Extraordinarily Thick-Boned Fish Linked to the Aridification of the Qaidam Basin (Northern Tibetan Plateau)

Extraordinarily thick-boned fish linked to the aridification of the Qaidam Basin (northern Tibetan Plateau)

Meemann Chang*†, Xiaoming Wang‡, Huanzhang Liu§, Desui Miao¶, Quanhong Zhaoʈ, Guoxuan Wuʈ, Juan Liu*, Qiang Li*, Zhencheng Sun**, and Ning Wang*

*Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, P.O. Box 643, Beijing 100044, China; ‡Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, CA 90007; §Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; ¶Natural History Museum and Biodiversity Research Center, University of Kansas, Lawrence, KS 66045; ʈLaboratory of Marine Geology, Tongji University, Shanghai 200092, China; and **Department of Earth Sciences, China University of Petroleum–Beijing, Beijing 102249, China

Communicated by Peter R. Crane, University of Chicago, Chicago, IL, June 27, 2008 (received for review October 10, 2007)

Scattered with numerous salt lakes and Ϸ2,700–3,200 m above sea Holotype. Nearly complete skeleton, only with posterior part of level, the giant Qaidam inland basin on the northern Tibetan the caudal fin and a small anterodorsal portion of the body Plateau has experienced continuing aridification since the begin- missing, IVPP V 15244, from locality CD0649, Fig. 3 A–C. ning of the Late Cenozoic as a result of the India–Asia plate collision Included material. V 15012, nearly complete skeleton with the tail, and associated uplift of the Tibetan Plateau. Previous evidence of a short portion between the body and head, and the snout aridification comes mainly from evaporite deposits and salinity- missing (Figs. 1 A and B and 3D) from locality CD0507; V tolerant invertebrate fossils. Vertebrate fossils were rare until 15245.1 and V 15245.2, both are middle part of the fish skeleton, recent discoveries of abundant fish. Here, we report an unusual from locality CD0649; V 15306.1–37, detached bones of head cyprinid fish, Hsianwenia wui, gen. et sp. nov., from Pliocene lake and body, V 15307.1–50, detached pharyngeal teeth, from deposits of the Qaidam Basin, characterized by an extraordinarily localities CD0506 and CD0507. thick skeleton that occupied almost the entire body. Such enor- Etymology. The genus and species name is dedicated to the late mous skeletal thickening, apparently leaving little room for mus- Prof. Hsianwen Wu, who made great contributions to the study cles, is unknown among extant fish. However, an almost identical of the Chinese cyprinids. condition occurs in the much smaller cyprinodontid Aphanius Horizon and localities. Localities CD0504–0507, CD0641–0653, crassicaudus (Cyprinodonyiformes), collected from evaporites ex- CD0663–0666, upper part of the Shizigou Formation, Yahu Anticline, Qaidam Basin, Qinghai Province, China, N37°44Ј38Љ– posed along the northern margins of the Mediterranean Sea Ј Љ Ј Љ Ј Љ during the Messinian desiccation period. H. wui and A. crassicaudus 46 22 , E93°36 55 –38 38 ; Pliocene. Diagnosis. both occur in similar deposits rich in carbonates (CaCO ) and Schizothoracine with a unique combination of charac- 3 ters shared with barbines and primitive schizothoracines on one sulfates (CaSO ), indicating that both were adapted to the extreme 4 hand and specialized schizothoracines on the other: body elon- conditions resulting from the aridification in the two areas. The gated, nearly cylindrical; head relatively long; orbit small, situ- overall skeletal thickening was most likely formed through depo- ated anteriorly; anterior margin of lower jaw shovel-like; pha- sition of the oversaturated calcium and was apparently a normal ryngeal bone stout, triangle-shaped, with three rows of feature of the biology and growth of these fish. cylindrical teeth, new teeth with rounded top, worn teeth with truncated, flat grinding surface; distal end of transverse process ncreasing evidence ascribes a profound climatic shift, such as of 4th vertebra blunt and slightly expanded; fork in pelvic bone IAsian monsoon systems and widespread aridification, to the shallow, both branches comparatively broad; dorsal fin with uplift of the Tibetan Plateau caused by the India–Asia plate three unbranched and seven branched rays, the longest un- collision during the Late Cenozoic. The cyprinid fish reported branched ray with robust serrations; proximal portion of epural here (Fig. 1) are from the lacustrine deposits of the Pliocene expanded. Shizigou Formation in the northeastern wing of Yahu Anticline, Description and remarks. The body (Figs. 1 A and B and 3A)is Qaidam Basin, northern Tibetan Plateau (1) [Fig. 2A and for elongated, more or less rounded anteriorly and slightly com- more details see supporting information (SI) Fig. S1], collected pressed posteriorly. The standard length in the holotype V 15244 from 20 localities in a 220-m-thick sequence of siltstones, fine is 5.4 times that of the body depth (78 mm). The head is relatively sandstones, and marls under a marker bed, Horizon K (2) (Fig. long (110 mm), 1.7 times its depth (65 mm), and nearly a quarter 2B). The deposits are rich in carbonates (CaCO3) and sulfates of the standard length. All specimens, including the disarticu- (CaSO4). The unusually thick-boned fish represents an adaptive lated bones, are comparatively large. The holotype V 15244 has mode unknown in any extant fish and extremely rare in fossils. a standard length (length from the tip of snout to base of caudal Based on this fossil fish, our morphological description and fin) of 425 mm, whereas the estimated standard length of V Ϸ cladistic analysis shed light on schizothoracin phylogeny. We also 15012 is 445 mm. Body length with the caudal fin is estimated suggest that the overall skeletal thickening was formed through as 450–500 mm. Judged from the preserved parts of the body, V deposition of the oversaturated calcium and reflects the fish’s 15245.1 and V 15245.2 must have been even larger. The growth dramatic physiological adjustment to severe environmental dis- tress. The fish thus witnessed the process of aridification and Author contributions: M.C. and X.W. designed research; X.W. led the expeditions; M.C., provided a convincing link between environmental changes on H.L., J.L., Q.L., and N.W. performed research; M.C., H.L., Q.Z., G.W., and Z.S. analyzed data; the Tibetan Plateau and biological responses of its inhabitants. and M.C. and D.M. wrote the paper. The authors declare no conflict of interest. Systematic Paleontology †To whom correspondence should be addressed. E-mail: [email protected]. Ostariophysi Sagemehl, 1885. Cypriniformes Bleeker, 1860; Cyp- This article contains supporting information online at www.pnas.org/cgi/content/full/ rinidae Bonaparte, 1837; Schizothoracinae Berg, 1912; Hsian- 0805982105/DCSupplemental. wenia wui, gen. et sp. nov. © 2008 by The National Academy of Sciences of the USA

13246–13251 ͉ PNAS ͉ September 9, 2008 ͉ vol. 105 ͉ no. 36 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0805982105 Downloaded by guest on September 30, 2021 Fig. 1. H. wui gen. et sp. nov. (A) Body without head and tail (IVPP V 15012) in right view. (B) The same specimen in left view, revealed by CTScan, flipped horizontally. (C) Gymnocypris przewalskii Kessler, radiograph of body in right view. (D) box area in C in higher magnification. (E) A. crassicaudus (Agassiz), middle portion of body in left view, after Gaudant (25). (Scale bars: 30 mm in A–C);3mminE.) an, anal fin; ds, dorsal fin spine; epn, epineurals; epp, epipleurals; hs, haemal arches and spines; ns, neural arches and spines; ptr, pterygiophores; ri, ribs; ver, vertebrae.

rate of recent schizothoracines is very slow. Those with a body goid, leaving no opening between them (Fig. 3C). The ectoptery- EVOLUTION length 400 mm typically have an age of at least 9–10 years (3). goid is deep and narrow. The pharyngeal bone is stout and Thus, most of these schizothoracines were probably 10 (or even triangle-shaped (Fig. 3E). There are three rows of teeth on each 15) years old. bone, with a pattern of 2.3.5–5.3.2. The teeth are cylindrical in The structure of the skull roof, the opercular system, and the shape; new teeth have rounded top, whereas the worn teeth are palate is similar to that of other cyprinids. Judged from the truncated with flat grinding surface (Fig. 3F). position of the infraorbital bones, the orbit is quite small and The total number of vertebrae (Ϸ46) is greater than in situated rather anteriorly. The postorbital distance (distance primitive barbines. The dorsal fin has three unbranched and between posterior margin of opercle and posterior margin of seven branched rays. The posterior edge of the longest un- SCIENCES orbit) is long, more than four times that of the antorbital distance branched ray is equipped with gross serrations (Figs. 1A and 3A). ENVIRONMENTAL (distance between the anterior margin of the orbit and tip of The anal fin has three unbranched and five branched rays. The snout) (Fig. 3C). Among recent schizothoracines, those living in posterior edge of the longest unbranched ray is smooth. The broad rivers or lakes often use the caves beneath the sod-held pelvic fin is situated more posteriorly than in primitive barbines. bank edges as refuge during their winter hibernation. In summer, Its origin is under the 5th dorsal fin ray. The fork in the anterior they also hide in the caves during the day, and only come out at part of the pelvic bone is less than half of the main part of the dusk to search for food (3). It is therefore likely that their eyes bone, and both branches are broad. The structure of the caudal became reduced and their sight weakened, like some cave-living skeleton (Fig. 3B) resembles that of most cyprinids. The usually barbines today. slender, singular epural of cyprinids is widely expanded in this The mouth is subterminal, with the upper jaw protruding fish (Fig. 3B). beyond the lower (Fig. 3C). A shovel-like anterior margin of the The most striking aspect of the fish specimens from the Yahu dentary was apparently covered with a horny sheath when the Anticline is that almost all bones from the skull, paired fin fish was alive and is related to the habit of feeding on algae girdles, vertebrae with their arches and spines, pterygiophores, attached to the bottom. As in most cyprinids, the anterior and even all intermuscular bones and gill rakers (Figs. 1 A and process of premaxilla and coronoid process of the dentary are B and 3 A–I), are extremely thickened. On specimen V 15012, the well developed. The quadrate has a very shallow notch for ribs and epineurals in anterior portion of the body grow so close articulation of symplectic and is in contact with the metaptery- to each other that the vertebrae in this region are completely

Chang et al. PNAS ͉ September 9, 2008 ͉ vol. 105 ͉ no. 36 ͉ 13247 Downloaded by guest on September 30, 2021 plete specimens from the Neogene Dingqing Formation of Lunbola Basin, northern Tibet, that are similar to schizothoracines were described as a new genus and species Plesioschizo- thorax macrocephalus and referred to the Cyprinidae (16). Incomplete pharyngeal bones and disarticulated pharyngeal teeth have also been reported from early Oligocene to early Pliocene deposits of East Kazakhstan, the mountainous region of Altai, and Mongolia (17). Information about these fossils remains sketchy. They indicate the presence of possibly related fish in these areas during earlier time intervals. The Yahu schizothoracines are the best preserved to date. The localities where they occur and the Eboliang locality, where unidentified disarticulated fish bones were found, are just outside the distribution of the extant schizothoracines. To examine the phylogenetic position of H. wui, we compiled a dataset with 12 taxa and 32 characters (see Table S1). The 12 taxa include 7 extant schizothoracines and 2 fossil forms, plus 3 cyprinin and barbinin genera serving as outgroups. Characters were taken mainly from the literature (14, 15), augmented with our own observations of both extant and fossil forms. The phylogenetic analysis using PAUP Version 4.0b 10 (18) resolves Plesioschizotho- Fig. 2. Localities and section. (A) The studied area, Yahu and Eboliang in rax macrocephalus and H. wui among the early branching schizo- Qaidam Basin. (B) Yahu section, numbers to the left of the column, thickness thoracines, in a position slightly more derived than Schizothorax. of the section; numbers to the right of the column, the numbers of the The remaining schizothoracines retain positions indicated by pre- relevant localities. CD, Chaidam (Qaidam), in the numbering system used by vious authors (Fig. 4; see also SI Text). In this case, the two fossil Wang et al. (2). (Scale bar: 1,000 km.) forms, H. wui and Plesioschizothorax macrocephalus, are not the most ancient members of the group; they are somewhat in between the primitive members of the group, e.g., the extant genus Schizo- covered by them and cannot be seen from the lateral side (Fig. thorax and more derived members. The history of the group would 1 A and B). The parapophysis of the 4th vertebra is very robust go back to a time earlier than the Neogene. Our analysis shows that (Fig. 3G), whereas parapophyses of other vertebrae are also very schizothoracines form a monophyletic group within the Barbinae thick and often preserved in disarticulated state. This makes (sensu lato) (11, 13) indicating that the Barbinae sensu stricto (11, 12, many isolated bones look odd and difficult to recognize at first 19) is paraphyletic. glance (Fig. 3 G–I). The bones in V 15244 (the smallest among the available specimens) are obviously thinner than those in Interpretations of the Skeletal Thickening. Swollen or partially swol- three larger specimens V 15012, V 15245.1, and V 15245.2 len bones are not uncommon in recent tropical and subtropical (compare Fig. 1 A and B, Fig. 3A, and Fig. S2). This indicates that marine teleosts and are observed in taxonomically diverse groups the thickness of the bone appears to increase with age. (20). The phenomenon is referred to as hyperostosis (21), that is, the usually thin bones or parts of bones expand into rounded, bulky Results and Discussion structures. The swollen parts only occur in a few bones in the same Phylogenetic Position of H. wui. H. wui resembles barbines and fish (see Fig. S3), and although their location varies from species to primitive schizothoracines (Cyprinidae) in many respects and, at species, they always occur on the same bones in a given species (20, the same time, shares a few characters with some specialized 21). Similar structures have also been reported in fossil fish from schizothoracines. The schizothoracines [Schizothoracin lin- Europe, North America, and Africa, known as ‘‘Tilly Bones’’ ϭ eage Oreininae, Cyprininae (4), Tribe Oreinini, Cyprininae (21–23), and are presumed to have been caused by disease or aging (5), Cyprinidae] are endemic to the aquatic systems of the (21) or by abnormal hydrochemical conditions, such as high content Tibetan Plateau and surrounding areas (including southwestern of fluorine in the water (24). China, Kazakhstan, Kyrgyzstan, Tajikistan, Afghanistan, Paki- The overall thickening of the skeleton in the Yahu schizotho- stan, India, Nepal, and Bhutan) (5–8). The Cyprinidae are the racine H. wui is not comparable with that in the recent marine largest and most widespread group of freshwater fish and are of fishes nor is it comparable with the ‘‘Tilly bones’’ of other fossils. considerable significance in fisheries. They comprise 2,420 spe- A similarly thickened skeleton has been observed only in the cies (9) distributed on all continents except Australia, South cyprinodont fossil Aphanius crassicaudus (Fig. 1E) recovered America, and Antarctica. Although the group has been studied from the late Miocene Messinian evaporites exposed along the for nearly two centuries, views about its subdivision still diverge. northern coast of the Mediterranean (southeastern Spain, Sicily, Schizothoracines are regarded as either a subfamily of the and Crete) (25–27). A. crassicaudus was first described as a fossil Cyprinidae (6, 10–12) or a monophyletic lineage within the species of the extant genus Lebias and later reassigned to the subfamily Cyprininae (sensu lato, including the Barbinae) (4, 5) fossil genus Pachylebias (25). It is now referred to as the genus or Barbinae (sensu lato) (9, 13). The origin and diversification of Aphanius (27), an extant multispecies genus that has a circum- schizothoracines is thought to be closely related to the uplift of Mediterranean distribution and is adapted to varying degrees of the Tibetan Plateau. The recent schizothoracines have been salinities (25). The authors referred to the bone hypertrophy as divided into three categories: primitive, specialized, and highly pachyostosis. specialized, based on the extent of modifications of their scales, Although the two known pachyostotic species, H. wui and A. barbells, and rows of pharyngeal teeth and their distribution at crassicaudus, are of different age (Pliocene and late Miocene three successive altitudes at which water temperature and pre- respectively) and are from different environments (lacustrine cipitation decrease, and solar radiation and evaporation increase versus marine or lagoonal), they share many features in common. (8). Phylogenetic studies of the Schizothoracinae using cladistic Both show an overall thickening of skeleton, which is not known method have arrived at similar conclusions (14, 15). in any other fish. This thickening apparently had little adverse Fossil schizothoracines are extremely rare. Relatively com- influence on the life of the fish, and all individuals seem to have

13248 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0805982105 Chang et al. Downloaded by guest on September 30, 2021 Fig. 3. H. wui gen. et sp. nov. (A) Holotype (IVPP V 15244) in right view. (B) Caudal skeleton of holotype in right view. (C) Head of holotype in right view. (D) Ossified gill rakers (IVPP V 15012). (E) Pharyngeal bone with teeth in ventromedial view (IVPP 15245.1). (F) Four pharyngeal teeth, top view, showing grinding surface (left) and posterior view (right) (from left to right: IVPP V 15307.2, 7, 4, 14). (G) Left parapophysis of 4th vertebra in ventromedial (left) and dorsolateral (right) view (IVPP V 15306. 33). (H) Two disarticulated epineurals (left, IVPP V 15306.20; right, IVPP V 15306.18). (I) Disarticulated epipleural (IVPP V 15306.19). (Scale bars: 20 mm in A and C;10 mm in B, E, G, H, and I;5mminD and F.) an, anal fin; d, dentary; ds, dorsal fin spine; ect, ectopterygoid; ent, entopterygoid; ep, epural; epn, epineurals; epp, epipleurals; fr, frontal; hs, haemal arches and spines; hy, hyomandibular; iop, interopercle; io, infraorbitals; mpt, metapterygoid; mx, maxilla; ns, neural arches and spines; op, opercle; pa, parietal; pop, preopercle; pmx, premaxilla; ptr, pterygiophores; q, quadrate; ri, ribs; un, uroneural; ver, vertebrae.

lived a relatively long, and normal, life (growing to more than more soluble sodium chloride and other minerals deposited later half a meter long in the case of H. wui) even with increasingly in more central part of the basin. In the deposits of the Yahu thickened skeleton. In both cases, thickening of bones seems to Anticline, carbonate ooliths and crystals of gypsum are often appear when the fish reached a certain size (or age) and increases seen in the rock samples, also documenting a high concentration EVOLUTION with increasing size (or age). The timing of bone thickening in of calcium. Geological evidence also suggests that both taxa A. crassicaudus varies from locality to locality (26). Although we survived for a significant period. The Ϸ220-m-thick fish-bearing do not have specimens of H. wui smaller than 445 mm in length sediments from the Yahu Anticline indicate that Hsianwenia (V 15244), we did notice that the larger the fish the more existed for a period of up to 200,000 years (2) (Fig. 2B) before pronounced the degree of the bone thickening. Hence, it is a phase of general desiccation, although the Mediterranean area conceivable that the bones in H. wui might not have been was later flooded by the Atlantic marine water, whereas the

thickened at all when the fish was below a certain size. Qaidam Basin went on to develop into an arid badland. SCIENCES

The fish fauna associated with both species at most localities The palynological assemblage recovered from the fish- ENVIRONMENTAL is dominated by one species, suggesting unfavorable conditions bearing deposits from the Yahu Anticline, mainly includes for a more diversified fish fauna to survive. Perhaps restricted Picea, Abies, Pinus, Artemisia, Chenopodiaceae, and Gra- movement resulting from the thickened bones may not have been mineae, and documents a vegetation closely similar to that of disadvantageous because of the lack of predators in the envi- arid area of northwestern China today. Pediastrum, an alga ronment. It may also be significant that the recent relatives of usually widespread in shallow freshwaters, is also frequently both H. wui and A. crassicaudus, various species of Aphanius and observed. In the deposits of Eboliang, there is a high percent- some schizothoracines (e.g., Gymnocypris przewalskii), live in age of Typha (82.9%), a plant often seen along the margin of varied salinities (euryhaline), from water with high salinity to lakes and rivers in northern China (see SI Text and Table S2). brackish or even completely fresh water. Ostracods from the fish-bearing strata are Ilyocypris bradyi, The geological occurrence of H. wui and A. crassicaudus is also Eucypris sp., Leucocythere mirabilis, and Microlimnocythere similar. Both were collected from deposits rich in marl (CaCo3) reticulata. The first is a freshwater species, whereas the re- and gypsum (CaSo4), indicating similar hydrochemical condi- maining species are typical brackish forms. Ilyocypris bradyi, tions with a high calcium content. A. crassicaudus occurs in certain species of Eucypris, and Leucocythere mirabilis inhabit marl–gypsum along the coastal region of the Mediterranean the present day Qinghai Lake just to the east to our fossil fish deposited during the Messinian Salinity Crisis (28), where the localities. The present Lake Qinghai has a salinity of 14‰ and less soluble carbonates and sulfates precipitated first, and the is rich in magnesium sulfate. The content of sodium chloride

Chang et al. PNAS ͉ September 9, 2008 ͉ vol. 105 ͉ no. 36 ͉ 13249 Downloaded by guest on September 30, 2021 Guinas in northern Namibia. In this case, hyperostosis was attributed to the environmental induction rather than to genetic reasons. The lake water has very high calcium carbonate content (calcium hardness, as CaCO3, 185 ppm). Obser- vations on four specimens of T. guinasana originally derived from wild-caught parents but spawned and raised in laboratory tap water (calcium hardness, as CaCO3, Ϸ45 ppm) show that their roofing bones are thinner than those of wild con- specifics (29). Under natural condition, when the concentration of calcium is high, the amount of other minerals also tends to be higher than usual. Therefore, only euryhaline fishes are able to survive for a relatively extended period. Both H. wui and A. crassicaudus were the only species surviving high salinity, but they were probably also able to deposit the oversaturated calcium in their bones and thus form the overall thickened skeleton. The physiological mechanism by which the overdeposition of the calcium in the bones occurs remains to be established. Fig. 4. Cladogram showing the phylogenetic position of H. wui gen. et sp. In the Upper Youshashan Formation (stratigraphically un- nov. among schizothoracines and related taxa. derlying the Shizigou Formation) in the Eboliang area, where Typha constitutes 82.9% of the total pollen count, indicating a freshwater or low-salinity environment (Table S2), the disarticulated fish bones are normal, not thickened at all. In is the highest (66%), whereas MgSO4 comes second (20%). the area of the Yahu Anticline, overlying the fish-bearing Despite this relatively high salinity, but perhaps because of the Shizigou Formation, is the Qigequan Formation, in which no moderate calcium content, the single schizothoracin species remains of fish have been found. Instead, layers of pure now living in the lake, G. przewalskii, has normal skeletons gypsum are clearly visible. The transition from the Upper without any thickened bones (Fig. 1 C and D). Similarly, Youshashan Formation with normal-boned fossil fish, to the radiographs of a dozen specimens of the extant species A. Shizigou Formation with thick-boned fish and then to the iberus showed no abnormal bone thickening, although the barren Qigequan Formation, appears to show progressive specimens were collected from the drained surface of a salt aridification in the area during the Late Cenozoic. This lake Sebkha-el-Melah in the Sahara and preserved in salt unusually thick-boned fish was apparently an eyewitness to, or (NaCl) (26). Thus, high salinity alone without a high concen- perhaps a victim of, the drying of Qaidam Basin. tration of calcium may not cause bone thickening. Several interpretations have been presented for the skeletal Materials and Methods thickening in A. crassicaudus (25, 26), including aging, regu- Most of the fish remains reported here are from the lacustrine deposits of lation of equilibrium related to unstable salinity, high content the Pliocene Shizigou Formation in the northeastern wing of Yahu Anti- of particular chemical elements in the water, or a combination cline, Qaidam Basin. Most of the material consists of disarticulated bones of a number of these factors. Based on comparison with H. wui, and pharyngeal teeth, but two nearly complete and two partially preserved high content of particular chemical elements in the water skeletons were also recovered (localities CD0507 and CD0649). A few seems to be the most likely explanation. And because of disarticulated, nonthickened fish bones were also recovered from the growth of fish appears to have been unaffected, the chemical latest Miocene to early Pliocene Upper Youshashan Formation exposed in elements should at least meet two prerequisites: (i) they are the axis of Eboliang Anticline in the centrowestern area of the Basin harmless to the fish and (ii) they can form a component of the (Fig. 2B; for more details see Fig. S1). Fish specimens were prepared bone. mechanically. A high concentration of calcium in the water of the two areas ACKNOWLEDGMENTS. We thank J. Gaudant for sharing personal observa- where H. wui and A. crassicaudus lived was most probably the tions, references, and interesting insights; W. F. Smith-Vaniz for allowing us to crucial chemical element causing the bone thickening. In both use figure 1B in Smith-Vaniz et al. (1995); F. Meunier and E. Sychevskaya for cases, concentrations of carbonate (CaCO3) and sulfate discussions; E. M. Friis and three other anonymous reviewers for their critical review of the manuscript and helpful suggestions; Z. D. Qiu for providing (CaSO4) were apparently high. Calcium is the main component precious fossils; F. C. Zhang and W. Gao for help in preparation of illustrations; of the bone, and it is not harmful, or at least not lethal, to fish and Z. Wang for preparing fossils. This work was supported by the National in general. This is supported by the thickened cranial bones Natural Science Foundation of China (40432003) and the U.S. National Science described for the cichlid Tilapia guinasana, endemic to Lake Foundation (CToL EF0431326 and EAR-0446699).

1. Zhang PX (1987) Salt lakes of Qaidam Basin (Science Press, Beijing), pp 1–242 (in 7. Hora SL (1953) Fish distribution and Central Asian orography. Curr Sci 22:93–97. Chinese). 8. Cao WX, Chen YY, Wu YF, Zhu SQ (1981) Origin and evolution of Schizothoracine fishes 2. Wang XM, et al. (2007) Vertebrate paleontology, biostratigraphy, geochronology, and in relation to the upheaval of the Qinghai-Xizang Plateau. Studies on the Period, paleoenvironment of Qaidam Basin in northern Tibetan Plateau. Palaeogeogr Palaeo- Amplitude and Type of Uplift of the Qinghai-Xizang Plateau, ed The comprehensive climatol Palaeoecol 254:363–385. scientific expedition to the Qinghai-Xizang Plateau, Chinese Academy of Sciences 3. Tsao WS, Wu HW (1962) An investigation of the fish biology and fishery problems in (Science Press, Beijing), pp 118–130 (in Chinese). Ganze-Apa region of western Szecguan Province. Acta Hydrobiol Sin 2:79–110 (in 9. Nelson JS (2006) Fishes of the World, 4th Ed (Wiley, New York), pp 139–148. Chinese). 10. Wu XW (1964) The Cyprinid Fishes of China (Shanghai Science and Technology Press, 4. Howes G (1991) Systematics and biogeography: An overview. Cyprinid Fishes, System- Shanghai), Vol 1, pp 1–228 (in Chinese). atics, Biology and Exploitation. Fish and Fisheries Series, eds Winfield IJ, Nelson JS 11. Baña˜ rescu P (1992) Distribution and dispersal of freshwater animals in North America (Chapman & Hall, New York), Vol 3, pp 1–33. and Eurasia. Zoogeography of Freshwaters (Aula, Wiesbaden, Germany), Vol 2, pp 5. Kullander SO, Fang F, Delling B, Åhlander E (1999) The fishes of the Kashmir Valley. 512–1091. River Jhelum, Kashmir Valley. Impacts on the Aquatic Environment, ed Nyman L 12. Yue PQ, et al. (2000) Fauna Sinica, Osteichthys, Cypriniformes (Science Press, Beijing), (Swedmar, Go¨teborg, Sweden), pp 99–168. Vol 3, pp 273–390 (in Chinese). 6. Berg LS (1912) Fauna of Russia and Adjacent Countries (Imperial Academy of Sciences, 13. Cunha C, Mesquita N, Dowling TE, Gilles A, Coelho MM (2002) Phylogenetic relationships St. Petersburg, Russia), Vol 3, pp 369–704. of Eurasian and American cyprinids using cytochrome b sequences. J Fish Biol 61:929–944.

13250 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0805982105 Chang et al. Downloaded by guest on September 30, 2021 14. Wu YF (1984) Systematic studies on the cyprinid fishes of the subfamily Schizothoraci- 23. Schlu¨ter T, Kohrling R, Mehl J (1992) Hyperostotic fish bones (‘‘Tilly Bones’’) from presumably nae from China. Acta Biol Plateau Sin 3:119–140 (in Chinese). Pliocene phosphorites of the Lake Manyara area, northern Tanzania. Palaöntol Z 66:129–136. 15. Chen YF (1998) Phylogenetic and distributional patterns of subfamily Schizothoracinae 24. Schlu¨ter T, Kohring R (2002) Paleopathological fish bones from phosphorites (Pisces: Cyprinidae) I. The phylogenetic patterns. Acta Zootaxon Sin 23 supple- of the Lake Manyara area, northern Tanzania—fossil evidence of a physiological ment:17–25 (in Chinese). response to survival in an extreme biocenosis. Environ Geochem Health 16. Wu YF, Chen YY (1980) Fossil cyprinid from the late Tertiary of North Xizang, China. 24:131–140. Vertebr Pal Asiat 18:15–20 (Chinese). 25. Gaudant J (1979) ‘‘Pachylebias’’ crassicaudus (Agassiz) (Poisson Te´le´ osteén, cyprin- 17. Sytchevskaya EK (1989) Neogene freshwater fish Fauna of Mongolia. Transact Joint odontiforme), un constituant majeur de l’ichthyofaune du Messinien continental du Soviet–Mongolian Palaeotol Expedition 39:77–82. bassin me´diterraneén. Geobios 12:47–73. 18. Swofford DL (2000) PAUP*. Phylogenetic Analysis Using Parsimony (*and Other Meth- 26. Meunier FJ, Gaudant J (1987) Sur un case de pachyostose chez un poisson du Mioceńe ods) Version 4.0b (Sinauer Associates, Sunderland, MA). terminal du bassin me´diterraneén, Aphanius crassicaudus (Agassiz), (Teleostei, Cypri- 19. Wu XW (1977) The Cyprinid Fishes of China (Shanghai People’s Press, Shanghai), Vol nodontidae). C R Acad Sci Paris (Se´r 2) 305:925–928. 2, pp 229–383 (in Chinese). 27. Sorbini L, Tirapelle R (1979) Messinian fossil fish of the Mediterranean. Palaeogeogr 20. Smith-Vaniz WF, Kaufman LS, Glowacki J (1995) Species-specific patterns of hyperos- Palaeoclimatol Palaeoecol 29:143–154. tosis in marine teleost fishes. Mar Biol 121:573–580. 28. Hsu¨KJ, Ryan WBF, Cita M-B (1973) Late Miocene desiccation of the Mediterranean. 21. Konnerth A (1966) Tilly bones. Oceanus 12:6–9. Nature 242:240–244. 22. Hewitt RA (1983) Teleost hyperostose; a case of Miocene problematica from Tunisia. 29. Greenwood PH (1992) A redescription of the uniquely polychromatic African cichlid Tertiary Res 5:63–70. fish, Tilapia guinasana Trewavas. Bull Br Mus Nat Hist (Zool) 58:21–36. EVOLUTION SCIENCES ENVIRONMENTAL

Chang et al. PNAS ͉ September 9, 2008 ͉ vol. 105 ͉ no. 36 ͉ 13251 Downloaded by guest on September 30, 2021