, vanes
may be observed in some regions of the large ‘morphotype A’
feathers and in a single ventral covert. This suggests that all
feather morphotypes of this enantiornithine were pennaceous,
but that this has subsequently been obscured by taphonomic pro-
cesses. No clearly non-shafted feathers are visible in GSGM-05-
CM-004. These non-shafted body coverts have so far been docu-
mented only in birds from the Jehol ecosystem, for which evi-
dence indicates a fairly cold climate (Amiot et al., 2011).
Plumaceous down feathers are considered derived within Neo-
rnithes (Stettenheim, 2000); as such, we hypothesize that the
non-shafted morphology may also be derived and that basal
Jehol birds evolved morphologically comparable non-shafted
coverts for insulation from their cold environment.
ACKNOWLEDGMENTS
We thank the personnel of the former Fossil Research and
Development Center of the Third Geology and Mineral Resour-
ces Exploration Academy of Gansu Province for discovering and
preparing the specimen. We are grateful to J. Zhang (Institute of
Vertebrate Paleontology and Paleoanthropology) for photo-
graphing the specimen and C. Crist (Carnegie Museum of Natu-
ral History) for the line drawing in Figure 1B. The manuscript
was improved by constructive reviews from two anonymous
reviewers and editorial comments from T. Worthy. This research
was supported by the National Basic Research Program of China
(973 Program, 2012CB821906), the National Natural Science
Foundation of China, the Hundred Talents Project of the Chi-
nese Academy of Sciences, the Gansu Provincial Bureau of Geo-
Exploration and Mineral Development, and the Carnegie
Museum of Natural History.
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Submitted October 27, 2014; revisions received April 9, 2015; accepted
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Handling editor: Trevor Worthy.
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