Process Part

SCIENCE CHINA

Earth Sciences

RESEARCH PAPER April 2010 Vol.53 No.4: 485 500

doi: 10.1007/s11430-010-0048-5

Pliocene cyprinids (Cypriniformes, Teleostei) from Kunlun Pass

Basin, northeastern Tibetan Plateau and their bearings on

development of water system and uplift of the area

WANG Ning & CHANG Mee-mann*

Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology,

Chinese Academy of Sciences, Beijing 100044, China

Received November 23, 2009; accepted February 25, 2010

Here described are the cyprinid fossils from the Pliocene Lower Member of Qiangtang Formation of the Kunlun Pass Basin,

northeastern Tibetan Plateau, collected at a locality 4769 m above the sea level (asl). The materials consist of numerous disar-

ticulated and incomplete bones as well as thousands of pharyngeal teeth, fin rays, and vertebrae. The fossils were referred to

the genus Gymnocypris, lineage Schizothoracini, family Cyprinidae; the lineage Schizothoracini; and the family Cyprinidae

respectively. The Schizothoracini is a freshwater fish group endemic to the Tibetan Plateau and its surrounding area. Previous

workers on living schizothoracins regarded that Gymnocypris belongs to the highly specialized grade of the group, colonizing

higher altitudes than other members of the group. Two species are so far unequivocally assigned to the genus, i.e., G.

przewalskii and G. eckloni, and they are inhabiting Qinghai Lake and the waters on both north (the Golmud River) and south

(upper reach of the Yellow River) sides of the East Kunlun Mountain, respectively. The abundant fossil schizothoracins occur

in the Kunlun Pass Basin on the southern slope of the East Kunlun Mountain (at 4769 m asl), close to the present Golmud

River, indicating comparatively rich waters in the area and possible connections between the water systems on north and south

sides of the East Kunlun Mountain during the Pliocene. This also suggests a more humid climate in the area during the Plio-

cene than it is today. The presence of the highly specialized schizothoracin Gymnocypris may also imply less amplitude of up-

lift (approximately 1000 m) in the area since the Pliocene than previously proposed.

Gymnocypris, Schizothoracini, Pliocene, Kunlun Pass Basin of northeastern Tibetan Plateau, development of water sys-

tem, uplift of the area

Citation: Wang N, Chang M M. Pliocene cyprinids (Cypriniformes, Teleostei) from Kunlun Pass Basin, northeastern Tibetan Plateau and their bearings on

development of water system and uplift of the area. Sci China Earth Sci, 2010, 53: 485 500, doi: 10.1007/s11430-010-0048-5

The Kunlun Mountain stretches along the southern border the area that is closely linked to the uplift of the Tibetan

of Qaidam Basin, northeastern Tibetan Plateau, whereas Plateau and the global climate and environmental changes

Kunlun Pass Basin is situated on the south slope of the mid- [5, 6]. The geology of this area has long attracted the atten-

dle section of the East Kunlun Mountain (Figure 1). It is a tion of geologists and paleontologists worldwide. Paleon-

fault basin, formed at the beginning of the late Cenozoic [2, tological studies conducted in this area, however, have fo-

3]. It contains comparatively thick late Cenozoic sediments cused mainly on palynology, ostracods, and mollusks, indi-

(~700 m [4]), which documented the geological history of cating significant environmental changes since the Pliocene

[7-10]. Vertebrate fossils from the Basin have not yet been

specifically reported.

*Corresponding author (email: **********@****.**.**)

There was only one fossil fish locality known in Tibetan

Science China Press and Springer-Verlag Berlin Heidelberg 2010 earth.scichina.com www.springerlink.com

486 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 1 Geological map of East Kunlun Mountain and surrounding area, northeastern Tibetan Plateau (Based on Geological Map of Qinghai Province

[1]).

are extremely rare (Figure 2). Described so far from this

Plateau (Lunbola Basin [11]) before the team from the

area were Plesioschizothorax macrocephalus [11], a fossil

Natural History Museum of Los Angeles County (LAM)

genus and species originally referred to the family Cyprini-

and Institute of Vertebrate Paleontology and Paleoanthro-

dae; Hsianwenia wui [14], another fossil genus and species

pology (IVPP), led by Wang Xiaoming, started to work in

referred to the subfamily Schizothoracinae (=Oreininae,

Qaidam Basin, northeastern Tibetan Plateau, at the end of

Cyprinidae); and several disarticulated pharyngeal bones

last Century. Several vertebrate fossil localities, including

with teeth referred to the Barbinae [13] of the Cyprinidae.

fish remains, were found in Qaidam Basin [12 14] (Figure

Both Plesioschizothorax macrocephalus and Hsianwenia

2). During the field seasons of 2006 and 2007, the team

wui were considered as belonging to the subfamily

worked in the Kunlun Pass Basin and discovered numerous

Schizothoracinae by Chang et al. [14].

disarticulated fish bones and teeth as well as some mam-

The Cyprinidae is the largest family of freshwater fishes.

mals [17]. The fish fossils were collected from the locality

Although works abound as to the phylogeny of the group

KL0607 (35 38 09.0 N, 94 05 05.6 E), about two kilome-

during the last two decades, both from morphological and

ters east of the Qingzang Railway and 116 km southwest to

molecular aspects [18-27], views are equally abundant

Golmud City, Qinghai Province (Figure 1). The altitude of

among ichthyologists on recognition of the subgroups of the

the locality is 4769 m above the sea level (asl). This is one

family, their scope, and their interrelationships. For pos-

of the few localities uncovered recently from the Plateau

sessing the unique anal scales, schizothoracins are re-

with a large quantity of fossil fish, and it is one of the high-

garded as a monophyletic subfamily (Schizothoracinae) [16,

est vertebrate fossil localities in the world. The fish remains

28-32] or a subgroup (Schizothoracini) within the subfam-

from the Kunlun Pass Basin were collected from the Lower

Member of the Qiangtang Formation [6]. The age of the ily Cyprininae [19, 33]. For their restricted distribution,

schizothoracins usually were not included or only one spe-

Lower Member of the Qiangtang Formation is 2.58-1.77

cies was included in a number of phylogenetic analyses of

Ma based on a magnetostratigraphic study, ranges from the

the Cyprinidae or Cypriniformes [20-22, 24-27]. Because

late Pliocene to early Pleistocene according to Song et al.

of lack of specimens, the group was rarely discussed in

[6], or late Pliocene according to Wang et al. s work on

these works. Wherever more specimens of this group were

fossil mammals [17]. In this paper we adopt the view in the

involved, the group was frequently treated as monophyletic

latter work. The fish-bearing deposits are fluvial-lacustrine

dark gray mudstones intercalated with yellow brown muddy [18, 19, 31, 32, 33-37], regardless of which taxonomic rank

sandstones or siltstones. (subfamily, lineage or tribe) the group is placed at. In a few

The Cenozoic fossil fishes found from Tibetan Plateau recent works dealing with the phylogeny of the Cyprinidae,

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 2 Map of Cenozoic fossil fish localities and distribution of Recent Gymnocypris species in Tibetan Plateau, based on Wu and Wu [15] and Chen

and Cao [16].

however, schizothoracins were considered non-monophy- tion and environment. We were able to identify some of the

bones as belonging to Gymnocypris sp. indet., and a few

letic [38-41].

others to the lineage Schizothoracini gen. and sp. indet.

In most morphological and molecular studies of the Cy-

(subfamily Cyprininae). For the rest of bones, we could

priniformes and Cyprinidae, the subfamily Cyprininae [19,

only refer them to the family Cyprinidae gen. and sp. indet.

20, 26, 27] or Series Barbini [18] is well supported, and the

without any specifications.

Schizothoracini, where included, is treated as one of its

The zoogeography of the living schizothoracins has been

subgroups [19, 33]. In this paper, we follow Howes [19] and

studied and the evolutionary process of the group deduced

Kullander et al. [33] to refer the materials, which we are

[30, 42]. The living schizothoracins were considered to have

able to identify as belonging to Gymnocypris, to the

developed in correlation with the uplift of the Tibetan Pla-

Schizothoracini lineage (=Tribe Oreinini [33], Schizotho-

teau and were divided into three grades: primitive, special-

racinae [28]), subfamily Cyprininae. As for the lineage

ized, and highly specialized. The division of the three

(Tribe) name, we prefer Schizothoracini to Oreinini at pre-

grades was based on the extent of modifications of their

sent, pending further works to clarify the priority of the ge-

scales, barbells, and rows of pharyngeal teeth, and their dis-

nus name, Schizothorax or Oreinus [33]. The lineage

tribution at three successive altitudes at which water tem-

Schizothoracini is a comparatively large group with nu-

perature and precipitation decrease, and solar radiation and

merous morphologically similar genera and species. The

evaporation increase [30]. The genus Gymnocypris from our

phylogenetic relationship of the group is in need of further

materials falls in the highly specialized grade.

work.

From the numerous fish bones collected from the locality

KL0607, Kunlun Pass Basin, we could recognize fishes

1 Materials and methods

belonging to two cypriniform families, the Cyprinidae and

Nemacheilidae. In this paper, we describe the cyprinid

bones and discuss some problems concerning their distribu- All fish remains from Kunlun Pass Basin consist of disar-

488 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

ticulated, incomplete bones. They do not seem buried in situ 2 Systematic paleontology

but sorted and transported by water, then re-deposited, for

only relatively thick bones or thick parts of bones are pre- Superorder Ostariophysi Sagemehl, 1885

served. Usually the bigger and thicker bones are black to Order Cypriniformes Bleeker, 1859/60

dark brown and smaller and thinner bones light, and they Family Cyprinidae Bonaparte, 1840

stand out against the lighter-colored matrix. The specimens Subfamily Cyprininae sensu Howes, 1991

of Gymnocypris, schizothoracins, and cyprinids are num- Lineage Schizothoracini sensu Howes, 1991

bered as IVPP V 169**-*****, IVPP V 169**-*****, and (=Tribe Oreinini, Kullander et al., 1999)

Genus Gymnocypris G nther, 1868

IVPP V 169**-***** respectively.

Gymnocypris sp. indet.

Materials used for comparison include dry skeletons and

disarticulated bones of 15 species of the Schizothoracini and

Referred specimens: IVPP V 16925.1-32, anterior parts

5 species of other cyprinines. They are:

of dentaries; IVPP V 16926.1-55, posterior parts of angu-

Gymnocypris przewalskii IVPP OP 343, complete skele-

loarticulars; IVPP V 16927.1-14, ventral parts of quadrates;

ton; and IVPP OP 344, disarticulated bones;

IVPP V 16928.1-40, posterior parts of maxillae; IVPP V

G. eckloni IVPP OP 345, disarticulated bones;

Oxygymnocypris stewartii IVPP OP 346, disarticulated 16929.1-42, kinethmoids; IVPP V 16930.1, a large part of a

bones; left pharyngeal bone with teeth and bases of broken teeth,

lacking the end part of the posterior edentulous process;

Schizopygopsis pylzovi IVPP OP 347, IVPP OP 348, dis-

IVPP V 16931.1, os suspensorium; IVPP V 16932.1-7,

articulated bones;

S. stoliczkai IVPP OP 349, IVPP OP 350, disarticulated supracleithrums.

Dentary: Seventeen left and 15 right dentaries were rec-

bones;

ognized, but none of them is intact. On specimen IVPP V

S. younghusbandi IVPP OP 351, disarticulated bones;

16925.1, a large part of the left dentary is preserved, only

Platypharodon extremus IVPP OP 352, disarticulated

with its posterior part along with the posterodorsal part of

bones;

the coronoid process lacking. Its anterior branch bends

Gymnodiptychus pachycheilus IVPP OP 353, disarticu-

medially with a deep and narrow joint facet to meet its

lated bones;

counterpart. The anterior branch shows a broad and hori-

Ptychobarbus dipogon IVPP OP 354, disarticulated

zontal dorsal surface, with a foramen located at the middle

bones;

point between the joint facet and the origin of the coronoid

Schizothorax macropogon IVPP OP 355, disarticulated

process, for the passage of the mandibular branch of the

bones;

trigeminal (V) nerve. The foramen opens on the lateral sur-

S. o connori IVPP OP 356, disarticulated bones; face of the dentary closer to the upper rim of the first sen-

S. waltoni IVPP OP 357, disarticulated bones; sory canal opening than to the dorsal margin of the lateral

S. oligolepis IVPP OP 358, disarticulated bones; surface (Figure 3A). The groove accomodating the insertion

S. prenanti IVPP OP 359, disarticulated bones; of the anguloarticular and Meckel s cartilage is clearly

S. chongi IVPP OP 360, disarticulated bones; shown in the medial face of the dentary (Figure 3B). The

Barbodes schwanenfel IVPP OP 361, disarticulated most characteristic feature of the dentary is that the man-

bones; dibular sensory canal is very broad and the openings leading

from it to the surface are very large. Two and an upper half

Spinibarbus sinensis IVPP OP 362, disarticulated bones;

of the oval shaped openings can be seen in the specimen,

Balantiocheilus melanopterus IVPP OP 363, disarticu-

leading from the mandibular canal onto the ventrolateral

lated bones;

surface of the dentary. The vertical diameter of the openings

Cyprinus carpio IVPP OP 364, disarticulated bones;

is roughly comparable to the depth of the part of the lateral

Carassius auratus IVPP OP 365, disarticulated bones.

surface of the dentary above the sensory canal openings

All specimens are stored in the collections of IVPP.

(Figure 3A). The origin of the coronoid process is opposite

The fossil bones were easily picked out or screen-washed

to the posterior edge of the second sensory canal opening.

from the comparatively soft matrix and then cleaned me-

Among Recent schizothoracins, such large-sized, cavity-

chanically using a thin needle under binocular WILD- M7A

like mandibular canal openings have only been observed in

stereomicroscope. Photographs were taken by CANON 1Ds

the species of the genera Gymnocypris (Figure 3C, D) and

digital camera connected to OLYMPUS SZX12 stereomi- Oxygymnocypris (Figure 3E, F) [31]. The fossil dentary is

croscope. The way of measurements of the pharyngeal bone more similar to that of Gymnocypris than to Oxygymno-

follows Chu [43] and the terms of teeth are according to cypris. In Oxygymnocypris, the dentary is slenderer, the

Vasnetsov [44]. General osteological terminology follows dorsal side of its anterior branch is narrower, and its coron-

that of Conway et al. [45]. oid process is situated more backward (posterior to the third

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 3 Dentary of fossil Gymnocypris IVPP V 16925.1 (A, B) and Recent Gymnocypris IVPP OP 345 (C, D) and Oxygymnocypris IVPP OP 346 (E, F).

A, C, E ventrolateral view. B, D, F dorsomedial view. cp, coronoid process; fd, foramen for passage of mandibular branch of trigeminal nerve (V) in dorsal

side; fl, foramen for passage of mandibular branch of V in lateral side; gac, groove accomodating anguloarticular and Meckel s cartilage; j, joint facet for

counterpart; mo, mandibular sensory canal openings. Scale bars: 2 mm.

sensory opening) than that in Gymnocypris. And the fora- Since the narrow bone bands dividing the openings outside

men of the passage of the mandibular branch of V in the the sensory canal are broken, only wide groove instead of

lateral surface of the dentary is closer to the dorsal margin canal can be seen in our specimen (Figure 4A, B, and D).

than to the upper rim of the sensory canal openings in Oxy- Such broad sensory canal in anguloarticular, in continuation

gymnocypris. with that in dentary, has only been observed in Gymno-

Anguloarticular: Twenty-six left and 29 right anguloar- cypris among Recent schizothoracins (Figure 4E). The

ticulars were identified from our materials. Specimen IVPP anguloarticular of Oxygymnocypris bears similarly

V 16926.1 shows a well preserved right anguloarticular, developed sensory canal as that of Gymnocypris, but the

only with a small anterior part missing. It is an elongated caliber of the canal is visibly narrower (Figure 4F).

bone plate with its anterior part narrowing and stretching Quadrate: The ventral parts of eight left and six right

forward to insert into the groove on the medial side of the quadrates were found. All of the fossil quadrates lost their

dentary (Figure 4A D). Its posterodorsal part is thickened. dorsal plates, and only the specimen IVPP V 16927.1 has

On the dorsal side of this part lies the well-developed socket comparatively intact ventral part (Figure 5A, B). The ven-

for receiving the articular head of the quadrate (Figure 4A), tral part of the quadrate is shaft-like, broad and thick in the

whereas on its ventromedial side is a small articular facet front whereas narrow and thin in the rear, and tapers into a

for the retroarticular (Figure 4B). The medial face of the tip in the posterior end. The anterior articular facet for the

anguloarticular is somewhat uneven, covered with pits, anguloarticular joint socket is rather broad. The groove ac-

short grooves and ridges. The area where the Meckel s car- commodating the symplectic is clearly shown on the medial

tilage originates is clearly shown (Figure 4C). Anterior to side of the bone, and the groove stretches anteriorly close to

the base of the socket for the articular head of the quadrate, the articular facet in the front. The lateral margin of the

the bone bends slightly inwards, forming a smooth lateral bone is blade-like. The anterior portion of the dorsolateral

surface (Figure 4A, B, and D). The broad mandibular sen- surface of the bone is covered with pits and short grooves

sory canal seems traversing the bone just beneath the socket. leading backward from the pits, whereas the ventromedial

490 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 4 Anguloarticular of IVPP V 16926.1 (A D) and Recent Gymnocypris IVPP OP 345 (E) and Oxygymnocypris IVPP OP 346 (F). A, dorsal view. B,

ventral view. C, medial view. D F, lateral view. ar, articular facet for retroarticular; co, Meckel s cartilage origin; mc, mandibular sensory canal; sq, socket

for articular head of quadrate. Scale bars: 2 mm.

Figure 5 Quadrate of IVPP V 16927.1 (A, B) and Recent Gymnocypris IVPP OP 345 (C, D). A and C, dorsal view. B and D, ventral view. a, articular facet

for anguloarticular joint socket; dpl, dorsal plate; gs, groove containing symplectic. Scale bars: 2 mm.

surface of the bone is rather smooth. Although only the preserved basal part, the dorsal process is fairly broad and

ventral part was preserved, the fossil is very similar to the forms a nearly right angle with the posterior part of the bone

equivalent part of the quadrate in Gymnocypris (Figure 5C, (Figure 6A, B). The sigmoid lower margin and the

D). knob-like posterior end of the maxilla occur mostly in cy-

prinines [20]. Combination of downward bent posterior end

Maxilla: Posterior parts of 21 left and 19 right maxillae

and broad dorsal process seems most similar to that in

were found. As far as we can see from the preserved parts, it

Gymnocypris among schizothoracins (Figure 6C, D).

is a long bone, with its lower margin sigmoidally curved

and posterior end bent down and widened into a round knob. Kinethmoid: The kinethmoid is a rod-like, bisymmetrical

The anterior part of the maxilla is broken. Judged from its small bone, with its upper and lower parts expanded and

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 6 Maxilla in IVPP V 16928.1 (A, B) and Recent Gymnocypris IVPP OP 345 (C, D). A and C, lateral view. B and D, medial view. dpr, dorsal proc-

ess; pk, posterior knob. Scale bars: 2 mm.

flattened in anterior-posterior direction and its middle part

deep and narrow (Figure 7A C). There is a shallow depres-

sion in the anterior surface of its upper part for the attach-

ment of the ligament connecting the bone with the dorsal

processes of the premaxillae, whereas the rugged posterior

surface of its lower part with two tiny processes on its ven-

trolateral margin probably serves for the attachment of the

connective tissue linking it with the mesethmoid [46] and

the vomer [47]. The lateral side of the middle part is con-

cave, accommodating the cartilage linking the nasal and

preethmoid [46, 48]. From the lateral view, the dorsal mar-

gin of the bone is arc-like. The width of the upper part is

comparable to that of the lower part, and is much broader

than that of the middle part. It is impossible to look through

the kinethmoid in all species of cyprinids. From all what we

could examine, the bone at our hand is most similar to the

kinethmoid of Gymnocypris (Figure 7D F).

Pharyngeal bone: From our material we found only one

small pharyngeal bone. The bone is crescent-shaped and

relatively slender. Its anterior edentulous process, tapering

anteroventrally to a pointed tip, is comparable in length with

the dentigerous surface. If Chu s [43] method of measure-

ments is followed, the estimated length of the bone (~0.55

mm) should not be much influenced by the lack of the end

part of the posterior edentulous process. Then the length/

width (~0.19 mm) ratio of the pharyngeal bone is approxim-

ately 2.9. The dorsal edge of the bone is narrow, whereas

the ventromedial surface is broad (Figure 8A). The pitted

surface is expanded in its middle part, extending forward to

Figure 7 Kinethmoid in IVPP V 16929.1 (A C) and Recent Gymno- the point opposite to A1 (Figure 8B). The anterior angle is

cypris IVPP OP 345 (D F). A and D, front view. B and E, posterior view.

broken, and the posterior angle is not preserved. Judged

C and F, lateral view. d, depression for ligament connecting dorsal proc-

from the three preserved teeth and four bases of broken

esses of premaxillae. p, process for connective tissue linking mesethmoid

teeth observed in the bone, it can be confirmed that there

and vomer. Scale bars: 1 mm.

492 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 8 Pharyngeal bone in IVPP V 16930.1 (A, B) and Recent Gymnocypris IVPP OP 345 (C, D), Schizopygopsis IVPP OP 351 (E, F), Oxygymnocypris

IVPP OP 346 (G, H), Ptychobarbus IVPP OP 354 (I, J), and Gymnodiptychus IVPP OP 353 (K, L). A, C, E, G, I, and K, dentigerous sides; B, D, F, H, J, and

L, pitted sides. aa, anterior angle; ae, anterior edentulous process; de, dorsal edge; pa, posterior angle; pe, posterior edentulous process; vs, ventromedial

surface. Scale bars: 0.5 mm for A and B, 3 mm for C L.

are two rows of pharyngeal teeth. The four teeth in the inner (sensu Cao et al. [30]).

row (row A) are stronger than the three teeth in the outer Os suspensorium: In specimen IVPP V 16931.1, only

row (row B). The tooth formula is 3, 4 /. The preserved the outer arm of a left os suspensorium (parapophysis of the

teeth A1, B1, and B2 are elliptically cylindrical, with 4th vertebra) is preserved. The inner arm is broken, leaving

slightly recurved tips. Their spoon-like grinding surfaces are its base sticking out from the outer arm close under the

longer than wide, and flanked with lateral ridge-like edges. pyramid-like top. The outer arm is, on the whole, an elon-

B1 is slightly stronger than B2. The grinding surfaces of B1 gated arched strip with smooth surfaces, except its thick

and B2 are more oblique than that of A1 (Figure 8A). This upper head with the pyramid-like process, fitting into the

fossil pharyngeal bone is similar to that of several special- fossa on the lateral side of the 4th centrum (Figure 9A). On

ized and highly specialized Recent schizothoracin genera the posterodorsal side of the bone the area under the top is

(sensu Cao et al. [30]), e.g., Diptychus, Ptychobarbus, fenestrated (Figure 9B). The outer arm is widest at the bi-

Gymnodiptychus, Schizopygopsis, Chuanchia, Gymnocypris, furcating point of the inner arm that should have formed the

and Oxygymnocypris, based on the tooth formula (3, 4 /) suspensorium, but is missing in our specimen. From the

and spoon-like grinding surface [15, 16]. The pharyngeal bifurcating point downwards, the outer arm (or parapophy-

bone of Oxygymnocypris (Figure 8G, H) is much slenderer sis) becomes thinner and bending moderately inwards. The

than that of Gymnocypris (Figure 8C, D) and the fossil bone distal end is slightly expanded and blunt. According to Wu

(Figure 8A, B), with the length/width ratio more than 3.6 and Chen [11], the distal end of the 4th parapophysis (outer

[15, 16]. Our observation shows that the pitted surfaces in arm of the os suspensorium) in Recent schizothoracins is

Ptychobarbus and Gymnodiptychus (Figure 8I L) are much expanded (Figure 9C J), whereas those of other cyprinines

narrower than that of Gymnocypris (Figure 8C, D) and the are always narrow (Figure 9K N). Among Recent

fossil (Figure 8A, B). Furthermore, according to Chu [43], schizothoracins we have checked, the shape of the outer arm

the anterior edentulous process is rather short, only about of the os suspensorium is quite different between different

two thirds of the length of the dentigerous surface in Dip- genera (Figure 9C J), and the fossil os suspensorium is

tychus. The fossil pharyngeal bone is more similar to that of most similar to that of Gymnocypris (Figure 9C, D).

Gymnocypris (Figure 8C, D) than to that of Schizopygopsis Supracleithrum: Four left and three right supracleithrums

(Figure 8E, F), particularly in the contour of the anterior were found from our materials. The supracleithrum is a ver-

edentulous process. There are three rows of pharyngeal tical, elongated, and flattened bone, with its upper part

teeth in primitive schizothoracins and all barbines slightly bent inwards. Its uppermost part is nearly triangular

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 9 Fossil os suspensorium in IVPP V 16931.1 (A, B) and Recent Gymnocypris IVPP OP 345 (C, D), Schizopygopsis IVPP OP 351 (E), Oxygymno-

cypris IVPP OP 346 (F), Platypharodon IVPP OP 352 (G), Ptychobarbus IVPP OP 354 (H), Gymnodiptychus IVPP OP 353 (I), Schizothorax IVPP OP 357

(J), Barbodes IVPP OP 361 (K), Spinibarbus IVPP OP 362 (L), Cyprinus IVPP OP 364 (M), and Carassius IVPP OP 365 (N). A, C, and E M, front view. B

and D, back view. do, distal end of outer arm; ia, inner arm; uh, upper head. Scale bars: 0.5 mm for A and B, 2 mm for C N.

and pointed at the top. Two tiny but prominent processes must have been covered by the posttemporal bone. A

are shown at the two lower angles of the triangle. The lat- groove with an opening at its bottom can be noticed close to

eral surface of the upper part of the bone is smooth and the posterior edge of this part, transmitting the sensory canal

494 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Opercle: Seven left and 11 right anterodorsal fragments

of the opercles were identified by its prominent opercular

arm and typical articular fossa for the process at the rear

margin of the hyomandibular. The opercular arm protrudes

anterodorsally, forming an obtuse angle with the dorsal

margin of the bone. The articular fossa is situated very close

to the base of the opercular arm (Figure 11D). The lateral

surface of the opercle is generally smooth, but covered by a

few scattered openings with shallow grooves leading from

them and arranged in a radiating way from the base of the

arm (Figure 11E).

Thick spine-like fin ray: More than one thousand

well-preserved unbranched, spine-like fin rays have been

collected, and most of them are with their distal ends broken

and in left or right halves. They are strong, serrated at their

posterior edge. The serrations emerge a short distance up

the base of the fin ray, and the proximal few ones are

weaker than the distal ones. Twenty serrations are preserved

on the most completely preserved ray IVPP V 16910.1, and

the serrations stand either perpendicular to the ray or

Figure 10 Supracleithrum in IVPP V 16932.1 (A, B) and Recent Gym- somewhat with the tip pointing distally (Figure 11F, G).

nocypris IVPP OP 345 (C, D). A and C, lateral view; B and D, medial view.

These rays look like the posteriormost unbranched fin rays

sc, sensory canal. Scale bars: 2 mm.

in the dorsal fin of Recent schizothoracins. The spine-like

fin rays of similar structure were previously found in fossils

to the lateral line on the body. The broadest part of the bone, of Hsianwenia wui (Schizothoracinae) from Yahu [14] and

covered with tiny pits, is close to its upper-middle part, in Cyprinidae gen. et sp. indet. from Lulehe area, Qaidam

where the bone is bending. The lower part of the bone is Basin [13]. In some other cyprinines, such as Cyprinus,

narrow and shaft-like, covered with longitudinal thin Carassius and many other cyprinines, the spine-like fin rays

grooves (Figure 10A). The medial surface of the bone is are usually with tips of the serrations pointing proximally.

smooth (Figure 10B). Judged from the shape of the bone,

Cyprinidae gen. et sp. indet.

the ornamentation on the lateral surface, and the two tiny

processes on the medial side of the dorsalmost part, the fos- Referred specimens: IVPP V 16933.1 29, anterior parts

sil bone is most similar to the supracleithrum of Gymno- of urohyals; IVPP V 16934.1 11, ventral hypohyals; IVPP

cypris (Figure 10C, D). V 16935.1 30, anterior ceratohyals; IVPP V 16936.1 23,

posterior ceratohyals; IVPP V 16937.1 4, interhyals; IVPP

Schizothoracini gen. et sp. indet.

V 16938.1 26, posterodorsal parts of hyomandibulars;

Referred specimens: IVPP V 16908.1 1392, detached IVPP V 16939.1 4, first pectoral radials; IVPP V 16940.

pharyngeal teeth; IVPP V 16909.1 18, anterodorsal parts of 1 11, medialmost pelvic radials.

opercles; IVPP V 16910.1 1568, unbranched fin rays with Urohyal: The anterior part of the urohyal is narrow, with

serrations on the posterior edge. two long and nearly parallel anterior processes for connec-

Pharyngeal teeth: More than one thousand scattered tion of the ventral hypohyals (Figure 12A). The horizontal

pharyngeal teeth were picked out from the deposits in ventral plate is almost lost except the very anterior portion.

Kunlun Pass Basin. These teeth are of similar shape as those Only a small part of the vertical dorsal plate is preserved

on the pharyngeal bone described above, with their crowns (Figure 12B).

standing straight on the neck or slightly bent anteriorly. Tips Ventral hypohyal: Three left and eight right ventral hy-

of the teeth are curved posteriorly in different extent. The pohyals were discovered. The bone is somewhat triradiate,

spoon-like grinding surface of various widths is covered with an anteroventrally protruding process (Figure 12C, D).

with fine, longitudinal stripes (Figure 11A C). Pharyngeal Posteriorly, the bone is composed of two joint facets, the

teeth of this type are common in Recent schizothoracins [15, ventral broader one for the connection to the anterior cera-

16, 43]. Although pharyngeal teeth with spoon-like grinding tohyal and the dorsal narrower one for the dorsal hypohyal

surfaces also exist in several other cyprinin genera such as to attach. The lateral and dorsal surfaces of the bone have

Barbodes and Spinibarbus, which are closely related with scattered fossae and pits, whereas the medial surface is

schizothoracins, the pharyngeal teeth of Barbodes and comparatively smooth.

Spinibarbus are more laterally depressed and the grinding Anterior ceratohyal: Fifteen left and 15 right anterior

surfaces are narrower than that of schizothoracins. ceratohyals were unearthed. The bone is relatively thick and

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

seems in continuation with that in the anterior ceratohyal,

possibly for the hyoidean artery to traverse [45]. Its ventral

margin is blade-like. The lateral side is relatively rough,

with shallow fossae close to the posterior angle. The medial

side of the bone is almost smooth, except several tiny pits

near its posterior angle.

Interhyal: Three left and one right interhyals were ob-

tained. The bone is rod-like. Its lower end bends slightly

anteriorly with a concave facet for articulation with the

posterior ceratohyal, whereas its upper end is comparatively

flat, for articulation with the hyomandibular and symplectic

(Figure 12I, J). Close to its lower end, the posterior side of

the bone carries a ridge (Figure 12K). The lateral side of the

bone for adherence to the medial side of the preopercle is

uneven, whereas the medial side of the interhyal is com-

paratively smooth.

Hyomandibular: Seven left and 19 right posterodorsal

fragments of the hyomandibular were recognized by the

characteristic articular area with the neurocranium on top of

the bone and the rounded articular process for the opercle at

the rear margin. On the lateral side, a rather sharp ridge

stretches backward starting from a point under the opercle

process (Figure 12L). Many small pits are shown on the

medial side of the bone, and especially on a raised area an-

teroventral to the opercular process (Figure 12M). Antero-

dorsal to this area, part of a large opening can be seen,

Figure 11 Pharyngeal teeth IVPP V 16908.1 3 (A C), opercle IVPP V which usually accommodates the hyomandibular ramus of

16909.1 (D, E) and unbranched fin ray with serrations IVPP V 16910.1 (F,

the facial nerve (VII) and the efferent hyoidean artery.

G). D and F, lateral view; E and G, medial view. ah, articular fossa for

Pectoral radials: One left and three right first (outer-

hyomandibular; di, distal end; dm, dorsal margin; g, grinding surface; oa,

most) pectoral radials were found. The radial is somewhat

opercular arm; pr, proximal end. Scale bars: 1 mm for A E, 2 mm for F

and G. elongated with broad front margin, which should have at-

tached to the posteroventral side of the scapula. The poste-

of rectangular shape, with its posterior end deeper than the rior part of the bone is narrow with a rod-like end. The dor-

sal side of the bone is rugged and the ventral surface is

anterior, and middle part slightly constricted (Figure 12E, F).

comparatively smooth (Figure 12N, O). The medial surface

Its thick anterior end bears two joint facets for the two hy-

of the bone must have clung to the second pectoral radial

pohyals to attach, one facet facing front for the ventral hy-

and the lateral surface connected to the proximal end of

pohyal and the other facing medially for the dorsal hypo-

pectoral fin rays.

hyal. The posterior end of the anterior ceratohyal is com-

paratively thin, and is in connection with the posterior cera- Pelvic radials: Six left and five right medialmost pelvic

tohyal. The dorsal margin is slightly concave. Along the radials were found. The radial is roughly boomer-

margin is a groove with several pits sitting in the bottom. ang -shaped with the medial margin arc-like and the lateral

The ventral margin is deeply concave and thin, with its margin concave (Figure 12P, Q). The bone slightly bends

dorsal-ventrally. The anterior terminal of the bone is com-

middle part nearly blade-like. Both lateral and medial sur-

faces of the anterior ceratohyal are entirely covered with paratively broad, whereas the bone becomes narrower pos-

pits and shallow grooves leading from the pits towards the teriorly, with a sharp rear tip. There is a tiny notch on the

back. anterior terminal, presumably accommodating the small

process in the middle of the posterior margin of the basip-

Posterior ceratohyal: Twelve left and 11 right posterior

ceratohyal were found. The bone is triangular, with a deep terygium.

anterior margin in connection with the anterior ceratohyal

and a posterior angle (Figure 12G, H). At the very posterior

3 Discussion

end of the bone is a small process pointing posterodorsally.

The joint facet for the interhyal is situated at the postero- 3.1 Identification of fossil fish materials

dorsal edge of the bone, just in front of the process. Along

the anterior two thirds of its dorsal margin is also a narrow Part of the fossil bones unearthed form the Kunlun Pass

groove with foramina sitting in the bottom. The groove Basin is assigned to the genus Gymnocypris, based on the

496 WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

Figure 12 Fossils identified as cyprinids. A and B, IVPP V 16933.1 urohyal; C and D, IVPP V 16934.1 ventral hypohyal; E and F, IVPP V 16935.1 ante-

rior ceratohyal; G and H, IVPP V 16936.1 posterior ceratohyal; I K, IVPP V 16937.1 interhyal; L and M, IVPP V 16938.1 hyomandibular; N and O,

16939.1 first pectoral radial; P and Q, 16940.1 medialmost pelvic radial. A, C, N, and P, dorsal view; D, O, and Q, ventral view; B, E, G, I, and L, lateral

view; F, H, J, and M, medial view; K, posterior view. ahs, articular facet to hyomandibular and symplectic; an, articular area with neurocranium; apc, articu-

lar facet to posterior ceratohyal; ao, articular process for opercle; du, dorsal plate of urohyal; gha, groove accommodating hyoidean artery; jac, joint facet to

anterior ceratohyal; jdh, joint facet to dorsal hypohyal; ji, joint facet to interhyal; jvh, joint facet to ventral hypohyal; ona, opening accommodating hyoman-

dibular ramus of facial nerve and efferent hyoidean artery; pvh, processes connecting ventral hypohyals. Scale bars: 1mm for A D, I K, and N Q; 2mm for

E-H, L, and M.

following observations. The mandibular sensory canal in the the pharyngeal bone of Ptychobarbus, Gymnodiptychus, and

dentary and anguloarticular is very broad and its cavity-like Oxygymnocypris is much slenderer than in our fossils and

sensory canal pores are very large. This is typical only for Gymnocypris. The elongated kinethmoid is almost identical

Gymnocypris and Oxygymnocypris among schizothoracins. to that of Gymnocypris; the shaft-like ventral part of quad-

The dentary and anguloarticular are much deeper in Gym- rate, and the outer arm of the os suspensorium (parapophy-

nocypris and our fossils than in Oxygymnocypris. As in sis of the 4th vertebra) with its slightly expanded, blunt dis-

Gymnocypris, the supracleithrum is slender, with a small tal end are all most similar to that of Gymnocypris in many

triangular top part, carrying two small processes at the of their detailed structures (see above).

lower angles of the triangle, and a long shaft-like lower part. The numerous detached spoon-like pharyngeal teeth have

The pharyngeal bone is comparatively broad, having a tooth its grinding surface longer than wide, showing many fine

formula as 3, 4 /. Though having the same tooth formula, longitudinal stripes; the opercle has smooth outer surface

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WANG Ning, et al. Sci China Earth Sci April (2010) Vol.53 No.4

and scattered openings and grooves leading from them; and schizothoracin genera already existed in the Kunlun Pass

the thick spine-like fin ray bears distally pointing serrations Basin area during the Pliocene.

at its posterior edge. Those are the features that could all be

assigned to schizothoracins. Had we had better knowledge 3.2 Implications on development of water system and

about morphology of more schizothoracin species, we could environment

have referred these bones to specific genera, likely includ-

Recent schizothoracins are endemic to aquatic systems of

ing Gymnocypris. The rest of the bones referred to the Cy-

Tibetan Plateau and its surrounding areas, comprising

prinidae also bear general similarities to those of the

11 12 genera and nearly one hundred species and subspe-

Schizothoracini or even the Gymnocypris. We were not able

cies. The Schizothoracini is a unique group of the Cyprini-

to assign them

Contact this candidate