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New material of Chaoyangopterus (Pterosauria: Pterodactyloidea) from the Early Cretaceous Jiufotang Formation of western Liaoning, China

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A new edentulous pterosaur from the Yuanjiawa beds of the Early Cretaceous Jiufotang Formation in Yuanjiawa, Chaoyang, western Liaoning, China, is described. The fossil, an incomplete and scattered skeleton, including partial skull and lower jaws, is identified as Chaoyangopterus zhangi, based on similar proportions of the limb bones. The specimen shows that Chaoyangopterus possessed moderately elongate mid-cervical vertebrae with low, blade-like neural spines and lacked lateral pneumatic foramina. This discovery not only further supports a distinct Chaoyangopteridae within the Azhdarchoidea, but also provides a new scope for reviewing the evolution of the family Azhdarchidae.
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New material of Chaoyangopterus (Pterosauria:
Pterodactyloidea) from the Early Cretaceous Jiufotang Formation
of western Liaoning, China
Chang-Fu Zhou, Shenyang
With 4 figures and 1 table
Z
HOU
, C.-F. (2010): New material of Chaoyangopterus (Pterosauria: Pterodactyloidea) from the
Early Cretaceous Jiufotang Formation of western Liaoning, China. – N. Jb. Geol. Paläont. Abh.,
257: 341– 350; Stuttgart.
Abstract: A new edentulous pterosaur from the Yuanjiawa beds of the Early Cretaceous Jiufotang
Formation in Yuanjiawa, Chaoyang, western Liaoning, China, is described. The fossil, an incomplete
and scattered skeleton, including partial skull and lower jaws, is identified as Chaoyangopterus
zhangi, based on similar proportions of the limb bones. The specimen shows that Chaoyangopterus
possessed moderately elongate mid-cervical vertebrae with low, blade-like neural spines and lacked
lateral pneumatic foramina. This discovery not only further supports a distinct Chaoyangopteridae
within the Azhdarchoidea, but also provides a new scope for reviewing the evolution of the family
Azhdarchidae.
Key words: Pterosauria, Pterodactyloidea, Azhdarchoidea, Chaoyangopterus, Early Cretaceous,
Jiufotang Formation, western Liaoning.
1. Introduction
Pterosaurs, along with feathered dinosaurs, basal
birds, and mammals, flourished in the Jehol Biota
during the Early Cretaceous of western Liaoning
Province and adjacent areas of northeastern China.
Until now, 26 nominal species of pterosaurs have been
reported from the Jehol Group, including both basal
pterosaurs and pterodactyloids (A
NDRES
& J
I
2008;
L
Ü
et al. 2006a, 2007, 2008; W
ANG
et al. 2007, 2008a,
b). Apart from the anurognathid Dendrorhynchoides
curvidentatus J
I
& J
I
, 1998, pterodactyloid pterosaurs
dominated the Jehol Biota with 25 taxa, representing
a significant diversity of pterosaurs in Cretaceous
terrestrial ecosystems (W
ANG
et al. 2005).
Recently, 11 edentulous pterosaur taxa have been
named, including the tapejarids Sinopterus dongi
W
ANG
& Z
HOU
, 2003, Sinopterus gui L
I
et al., 2003,
Huaxiapterus jii L
Ü
& Y
UAN
, 2005, Huaxiapterus
corollatus L
Ü
et al., 2006b, and Huaxiapterus ben-
xiensis L
Ü
et al. 2007, having a deep snout and
dentary crest; and the possible azhdarchoids Chao -
yangopterus zhangi W
ANG
& Z
HOU
, 2003, Jidapterus
edentus D
ONG
et al., 2003, Eopteranodon lii L
Ü
&
Z
HANG
, 2005, Eoazhdarcho liaoxiensis L
Ü
& J
I
, 2005,
Nemicolopterus crypticus W
ANG
et al., 2008b, and
Shenzhoupterus chaoyangensis L
Ü
et al., 2008, having
a low and strongly elongate snout and lower jaws. Of
these azhdarchoids, Nemicolopterus crypticus is a tiny
pterosaur apparently specialized for an arboreal
© 2010 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de
DOI: 10.1127/0077-7749/2010/0081 0077-7749/2010/0081 $ 2.50
N. Jb. Geol. Paläont. Abh. 257/3, 341– 350 Article
published online June 2010
342 Chang-Fu Zhou
forest-dwelling lifestyle(W
ANG
et al.2008b). However,
the other five taxa are similar to each other, having
a long and low skull and lower jaws, but are clearly
different from the Chinese tapejarids (Sinopterus
and Huaxiapterus). Except for the recently-erected
Shenzhoupterus, the other four azhdarchoid taxa were
thought to be synonymous with Chaoyangopterus and
were included within the Pteranodontidae by W
ANG
&
Z
HOU
(2006), but L
Ü
& J
I
(2006), L
Ü
et al. (2006a),
A
NDRES
& J
I
(2008), and L
Ü
et al. (2008) disputed a
pteranodontid affinity. Consequently, L
Ü
et al. (2008)
erected Chaoyangopteridae to include the five taxa,
and assigned it to the Azhdarchoidea on the basis
of several characters: relatively large nasoantorbital
fenestra; relatively short wing-finger, elongate first
wing phalanx; and relatively long hindlimb. In ad -
dition, the recently described Lacusovagus magni -
ficens from the Early Cretaceous (?Aptian) of Brazil
has been referred to the Chaoyangopteridae, implying
a wide geographical distribution for this group
(W
ITTON
2008). Thus chaoyangopterids perhaps
represent an early radiation of long-snouted and
edentulous azhdarchoid pterosaurs in the Early Creta-
ceous.
The present study describes a new specimen of
Chaoyangopterus collected from the Early Cretaceous
Jiufotang Formation in Yuanjiawa Village, Daping-
fang, Chaoyang City, western Liaoning Province in
2005. Resembling the above five taxa, this specimen
has a long and low skull and lower jaws, and adds
further insight into the anatomy of these edentulous
pterosaurs. The specimen is identified as Chaoyang-
opterus zhangi based on similar proportions of the
limbs. This discovery of the specimen described here
not only provides new knowledge of the anatomy of
Chaoyangopterus, but also provides important in -
sights on the evolution of the Azhdarchoidea.
2. Geological setting
In 2004 and 2005, the Paleontological Institute of
Shenyang Normal University undertook a field col -
lecting program in western Liaoning. The two-
year program resulted in the collection of hundreds
of vertebrate fossils, including specimens of the
feathered dinosaur Microraptor, the birds Jeholornis,
Confuciusornis, Dapingfangornis, and Alethoala -
ornis, the pterosaurs Longchengopterus and Chao -
yangopterus, and aquatic reptiles, including turtles
and choristoderes (D
UAN
et al. 2006; L
I
et al. 2006,
2007; L. W
ANG
et al. 2006). The fossil locality
(41°34’20”N, 120°09’30”E; Fig. 1) is situated on a
hill near Yuanjiawa Village, Dapingfang, Chaoyang
City, western Liaoning Province. The fossil-bearing
layer occurs within the Yuanjiawa beds of the Early
Cretaceous (Aptian) Jiufotang Formation (H
E
et al.
Fig. 1. (A) Locality map showing the fossil site (asterisk; 41°34’20”N, 120°09’30”E) of Yuanjiawa Village, Dapingfang,
Chaoyang City, western Liaoning Province, Northeast China. (B) Photo of outcrop in the fossil site of Yuanjiawa Village.
Arrows point the three brown-yellow marl layers, by numbered as I-III.
2004), which is a lacustrine unit consisting mainly of
dark-gray mudstone, shale, and sandstone with three
brown-yellow marl layers (D
UAN
et al. 2006; Fig. 2).
The pterosaur fossil described here is from a layer
2.1 m below the second brown-yellow marl layer.
3. Material and methods
The specimen, LPM (Liaoning Paleontological
Museum)-R00076, is an incomplete and scattered
skeleton, including a partial skull and lower jaws,
six cervical vertebrae, at least nine dorsal vertebrae,
partial pectoral girdles, humeri, ulnae, radii, wing
metacarpals, wing phalanges 1-4; femora and tibio -
tarsi. It was collected in 2005 from a locality
(41°34’20”N, 120°09’30“E), which is near Yuan -
jiawa Village, Dapingfang, Chaoyang, western Liao-
ning. The specimen was prepared carefully by using
mechanical tools in LPM, and is deposited in LPM,
Shenyang Normal University.
4. Description
The specimen (LPM-R00076) is a medium-sized
pterosaur with an estimated wingspan of 1.45 m, less
than the holotype, in which the wingspan is estimated
as 1.71 m. It most probably represents a juvenile
individual and displays several immature features,
such as an unfused extensor tendon process of the first
wing phalanx, and separated scapula and coracoid
(e.g. B
ENNETT
1993).
Sku ll. The anterior part of the skull is the most
extensive part preserved. The snout is low, long, and
pointed, with a large nasoantorbital fenestra, but the
complete boundaries of the fenestra are uncertain
because of poor preservation. In addition, a part of the
braincase isolated from the skull exposes its roof
in ventral view. Two large and smooth depressions
separated by a low sagittal ridge possibly represent the
cerebral region, as in Rhamphorhynchus, Anhanguera,
and Pteranodon (B
ENNETT
2001; W
ITMER
et al. 2003);
each depression is semicircular as in Anhanguera and
Pteranodon. The sagittal ridge is deeper anteriorly
than posteriorly and distally is confluent with a bony
wall. Posterolaterally, an elliptical depression meets
the sagittal ridge at an acute angle. This depression is
smaller and slightly higher than the cerebral region,
and may mark the position of the optic lobe. The
shape of the optic lobe is swollen, more like that in
Rhamphorhynchus than in Anhanguera and Pterano -
don. Another smaller, circular depression just behind
Chaoyangopterus from the Early Cretaceous Jiufotang Formation of western Liaoning, China 343
Fig. 2. The stratigraphic section of the fossil site and adja-
cent area, identified as the Yuanjiawa beds of the Jiufotang
Formation. The pterosaur fossil (LPM-R00076) is from the
shale layer that is marked by asterisk, and associated fossils
include fish and bird fossils. I-III, representing three brown-
yellow marl layers. Modified from D
UAN
et al. (2005).
Scale equals 50 cm.
344 Chang-Fu Zhou
the cerebral region represents an unknown part of the
brain.
The lower jaws overlap each other, and are missing
their proximal ends. The preserved length of the lower
jaws is about 190 mm, of which the symphysis is
about 105 mm, but there is no evidence of a ventral
sagittal crest at the distal end of the symphysis, and
thus differing from Eopteranodon (L
Ü
& Z
HANG
Fig. 3. Chaoyangopterus zhangi W
ANG
& Z
HOU
, 2003, an incomplete and scattered skeleton, LPM-R00076, collected from
a site (41°34’20”N, 120°09’30”E) near Yuanjiawa Village, Dapingfang, Chaoyang, western Liaoning, China. Its precise
horizon is Yuanjiawa beds of Jiufotang Formation (middle Early Cretaceous, Aptian) with a radiometrical dating of 120 Ma.
Abbreviation: br, braincase; c, coracoid; cve, cervical vertebrae; dve, dorsal vertebrae; lf, left femur; lh, left humerus;
lr, left radius; lu, left ulna; lw, lower jaws; mc I-III, metacarpal I-III; mds, manual digits; rf, right femur; rh, right humerus;
ribs, ribs; rr, radius; ru, right ulna; s, scapula; sa, sacrum; sk, skull; t, tibiotarsus; u, ulna; wmc, wing metacarpal; wp1-4,
wing phalanges 1-4; ?, unknown bones. Scale equals 50 mm.
2005). The elongate symphysis is similar to that in
Chaoyangopterus and Jidapterus (W
ANG
& Z
HOU
2003; D
ONG
et al. 2003).
Axial skeleton. – The caudal-most four cervical
and as many as six dorsal vertebrae are articulated in a
series. A second series comprises three or four dorsal
vertebrae and the sacrum. In addition, two isolated
vertebrae appear to be anterior cervicals. The smaller
of these two may be the axis in posterior or anterior
view. The centrum appears to be broken away from the
neural arch. A small neural canal that is 4 mm wide
and 2 mm high is enclosed by the neural arch. Above
the canal, however, the detailed morphology of the
neural arch is obscure. In contrast, the second cervical
vertebra is elongate and exposed in ventral view with
a length of 26 mm. Much of its morphology is
obscured by damage to its lateral wall. There is a
shallow and longitudinal groove at the base of the
prezygapophysis. A possible rib is preserved against
the second cervical vertebra; but other cervicals lack
evidence of ribs.
Chaoyangopterus from the Early Cretaceous Jiufotang Formation of western Liaoning, China 345
Fig. 4. The mid-cervical vertebrae of Chaoyangopterus zhangi W
ANG
& Z
HOU
, 2003 (LPM-R00076). Abbreviations:
dve, dorsal vertebrae; ls, longitudinal sulcus; ns, neural spine; pc, posterior condyle; pex, postexapophysis; poz, post -
zygapophysis; prz, prezygapophysis; przt, prezygapophysis tubercle. Scale equals 20 mm.
346 Chang-Fu Zhou
The posteriormost four cervicals (Fig. 4) that are
articulated with the dorsals are distinctly longer
than the second cervical, having lengths of 40 mm,
40.4 mm, 37.9 mm, and 37.5 mm respectively. The
neural arch is fused to the centrum. No pneumatic
foramina penetrated the lateral side of the cervicals,
resembling Jidapterus, Eopteranodon and Eoazh -
darcho in this respect. In the cervical series, the first
vertebra is exposed laterally and ventrally and is
strongly procoelous. The preserved posterior part
of the neural spine is low and blade-like. The right
prezygapophysis is exposed laterally, with a shallow
and long groove at its base, resembling the longi -
tudinal sulcus of the long-necked azhdarchids, such
as Azhdarcho, Phosphatodraco, Arambourgiania,
Quetzalcoatlus, and an unnamed Hungarian azhdar-
chid (e.g. M
ARTILL
et al. 1998; ˝
O
SI
et al. 2005;
H
ENDERSON
& P
ETERSON
2006). The medial side of
the prezygapophysis is exposed with an oval articular
surface that faces more medially than dorsally, having
a flat ventromedial tubercle, the prezygapophysis
tubercle, as in the long-necked azhdarchids (˝
O
SI
et al.
2005). The postzygapophysis is stout and extends
posterolaterally. In contrast, the posterior articular
condyle and the postexapophyses, which form the
posterior end of the cervical centrum, extend poster -
iorly far beyond the postzygapophysis. The left
postexapophysis is obscured by the prezygapophysis
of the next successive vertebra. The second cervical
is almost complete except for damage to the neural
spine, seen in lateral view. The well-developed pre -
zygapophysis is ventral to the level of the postzygapo-
physis, as an artifact of compaction. The postzygapo-
physis is comparable to the distal end of the centrum
in size. Distally, the postexapophysis extends slightly
beyond the articular condyle. The penultimate cervical
is exposed in ventral view. The centrum gradually
increases in width from its mid-part to the anterior and
posterior ends, respectively. The prezygapophyses are
well developed and nearly parallel to each other, as in
the long-necked azhdarchid pterosaurs. However, the
cervical has a low ratio (2.1) of length (from the tip of
the prezygapophysis to the end of the postexapopysis)
to width (across the prezygapophyses), differing from
the extremely elongate cervicals of azhdarchids.
The centrum is smooth without a ventral keel. The
postexapophyses are well developed with a width
of 13 mm and forming prominent corners on the
centrum. The last cervical vertebra is exposed ven -
trally and slightly laterally; it is slightly shorter
than the penultimate cervical. In addition, the distal
extension of the postexapophyses is strongly reduced
to the level of the postzygapophyses.
Compared with the cervicals, the dorsal vertebrae
are poorly preserved. There are two series of dorsals:
the anterior series is articulated with the cervicals;
the posterior part is adjacent to the sacrum. The first
of the dorsal series is cervicalized, representing a
transition from the neck to the dorsal column, with
a length of 11 mm. It well articulates with the last
cervical vertebra. Other dorsals of the anterior series
are damaged and yield no useful information, thereby
it is uncertain whether the notarium is present or not in
LPM-R00076. The posterior part of the dorsal series is
preserved with the centra exposed in lateral view. The
dorsal centra are smooth ventrally without a keel.
Their mean length is about 7 mm. The sacrum is
damaged, lacking any useful information.
Rib s. A possible cervical rib is present near the
isolated cervical vertebra. Anterior dorsal ribs are
short and robust, and are in articulation with the dorsal
vertebrae, but they are poorly preserved. Other ribs
are scattered around the skull.
Pectoral girdle. – The pectoral girdle is composed
of the scapula and coracoid; these are separated in
LPM-R00076, rather than fused as in adult pterosaurs.
The scapula is relatively stronger and slightly longer
than the coracoid. The right scapula is well exposed
and weakly curved. Its blade is mostly straight and
unconstricted, but curves medially and ventrally in its
proximal third. Because the right coracoid is obscured
by the right scapula, its morphology cannot be de -
termined except at its distal end. In contrast, the left
coracoid is well-exposed, and has a broad proximal
end with a distinct flange. The shaft is clearly con -
stricted at its midpoint, and then slightly broadens
near its distal end. The distal end of the coracoid
exhibits two small condyles separated by a shallow
groove, forming a concave facet for articulation with
the sternal plate.
Forelimb. – The forelimb bones are scattered, so
the original position of its elements are difficult to
determine. Both humeri are well preserved. The left
humerus is exposed in dorsal view, and the right
one in ventral view. The pneumatic foramen is not
preserved on the proximal end of the humerus. The
humeral head is saddle-shaped, as in other pterosaurs.
A well-developed deltopectoral crest is situated at the
proximal end of the humerus. Its medial margin is at
the same level as the humeral head. The deltopectoral
crest extends down about 21% of the humeral shaft,
and quite distinct from the high ratio (40 %) seen in
pteranodontids, and is not warped as in the Pterano -
dontidae (B
ENNETT
1989). Associated with the delto-
pectoral crest, a prominent posterior tuberosity is
developed on the opposite side. However, the tubero -
sity is obscured by the overlapping tibiotarsus. Distal
to the deltopectoral crest, the humeral shaft is straight
and strongly constricted, and then the shaft is slightly
expanded distally in its distal half. The condyles at the
distal end of the humerus are not well ossified, further
implying that LPM-R00076 is an immature indi -
vidual.
The ulna and radius are comparable to each other in
size, as in Jidapterus (D
ONG
et al. 2003), but different
from Eoazhdarcho, in which the ulna is much wider
than the radius (L
Ü
& J
I
2005), and they are distinctly
elongate (40 % longer than the humerus).
The wing metacarpal is well developed, with a
length of 148 mm, and is notable for its broad
proximal end and oval, bicondylar joint distally.
Proximally, the wing metacarpal is expanded antero-
posteriorly. However, the shaft is gradually constricted
anteroposteriorly and expanded dorsoventrally to form
the distal bicondylar joint. The two well-defined
condyles are separated by a deep intercondylar groove
for articulating with the first wing phalanx. Meta -
carpals I-III are scattered around the wing metacarpal.
They are very slender and much shorter than the wing
metacarpal. Compared with their slender shafts, the
distal ends of the metacarpals I-III are distinctly
expanded for articulation with digits I-III.
The wing phalanges of digit IV are also disarti -
culated. There are four of these phalanges that are
preserved together, with the distal three in a row; these
decrease in length and are the phalanges of the wing
finger. The first three phalanges have a constricted
shaft between the expanded ends. The first wing
phalanx is the longest limb element of LPM-R00076.
Associated with the wing metacarpal, the first wing
phalanx has a convex proximal articular surface.
However, the extensor tendon process is not fused to
the proximal end of the first wing phalanx, which is
an important immature feature in pterosaurs (e.g.
B
ENNETT
1993). The pneumatic foramen is not pre -
served on the proximal end of the first wing phalanx
in LPM-R00076. The distal end of the first wing
phalanx is expanded to form a foot-like process. In
contrast, the distal wing phalanges are distinctly
reduced in size (Table 1). The fourth wing phalanx as
preserved has a length of 54 mm, but its distal end is
damaged. Other digits are poorly preserved and yield
no useful information.
Hindlimb. – The right femur is exposed in posterior
view, and the left in anterior view. The femoral head is
mediodorsally oriented, resulting in a total length of
the femur of 107.7 mm. Below the head, a distinct
neck joins the femoral shaft. The shaft of the right
femur is straight, while that of the left is slightly
curved medially. The shaft gradually becomes slightly
broader distally, and is best seen in the left femur. The
distal end of the right femur has two condyles; these
are comparable to each other in size, except that the
external condyle is expanded more posteriorly than
the internal one. The distal end of the left femur is
obscured by the overlapping lower jaws.
As in other edentulous pterosaurs, the tibiotarsus
is slightly shorter than the first wing phalanx in
LPM-R00076, with a length of 156 mm. The shaft of
the tibiotarsus is straight; its proximal end is expanded
and its distal end constricted. The pes is not preserved
in this specimen.
4. Discussion
In the Jehol Biota, there are six possible azhdarchoids
Chaoyangopterus zhangi, Jidapterus edentus, Eopte -
ranodon lii, Eoazhdarcho liaoxiensis, Nemicolopterus
crypticus, and Shenzhoupterus chaoyangensis, with a
low and strongly elongate snout and lower jaws
(W
ANG
& Z
HOU
2003; D
ONG
et al. 2003; L
Ü
& Z
HANG
2005; L
Ü
& J
I
2005; L
Ü
et al. 2008; W
ANG
et al.
2008b). Based on the above description, LPM-
R00076 is comparable to these taxa in cranial
morphology. However, LPM-R00076 differs from
Eopteranodon in lacking the dentary crest and the
wing metacarpal that is equal in length to the second
wing phalanx. LPM-R00076 differs from Eoazhdar-
Chaoyangopterus from the Early Cretaceous Jiufotang Formation of western Liaoning, China 347
Table 1. Measurements of Chaoyangopterus zhangi W
ANG
& Z
HOU
, 2003 (LPM-R00076).
Right (length mm) Left (length mm)
Scapula/Coracoid 56.3/45.2 ?/44.8
Humerus 78 79
Ulna/Radius 110.5/111.3 >108/>110
Wing metacarpal 149.4 151
Wing phalanges 1-4 164/112/71/>34 162/112/70/?
Femur 107.7 106
Tibiotarsus 158 156
348 Chang-Fu Zhou
cho by lacking the humerus and femur that are equal
in length, and the deltopectoral crest that is 33 % of
the length of the humerus. The difference of LPM-
R00076 from the recently erected Shenzhoupterus is
lacking the convex lower jaw margin, and relatively
short tibiotarsus. In contrast, LPM-R00076 is com -
parable to Chaoyangopterus zhangi and Jidapterus
edentus in the proportions of the limbs. However,
LPM-R00076 lacks a pneumatic foramen on the
proximal end of first wing phalanx that has been
reported in Jidapterus edentus (L
Ü
et al. 2006a).
Therefore, LPM-R00076 is identified as Chaoyango -
pterus zhangi on the basis of the similar skull shape
and limb proportions.
Recently, W
ANG
& Z
HOU
(2006) argued that Jida -
pterus, Eopteranodon, and Eoazhdarcho are syno-
nyms of Chaoyangopterus in the Pteranodontidae, but
without providing an explicit justification. However,
the opposite opinion that these taxa are valid, and most
or all of them pertain to the Azhdarchoidea, is pre -
ferred by L
Ü
& J
I
(2006), L
Ü
et al. (2006a), A
NDRES
& J
I
(2008), and L
Ü
et al. (2008). A phylogenetic
analysis by L
Ü
& J
I
(2006) suggested that these
Chinese taxa may pertain to the Azhdarchoidea,
and that Chaoyangopterus and Jidapterus are more
derived than Eopteranodon and Eoazhdarcho within
this clade. However, L
Ü
et al. (2006a: 66-71) initially
identified these taxa as pteranodontids (Chaoyango -
pterus, Jidapterus, and Eopteranodon) and azhdar-
choids (Eoazhdarcho), but later indicated that they are
all possible azhdarchoids (see L
Ü
et al. 2006a: 97), or
possible pteranodontid (Eopteranodon) and azhdar-
choids (Chaoyangopterus, Jidapterus, and Eoazh -
darcho) (see L
Ü
et al. 2006a: 115). Recently, a phylo-
genetic analysis by A
NDRES
& J
I
(2008) showed that
Chaoyangopterus, Jidapterus, and Eoazhdarcho unite
together as the sister group of Azhdarchidae, while
Eopteranodon falls within the Tapejaridae. Lastly, a
clade, Chaoyangopteridae, erected by L
Ü
et al. (2008)
to include the five taxa, was assigned to the Azhdar-
choidea. In fact, these arguments are mainly due to the
limited anatomical information about these taxa in
their original descriptions. Therefore, a more reliable
phylogeny can only be performed by reexamining
specimens of these taxa, but this is not the purpose of
this study. In this context, based on the new material
(LPM-R00076), the taxonomic position of Chaoyang-
opterus itself is discussed.
Within the Pterodactyloidea, there are three eden-
tulous clades: Nyctosauridae, Pteranodontidae, and
Azhdarchoidea (Tapejaridae and Azhdarchidae) (e.g.
K
ELLNER
2003). LPM-R00076 differs from the
Nyctosauridae in lacking a hatched-shaped delto -
pectoral crest and an extremely elongate wing meta-
carpal IV (250 % the length of the humerus); and from
the Pteranodontidae in lacking tall and spike-like
neural spines on the mid-cervical vertebrae, a scapula
shorter than the coracoid; and a warped deltopectoral
crest on the humerus. Chaoyangopterus possibly
belongs to the Azhdarchoidea by sharing one synap-
morphy, the ratio of the length of the second wing
phalanx to that of the first is less than 0.70 (K
ELLNER
2003). Within the Azhdarchoidea, however, Chao -
yangopterus can be confidently excluded from the
Tapejaridae by the low and strongly elongate snout
and lower jaws, and can be distinguished from the
Azhdarchidae by its moderately elongate mid-cervical
vertebrae. Except for the moderately elongate mid-
cervicals, however, Chaoyangopterus (LPM-R00076)
shares a character with the Azhdarchidae: the lateral
pneumatic foramina are absent on the cervical verte-
brae. Additional characters of the cervical vertebrae
are similar to the extremely elongate mid-cervicals of
the Azhdarchidae, such as the horn-like and slightly
divergent prezygapophyses (H
OWSE
1986), and a
longitudinal sulcus at the base of the prezygapophysis
(˝
O
SI
et al. 2005). Therefore, Chaoyangopterus appears
to have a close relationship with the Azhdarchidae,
consistent with the phylogenetic results of L
Ü
& J
I
(2006), L
Ü
et al. (2006a), A
NDRES
& J
I
(2008), and
L
Ü
et al. (2008); but the moderately elongate mid-
cervicals and the blade-like neural spines imply that
Chaoyangopterus possibly represents a distinct clade
(the family Chaoyangopteridae) from the Azhdarchi-
dae, as suggested by A
NDRES
& J
I
(2008) and L
Ü
et al.
(2008).
The Azhdarchidae characteristically possess ex -
tremely elongate mid-cervical vertebrae with strongly
reduced or absent neural spines, and flourished to the
end of the Cretaceous (e.g. L
AWSON
1975; W
ELLN
-
HOFER
1991; H
ENDERSON
& P
ETERSON
2006). How -
ever, a similar condition of the mid-cervical vertebrae
has been reported in the tooth-bearing Ctenochas -
matidae, implying a homoplasy of the extremely
elongate mid-cervical vertebrae between the two
clades (e.g. A
NDRES
& J
I
2008). Associated with the
elongate mid-cervical vertebrae, the strongly reduced
or absent neural spines and well-developed postexapo-
physes are present in both groups. In contrast, the
mid-cervical vertebrae of the azhdarchids are distinct
from those of the ctenochasmatids in lacking lateral
pneumatic foramina. However, the evolution of the
Azhdarchidae is still poorly understood, especially in
the extremely elongate mid-cervical vertebrae.
Recently, a hypothesis further enhanced the argument
on the evolution of the azhdarchids by A
NDRES
& J
I
(2008) that low and blade-like neural spines were
absent in the lineage from which the azhdarchids were
descended.
As the recent phylogenetic results, the Chao -
yangopteridae is a sister group of the Azhdarchidae
(A
NDRES
& J
I
2008; L
Ü
et al. 2008). The moderately
elongate mid-cervicals with low and blade-like neural
spines are present in Chaoyangopterus, well opposing
to the hypothesis of A
NDRES
& J
I
(2008). A similar
condition was reported in the holotype of Eoptera -
nodon (L
Ü
& Z
HANG
2005), but not in its referred
specimen (L
Ü
et al. 2006c). The moderately elongate
mid-cervicals with low and blade-like neural spines
have not been reported in other Chaoyangopterus-like
taxa, perhaps because of the poor preservation of
the mid-cervical vertebrae, or a primitive position
of Chaoyangopterus relative to other taxa in the
Chaoyangopteridae, but this need be further con -
firmed by additional material. In fact, several azhdar-
chid taxa have been reported with a tall and blade-like
neural spine on the first or last mid-cervical vertebra,
such as Quetzalcoatlus, Zhejiangopterus and Phos-
phatodraco (P
EREDA
S
UBERBIOLA
et al. 2003; A
NDRES
& J
I
2008). Therefore, these discoveries may suggest
that the Azhdarchidae are possibly derived from a
Chaoyangopterus-like lineage that has moderately
elongate mid-cervical vertebrae with low and blade-
like neural spines.
Acknowledgements
This study was supported by grants from the National
Scientific Foundation of China (Grant #40802007) and
from the Ph.D. Start-up Foundation of Shenyang Normal
University. The author would like to thank the director of
Institute of Paleontology, S
HAO
-L
I
C
HENG
for accessing the
fossil, and S
HU
-R
UI
Y
ANG
and Q
IANG
Y
ANG
for their skillful
preparation. I would like to express my gratitude to Prof.
R
ICHARD
C. F
OX
(University of Alberta, Canada) and Prof.
K
E
-Q
IN
G
AO
(Peking University, China) for encouraging me
to study this field and for their stimulating discussions and
helpful corrections about the earlier versions of the
manuscript. I would like to thank Dr. S. C
HRISTOPHER
B
ENNETT
(Fort Hays State University, Kansas, U.S.A) and
Dr. D
AVE
M
ARTILL
(University of Portsmouth, Portsmouth,
UK) for their critical reviews of the manuscript that their
suggestions have greatly improved the quality of the
manuscript.
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Manuscript received: May 18th, 2009.
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2009.
Address of the author:
C
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Z
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Shenyang Normal University, 253 North Huanghe Street,
Shenyang, Liaoning 110034, China;
e-mail: zhoucf528@163.com
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