1112 Chinese Science Bulletin Vol. 46 No. 13 July 2001
Discovery of a pterodactylid
pterosaur from the Yixian
Formation of western
WANG Xiaolin1,2 & LÜ Junchang1,3
1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese
Academy of Sciences, Beijing 100044, China;
2. College of Earth Sciences and Resources, China University of Geo-
sciences, Beijing 100083, China;
3. Department of Geological Sciences, Southern Methodist University,
Dallas, TX 75275, USA
-897,.9 A well-preserved pterosaur with nearly com-
plete skull is described from the Lower Cretaceous Yixian
Formation at Sihetun in western Liaoning. It is character-
ized by a low and long crestless skull, slender and pointed
teeth, long metacarpal, nearly equal length of metatarsals
and short pedal digit . It is referred to a new genus
and species of the family Pterodactylidae: Haopterus gracilis
gen. et sp. nov. This is the first pterosaur with a nearly com-
plete skull from the Jehol Biota; it also represents the first
non-controversial fossil record of Pterodactylidae in Asia.
Haopterus is more derived than Pterodactylus from the Late
Jurassic Solnhofen in Germany. This discovery extends the
distribution of the family Pterodactylidae from Europe and
Africa to Asia and its latest occurrence from the Late Juras-
sic to the Early Cretaceous. The discovery of Haopterus
gracilis provides further evidence for the study of the origin
and radiation of the Jehol Biota; it also sheds new light on
the evolution and distribution of pterosaurs in the late
Keywords: western Liaoning, Early Cretaceous, Yixian Formation,
Western Liaoning Province is most notable for the
excellent preservation of the famous Jehol Biota. Recently,
a lot of important vertebrate fossils[1,2] including the
primitive bird Confuciusornis and various feathered di-
nosaurs have been discovered from the lacustrine de-
posits of the third member of the Early Cretaceous low
Yixian Formation at Sihetun, Beipiao, Chaoyang[1,2].
These fossils form a unique vertebrae assemblage from
the terrestrial lake deposits in the Mesozoic and represent
an important biological radiation event in the Early Cre-
taceous; it provides important evidence for the study of
the origin and early radiation of major vertebrate groups
such as birds.
A total of more than 10 individual pterosaurs have
recently been discovered from the lower Yixian Formation
in Sihetun areas, western Liaoning Province. Most of
them were referred to Eosipterus and Dendrorhyn-
choides, respectively; others remain unnamed. None of
these specimens preserved the skull, therefore their phy-
logenetic position remain controversial[7,8]. A new speci-
men of pterosaur was collected during the field season of
the IVPP (Institute of Vertebrate Paleontology and Pa-
leoanthropology) in 1998, it contains a nearly complete
skull and most of the postcranial bones. It is the first in-
disputable remains of the family Pterodactylidae from
Asia, and extends the distribution from Europe and Africa
to Asia and its latest occurrence from the Late Jurassic to
the Early Cretaceous. The discovery of Haopterus gracilis
gen. et sp. nov. provides further evidence for the study of
the evolution and distribution of pterosaurs in the late
1 Systematic paleontology
Order Pterosauria Kaup, 1834
Suborder Pterodactyloidea Plieninger, 1901
Family Pterodactylidae Bonaparte, 1838
Genus Haopterus gen. nov.
Species Haopterus gracilis gen. et sp. nov.
Diagnosis. Small to medium-sized pterosaur. Maxi-
mum wingspan 1.35 m. Skull length 145 mm. Skull low
and long; rostrum pointed; crest absent at the rear of the
skull; nasopreorbital opening elongate and elliptical. 12
pointed and posteriorly inclined teeth in both upper and
lower jaws. Teeth of the premaxilla (first 3 teeth of the
upper jaw) slender. Fourth and more posterior teeth con-
stricted at the base. Teeth extend posteriorly toward the
middle of the nasopreorbital opening, about 66.4% of the
lower jaw equipped with teeth. Forelimb robust. Humerus
short, robust and straight, delto-pectoral crest expanded
and semicircular. Wing metacarpal long and about 1.3
times that of the humerus. Phalanges of the wing
digit longer than wing metacarpal. Ulna and phalanx I of
wing digit 1.1 and 1.4 times that of the wing metacarpal,
respectively. Metatarsals reduced; Metatarsals of
nearly equal length; metatarsals and reduced and
short; Length of metatarsal about 18.7% that of wing
metacarpal. Sternum fan-shaped; its length equals its
width; keel well-developed.
Holotype. A nearly complete skeleton that con-
tains a complete skull and pectoral girdle, forelimbs, ster-
num, cervical, dorsal, metatarsals and digits. Institute of
Vertebrate Paleontology and Paleoanthropology specimen
number: IVPP V11726 (figs. 1 and 2).
Etymology. The genus name is dedicated to Prof.
Yichun Hao, a distinguished Chinese paleontologist who
has contributed significantly to the study of the Jehol Bi-
ota; the species name reflects both the beautiful preserva-
tion and the tiny metatarsals of the holotype.
Horizon and locality. Locality 1 at Sihetun, Shan-
gyuan, Beipiao, western Liaoning; Jianshangou Bed of the
lower Yixian Formation[1,2], late Valanginian (age of
Jurassic/Cretaceous boundary is 135 Ma) or Barremian
Chinese Science Bulletin Vol. 46 No. 13 July 2001 1113
Fig. 1. Haopterus gracilis gen. et sp. nov. (IVPP V11726, holotype).
(Jurassic/Cretaceous boundary is 144 Ma) of the Early
Description. A nearly complete subadult individ-
ual with skull but lacks pelvis, femur, tibia, fibula, caudal
and sacral. Both ends of long bones are less well ossified.
Measurements of major skeletal elements are listed in
Skull. The skull is lateroventrally preserved. It is
low and 145 mm long. The rostrum is pointed. The crest is
absent at the rear of the skull. There are 12 teeth in both
the upper and lower jaws. The 5 front teeth are slender,
more posterior teeth are constricted at the base. Teeth
number is less than that of pterodactylus.
The premaxilla and the maxilla are fused; no suture
is recognizable between these two bones. Teeth extend
from the anterior end to the middle of the nasopreorbital
opening. Teeth are pointed and posteriorly inclined. Teeth
of the premaxilla (first 3 teeth of the upper jaw) represent
tiny replaceable teeth. The nasopreorbital opening is
elongate and elliptical and 40mm long, which is 27.6%
that of the skull length. The nasal is small and nearly ver-
tical near the dorso-posterior margin of the nasopreorbital
opening. The nasal overlaps the adlacrimal. The frontal is
missing. Most of the bones of the posterior skull are
crushed and undistinguishable, but the left squamosal and
jugal are recognizable.
Table 1 Measurements of skeletal elements of the holotype
(IVPP V11726) of Haopterus gracilis gen. et sp. nov.
Name Left/mm Right/mm
Humerus 70 60+
Ulna 101 102
Wing metacarpal 89 91
First phalanx of wing digit 141 138
Second phalanx of wing digit 119 119
Third phalanx of wing digit 95 96
Fourth phalanx of wing digit 44+ 45+
Pteroid − 34
Metatarsal 17 17
Metatarsal 17 17
Metatarsal 17 17
Metatarsal 13 13
Metatarsal 5 −
Sternum 45 (length) 46 (width)
Lower jaw 128 85 (with dentition)
The posterior part of the lower jaw is toothless. The
lower jaw with dentation is 85 mm long, which is 66.4%
of the total length of the lower jaw. The teeth of the lower
jaw are similar to those of the upper jaw in size, shape and
1114 Chinese Science Bulletin Vol. 46 No. 13 July 2001
Fig. 2. The outline of the skeleton of Haopterus gracilis gen. et sp. nov. (IVPP V 11726, holotype). a, Angular; al, adlacrimal; c, carpal;
ce, cervical vertebrae; cor, coracoid; cris, cristospine; d, dentary; do, dorsal vertebrae; dp, delto-pectoral crest; ga, gastralia; hu, humerus;
is, ischium; j, jugal; m, maxilla; mc , metacarpals ; mt , metatarsals ; n, nasal; npo, nasopreorbital open-
ing, pm, premaxilla; po, postorbital; pt, pteroid; q, quadrate; r, radius; ri, rib; sa, surangular; sc, scapula; sq, squamosal; ster, sternum; t,
tarsal; u, ulna; wph , wing phalanges ; , fingers .
pattern; the first tooth is slightly inclined anterolaterally.
The angular and the surangular are tightly attached to the
dentary. The quadrate is long, plate-shaped and slightly
curved dorsally. The hyoid is slender and 52 mm long.
Cervical and dorsal vertebrae
are preserved, but sacrals and caudals are missing. Cervi-
cal vertebrae are crushed together with the posterior skull
bones. The anterior 8 dorsal vertebrae are preserved, their
combined length is 52 mm. The dorsal vertebra is pro-
coelous. The anterior dorsals are short and become pro-
gressively elongate distally. Some incomplete ribs and
isolated gastralia are preserved.
Pectoral girdle and forelimb. The left pectoral
girdle is ventrally preserved while the right side is dor-
sally preserved. The left coracoid is completely preserved;
it is rod-like, straight and thick-walled; the proximal end
is robust with a procoracoid process in articulation with
the scapula; distally it is not expanded, and has an obvious
articulation with the sternum; ventrally it has a longitudi-
nal groove which becomes wider distally. The left scapula
is complete; it is thin, plate-shaped; its length is about
88.2% that of the scapula; distally the scapula is expanded
Chinese Science Bulletin Vol. 46 No. 13 July 2001 1115
Both the left and right humeri lack the proximal end.
The humerus is straight; the delto-pectoral crest is semi-
circular and expanded laterally; the left humerus is in ar-
ticulation with the coracoid and scapula.
The right radius, ulna and the left ulna are well pre-
served and in articulation with the humerus and the car-
pals. The radius and the ulna are straight, thin-walled and
expanded at both ends. The radius is slender and slightly
longer than the ulna.
The carpals are small; left carpals are crushed to-
gether with the posterior skull bones and cervical verte-
brae. The left pteroid is well preserved; it is slender and
straight but does not taper toward the distal end.
The metacarpals are not completely preserved.
Metacarpals are nearly of equal length, they are
slightly longer than the humerus but are shorter than the
ulna. Metacarpals are slender; they are parallel
and tightly attached to metacarpal . Metacarpal
(wing metacarpal) is robust; it is proximally expanded and
in close contact with the carpals; distally it is in articula-
tion with the wing digit. The wing metacarpal is 1.3 times
the length of the humerus. The ulna is 1.1 times as long as
the wing metacarpal.
The digits are completely preserved. Digits
are completely preserved on the right side and digits
are preserved on the left side. Digits are
slender, the distal phalanges are short and the unguals are
sharp. Digit IV is long and preserved all 4 phalanges; they
are all robust, straight and thin-walled; they are expanded
at both ends, with the proximal end wider than the distal
end. The fourth phalanx of the wing digit tapers distally
although its distal extremity is missing. The length of the
phalanges of the wing digit decreases toward to the distal
end; the first three phalanges are longer than wing meta-
carpal; the first phalanx is 1.4 times as long as the wing
metacarpal. The phalangeal format of the hand is 2-3-4-4.
To compare the length of the major elements of the
forelimb, we list them in progressively decreasing order as
follows: first phalanx of the wing digit, second phalanx of
the wing digit, ulna, third phalanx of the wing digit, wing
metacarpal, humerus, fourth phalanx of the wing digit.
The sternum is fan-shaped. The keel is well devel-
oped and extends anteriorly to one third of the sternal
plate; it is about half as long as the sternum. The sternum
is thin; its length equals the width. Ventrally it is most
similar to that of Gallodactylus and Nesodactylus.
Pelvic girdle and hindlimb. Only the posterior
margin of the left ischium is preserved, it is semicircular
and thin, with the dorsal margin thickened. It is most
similar to the ischium of Pterodactylus.
Most of the hindlimb elements are missing. Tarsals,
metatarsals and a few pedal digits are preserved. Proximal
tarsals are large and the distal tarsals are small and fused.
Compared to the forelimbs, the metatarsals and digits are
extremely reduced and small. Metatarsals are of
equal length; is slightly shorter; is shorter than
. The length of metatarsal is only about 18.7% that
of the wing metacarpal. Digits and also preserved
the unguals. Digit has only one short phalanx and
preserved its impression. The pedal phalangeal format is
2 Comparisons and discussions
Among the two suborders of Pterosauria the Rham-
phorhynchoidea occurred from the Late Triassic to the
Late Jurassic and is characterized by the presence of a
long tail while the short-tailed Pterodactyloidea has been
known from the Late Jurassic to the Late Cretaceous.
Haopterus gracilis gen. et sp. nov. is characterized by a
low and long crestless skull, a unified nasopreorbital
opening, short teeth in both the upper and lower jaws,
short pedal digit and long wing metacarpal. These
characters show that Haopterus should be referred to the
Pterodactyloidea. Based on the character of the nearly
complete skull including the dentition, it can be compared
with the known members of different families of Ptero-
Pterodactyloidea comprises 15 families, among
them are the Late Cretaceous toothless Pteranodontidae,
Nyctosauridae, Azhdarchidae from North America and the
Tapejaridae from the Early Cretaceous of Brazil and An-
hangueridae, Criorhynchidae, Germanodactylidae and
Dsungeripteridae that possess both teeth in the jaws and a
crest on the skull[10 12]. Among the families that possess
teeth but lack a skull crest are Ctenochasmatidae from the
Late Jurassic of Germany, France and the Early Creta-
ceous of China and Pterodaustridae form the Early
Cretaceous of Argentina and Chile; these groups possess
several hundred dense teeth in both the upper and lower
jaws. Some members of the family Ctenochasmatidae also
have a skull crest[9,10], which can be easily distinguished
from Haopterus. Cearadactylidae from the Early Creta-
ceous Santana Formation in Brazil comprises large-sized
pterosaurs that have a small skull with especially long and
robust teeth. Ornithodesmidae from the Early Creta-
ceous (Wealden) of England has short and robust teeth
and a duck-bill-shaped rostrum. Both of these families
are distinguishable from Haopterus. Besides, the family
Ornithocheridae, which is widely distributed in the Early
Cretaceous to the Late Cretaceous deposits in Europe,
Africa, South America and Australia, comprise large-sized
pterosaurs which have a low and slender skull, and the
teeth are short, pointed and densely distributed. A few
members of this family also possess a skull crest.
Haopterus is a small to medium sized pterosaur. Its
skull characters are most similar to those of the Late Ju-
rassic Pterodactylidae and Gallodactylidae from
1116 Chinese Science Bulletin Vol. 46 No. 13 July 2001
Europe[9,10]; the later two families are distinguishable from
each other by both the teeth morphology and the postcra-
nial characters. Gallodactylidae has slender teeth, which
are only distributed in the anterior jaws and a short crest at
the rear of the skull. The dentition of Haopterus as well as
other characters is most similar to that of Pterodactylidae,
therefore Haopterus is referred to the family Pterodac-
Pterodactylidae is composed of one genus (Ptero-
dactylus) and 13 species. Haopterus can be clearly dis-
tinguished from Pterodactylus by the following character:
fewer teeth, fusion between the premaxilla and the maxilla,
fusion of the tarsals, sternum with a well-developed carina,
well-developed pectoral girdle, more expanded delto-
pectoral crest of the humerus, well-developed procoracoid,
more developed wing digit, the first three phalanges of the
wing digit longer than the wing metacarpal. All these
characteristics are related to more powerful flying capa-
bility. In addition, Haopterus also has very reduced meta-
tarsals, Metatarsals are of equal length and less
than one fifth of the length of the wing metacarpal while
Pterodactylus has more developed hindlimbs. Compared
with Pterodactylus, Haopterus is probably more adapted
to flight than terrestrial life.
Pterosaurs were believed to be more adapted to bi-
pedal locomotion based on its forelimb and pectoral girdle
structure; however, further work on large pterosaur
Anhanguera from the Early Cretaceous Santana Forma-
tion of Brazil indicates that they probably lived a quadru-
pedal life. The extremely reduced hindlimb of Haop-
terus indicates that it cannot be bipedal; small to medium-
sized pterosaurs were probably quadrupedal most of the
Haopterus has a large skull and a pointed rostrum;
the front teeth are sharp and slender, suggesting a pis-
civorous feeding habit. It probably has strong flight capa-
bility and the body was suspended by the hindlimb in
Eosipterus from the same horizon as Haopterus did
not preserve the skull; the limb bones were not completely
preserved. It can be easily distinguished from the latter by
the following characters: the ulna is as long as the first
phalanx of the wing digit, but is 1.3 times as long as the
wing metacarpal, metatarsals are relatively long, metatar-
sal I is about 57.5% of the length of the wing metacarpal.
Eosipterus was recently referred to the Pterodactyli-
dae[16,17]. Since it lacks the skull character we believe that
more material is needed to discuss its phylogenetic posi-
tion. The discovery of Haopterus represents the first un-
controversial pterodactylid pterosaur in Asia, it also ex-
tends the distribution of this family to the Early Creta-
Dendrorhynchoides is another pterosaur that has
been described from the lower Yixian Formation at the
same locality as Haopterus in western Liaoning. It pre-
served a very crushed skull containing no diagnostic
characters. It was referred to Rhamphorhynchoidea.
Although it still preserved a few primitive characteristics
such as the short metacarpals it also has many more de-
rived characteristics such as the long wing digit, etc. Its
phylogenetic position remains a mystery.
Haopterus was collected from the Jianshangou Bed
of the lower Yixian Formation, it is the lower fos-
sil-bearing bed of the Jehol Biota. Associated with this
pterosaur are important fossil vertebrates[1,2,18] including
Lycopterus, Psittacosaurus, several feathered thero-
pods, and Confuciusornis. 40Ar/39Ar dating of the
single crystal sanidine from the horizon resulted in an age
of (124.6 0.3) Ma — (124.6 0.2) Ma, therefore it
should be referred to the late Valanginian (age of Juras-
sic/Cretaceous boundary is 136 Ma) or the middle Barre-
mian (Jurassic/Cretaceous boundary 144 Ma). The ver-
tebrate assemblage also suggests an Early Cretaceous
Among the pterosaurs known from the Jianshangou
Bed of the lower Yixian Formation in Sihetun areas,
western Liaoning, Dendrorhynchoides was collected at the
Zhangjiagou locality, which is the lowest fossil-bearing
horizon of the lower Yixian Formation, Haopterus was
collected from 18(6) of the excavation section[1,2] of local-
ity 1 of Sihetun which is about 5.5m higher than Den-
drorhynchoides, Eosipterus was collected from the Tuan-
shanzi locality, the horizon of which is higher than the
The pterosaur assemblage in the lower Yixian For-
mation is more advanced than that of the Late Jurassic
(Tithonian) in Solnhofen, Germany. It, however, bears a
lot resemblance to that of the Early Cretaceous (Ap-
tian-Albian) Santana Formation in Brazil. We believe
that the Valanginian or Barremian age derived from iso-
tope dating[2,19] is consistent with the pterosaur assem-
blages as well as other vertebrate assemblages of the
lower Yixian Formation.
Pterodactyloid pterosaurs occurred abundantly in the
Early Cretaceous deposits in northern China, Mongolia
and former Russia[13,21,22]. Most notable among them are
Huanhepterus of the Huanhe Formation from the Ordos
Basin and Dsungeripterus of the Tugulu Group from
the Junggar Basin of Xinjiangand Tsagantsab Forma-
tion from Mongolia. These Early Cretaceous pterosaurs
belong to Pterodactyloidea.
In summary, members of the Pterodactylidae are
previously known only in the Late Jurassic (Kim-
meridgian-Tithonian) in Europe and Africa. Haopterus
represents the first occurrence of an non-controversial
pterodactylidae in the terrestrial Early Cretaceous deposit
in Asia. Therefore this family had existed longer than pre-
viously known. The discovery of Haopterus also provides
Chinese Science Bulletin Vol. 46 No. 13 July 2001 1117
new evidence for the study of the global stratigraphic cor-
relations of the Late Jurassic and Early Cretaceous depos-
Acknowledgements We thank members of the Liaoxi Expedition
Team of the IVPP for various supports. Profs. Meemann Chang, Zhou
Zhonghe (IVPP) and Dr. Miao Desui (Natural History Museum, Univer-
sity of Kansas) read the manuscript and provided valuable suggestions.
Zhou Zhonghe improved the English version of the manuscript. We also
thank Li Yutong for preparing the specimen, Zhang Jie the photos and
Huang Jinlin the illustration. This work was supported by the Chinese
Academy of Sciences (Grant Nos. KZ951-B1-410 and KZCX3-J-03), the
Major Basic Research Project of the Ministry of Science and Technology
of China (Grant No. G2000077700), the National Natural Science
Foundation of China (Grant Nos. 49832002 and J9930095) and K. C.
Wong Education Foundation, Hong Kong.
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(Received February 13, 2001)