Freiberger Forschungshefte, C 532 psf (17) Freiberg, 2009

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1 Freiberger Forschungshefte, C 532 psf (17) Freiberg, 2009 A nearly complete skeleton of Saurichthys orientalis (Pisces, Actinopterygii) from the Madygen Formation (Middle to Late Triassic, Kyrgyzstan, Central Asia) preliminary results by Ilja Kogan, Katharina Schönberger, Jan Fischer & Sebastian Voigt, Freiberg with 5 figures KOGAN, I., SCHÖNBERGER, K., FISCHER, J. & VOIGT, S. (2009): A nearly complete skeleton of Saurichthys orientalis (Pisces, Actinopterygii) from the Madygen Formation (Middle to Late Triassic, Kyrgyzstan, Central Asia) preliminary results. Paläontologie, Stratigraphie, Fazies (17), Freiberger Forschungshefte, C 532: ; Freiberg. Keywords: Saurichthys, actinopterygian fishes, Triassic freshwater fish faunas, endemism. Addresses: Dipl.-Geol. I. Kogan, K. Schönberger, Dipl.-Geol. J. Fischer & Dr. S. Voigt, TU Bergakademie Freiberg, Geological Institute, Dept. of Palaeontology, Bernhard-von-Cotta street 2, Freiberg, Germany; i.kogan@gmx.de. Contents: Abstract Zusammenfassung 1 Introduction 2 Geological setting 3 Systematic palaeontology 4 Ichthyofaunal assemblage 5 Discussion 6 Conclusions Acknowledgements References Abstract A fish skeleton recently found in lacustrine siltstones of the Madygen Formation (Southwestern Kyrgyzstan, Central Asia; Ladinian Carnian) represents the largest and most complete specimen of Saurichthys orientalis SYTCHEVSKAYA, 1999 known so far. It features six longitudinal rows of scales. The total body length is estimated to be 45 cm. Along with the hybodont shark Lissodus, Saurichthys is a cosmopolitan taxon within an assemblage of apparently endemic actinopterygians and a dipnoan, indicating that the basin had at least temporary drainage to other aquatic systems. The preliminary description of the Saurichthys specimen is followed by a discussion on systematic aspects and on the palaeobiogeography and palaeoecology of the Madygen ichthyofauna. Zusammenfassung Ein kürzlich aus lakustrinen Schluffsteinen der Madygen-Formation (Südwest-Kirgisistan, Zentralasien; Ladin Karn) geborgenes Fischskelett stellt das bislang größte und vollständigste Exemplar von Saurichthys orientalis SYTCHEVSKAYA, 1999 dar. Es besitzt sechs longitudinale Schuppenreihen. Die gesamte Körperlänge wird auf etwa 45 cm geschätzt. Neben dem hybodonten Hai Lissodus ist auch Saurichthys ein kosmopolitischer Vertreter innerhalb einer Assoziation von scheinbar endemischen Actinopterygiern und einem Dipnoer, was auf zumindest temporäre Verbindungen des Beckens zu anderen aquatischen Systemen hinweist. Basierend auf der vorläufigen Beschreibung des Saurichthys-Fundes werden systematische Aspekte sowie Paläobiogeographie und Paläoökologie der Madygen-Ichthyofauna diskutiert. 139

2 I. Kogan et al. / Freiberger Forschungshefte C 532 psf 17 (2009): Introduction For more than 80 years, the type area of the non-marine Triassic Madygen Formation in southwest Kyrgyzstan (Central Asia, Fig. 1) has attracted attention by its exceptional fossil content (KOCHNEV, 1934; DOBRUSKINA, 1995; VOIGT et al., 2006). The number, diversity and preservation of findings classify it as a conservation/concentration lagerstätte (VOIGT et al., 2006; SHCHERBAKOV, 2008). In 2006, VOIGT and colleagues started an integrative study of the Madygen Formation in order to reconstruct the depositional environment, the evolutionary history of the Madygen basin and the palaeoecology of its biota (e.g. VOIGT et al., 2006, 2007, 2009b). The Madygen basin is of special interest because the fluvio-lacustrine deposits belong to one of only few occurrences of continental Triassic beds in Central Asia. Stratigraphically, the Madygen Formation is assumed to represent Middle to Late Triassic age (Ladinian Carnian), based on macrofloral correlations (DOBRUSKINA, 1995). Fig. 1: Simplified political map showing the location of the study area in Central Asia (modified from VOIGT et al., 2006). The stippled rectangle marks the type area of the Madygen Formation (Fig. 2). The fossil record of the Madygen Formation is dominated by plants and insects. It yielded one of the most diverse Early Mesozoic floras of Eurasia (DOBRUSKINA, 1970, 1982, 1995; MOISAN et al., 2008, 2009) and more than insects of almost all Triassic lineages (SHAROV, 1971; RASNITSYN & QUICKE, 2002; SHCHERBAKOV, 2008). Furthermore, the fossil fauna comprises microconchids, molluscs and crustaceans (VOIGT, 2007; VOIGT et al., 2007), freshwater sharks (FISCHER et al., 2007, 2009), actinopterygians (SYCHEVSKAYA, 1999), lungfish (Asiatoceratodus VOROBYEVA, 1967), a larval urodelan (Triassurus IVACHNENKO, 1978), a chroniosuchid (BUCHWITZ & VOIGT, 2009; BUCHWITZ et al., 2009; SCHOCH et al., in press), a small procynosuchid cynodont (Madysaurus TATARINOV, 2005) and two small diapsids with unique soft-tissue preservation (Sharovipteryx COWEN, 1981, and Longisquama SHAROV, 1970; VOIGT et al., 2009a). Among abundant fossil fishes that have been collected since 2006 during several field seasons by the Freiberg working group, remains of Saurichthys orientalis SYTCHEVSKAYA, 1999 are rare and hitherto confined to isolated teeth (Fig. 5A; VOIGT et al., 2007). Here we report on the 2008 discovery of an articulated specimen, which represents the largest and most complete individual of the taxon. Apart from systematic aspects, this paper focuses on palaeoenvironmental and biogeographic implications of Saurichthys and other fishes from the study area. 140

3 A nearly complete skeleton of Saurichthys orientalis from the Madygen Formation (Central Asia). 2 Geological setting The Saurichthys specimen described below has been recovered at the Madygen fossil site situated about 50 km to the west of Batken, the capital of the eponymous administrative district in southwestern Kyrgyzstan, Central Asia (Fig. 1). The Madygen fossil site is the stratotype area of the Madygen Formation, which is represented by an up to 560 m thick succession of complexly interbedded alluvio-fluvial to lacustrine deposits that introduce the Mesozoic Cenozoic platform cover at the northern foothills of the Turkestan Range (VOIGT et al., 2009b). According to preliminary results of our recent studies on the lithostratigraphy (VOIGT in prep.), the Madygen Formation of the type area records three intervals of lacustrine deposits ranging in thickness from about 40 to 190 m. Because of the limited outcrop area it is impossible to infer if the successions of lacustrine deposits represent one single lake with significantly fluctuating shoreline or three independent lakes, which successively evolved. Based on the distribution of referred sediments near the top of the formation, the minimum lateral extent of the lacustrine environment can be estimated to about 1.7 km (Voigt et al., 2007). Remains of Saurichthys orientalis have been found in all three levels of lake deposits (Fig. 2) and comprise partially articulated material (SELEZNEVA & SYTCHEVSKAYA, 1989; SYTCHEVSKAYA, 1999) that most likely comes from lacustrine level 2 of the northwestern outcrop area of the Madygen Formation (Urochishche Dzhaylyaucho), and isolated teeth (VOIGT et al., 2007 and unpublished data) from lacustrine levels 1 and 3 of the southwestern outcrop area (Urochishche Madygen). Fig. 2: Simplified geological map of the study area showing the geographic and stratigraphic position of Saurichthys orientalis remains within the Madygen Formation (modified from VOIGT & HOPPE, in press; basic mapping after DOBRUSKINA, 1970): I Urochishche (= landmark) Madygen; II Urochishche Dzhaylyaucho; a presumed position of the material described by SYTCHEVSKAYA (1999); b position of the isolated tooth FG 596/III/11; c position of the skeleton FG 596/III/43. The nearly complete Saurichthys skeleton focused herein has been excavated from laminated siltstones at about the middle part of the lacustrine level 1 of the southwestern outcrop area of the Madygen Formation (Fig. 2). It was closely associated with plant debris, macrofloral remains, kazacharthran phyllopods and insects (Fig. 3). In particular, abundant plant fragments, a partially articulated tetrapod skeleton and intercalations of wavy-bedded sandstones recorded from the same horizon indicate an increased input of continental debris and a rather marginal position of the Saurichthys locality within the Madygen palaeolake. 141

4 I. Kogan et al. / Freiberger Forschungshefte C 532 psf 17 (2009): Systematic palaeontology Class Osteichthyes HUXLEY, 1880 Subclass Actinopterygii COPE, 1887 Order Saurichthyiformes ALDINGER, 1937 Family Saurichthyidae STENSIÖ, 1925 Genus Saurichthys AGASSIZ, 1834 Type species: Saurichthys apicalis AGASSIZ, 1834 The genus Saurichthys was defined by AGASSIZ (1834) on the basis of a jaw fragment from the upper Muschelkalk (Ladinian) of Bayreuth, Germany. The name lizard fish served to emphasize the similarity of saurichthyid teeth to those of reptiles and AGASSIZ ( ) supposed that these fishes have an intermediate position between normal fishes and reptiles. A great number of subsequent studies (e.g. STENSIÖ, 1925; PIVETEAU, ; GRIFFITH, 1959, 1962, 1977; RIEPPEL, 1980, 1985, 1992; BÜRGIN, 1990, TINTORI, 1990) provided the knowledge on this genus, which now includes nearly 50 species from predominantly marine, but also non-marine deposits of all parts of the world. However, since many of the findings attributed to Saurichthys are only isolated teeth or jaw fragments, doubts persist on identifications and specific diagnoses. As already pointed out by MUTTER et al. (2008), the whole genus needs taxonomic revision. Fig. 3: Detailed stratigraphic section of the find locality of the Saurichthys specimen FG 596/III/43. Saurichthyids are characterised by a long, slender body with an extremely elongated head of around one third of the total body length, sometimes even longer (e.g. GRIFFITH, 1959), tapering forward in a rostrum. The jaws bear a dentition of predatory type, consisting of large conical teeth showing a typical longitudinal striation in alternation with series of smaller teeth. Pelvic, anal and dorsal fins are small and placed relatively far posteriorly with dorsal opposing anal fin (GARDINER, 1960). Squamation is mostly reduced to dermal plates or scales of different shape, arranged in two to six longitudinal lines. Saurichthys is interpreted to have originally been a fastswimming pelagic fish, whereas some younger representatives were adapted to shallow lagoons, reef-near habitats or lacustrine environments (RIEPPEL, 1985, 1992). Saurichthys orientalis SYTCHEVSKAYA, 1999 Material: FG 596/III/43 (Fig. 4A), articulated skeleton without tail and snout tip, preserved in lateral view on disintegrated fragments of rock, mainly with counterpart. Description: The preserved portion of the specimen (Fig. 4A, B) is approximately 33.5 cm long. It extends from the snout to the region of the dorsal and anal fins. The body is bent slightly in dorsoventral direction and displays a pattern of torsion increasing cranially (Fig. 4C). The skull itself is preserved in lateral view but with some rotation of the lower jaw, so that the tooth-bearing dorsal margin of the right dentary lies under sediment cover under the teeth of the right maxilla and the ventral margin of the left dentary is exposed. 142

5 A nearly complete skeleton of Saurichthys orientalis from the Madygen Formation (Central Asia). The skull measures 11.1 cm including the opercle. It is dominated by the elongated snout composed of the premaxilla and the dentary. The premaxilla bears delicate posteroventrally running striae. The dentaries are ornamented with delicate striae running anteroventrally, longitudinal ridges on the ventral margin and tubercles on the posterior end. Teeth could be observed on the premaxilla, ranging from 0.6 mm to 2.6 mm in height. All teeth are conical and show a more or less delicate longitudinal striation of their basal part. The premaxilla contacts posteriorly the nasalo-antorbital and the maxilla, the latter extending behind the orbit. The posterior part of the lower jaw is formed by the angular that is triangular in shape and extends probably to the posterior margin of the orbit (as can be supposed from the counterpart). No further bones or sutures of the skull can be described at present due to the preservation and the position in the embedding sediment. The opercle is of nearly triangular shape and almost as long as deep (1.0 to 1.2 cm approx.). It is ornamented by short ridges and tubercles. The cleithrum is T-shaped and partly covered by the opercle, which might be an effect of displacement. The left pectoral fin is rounded and has about 26 unsegmented fin rays, the longest of them measuring about 1.2 cm. The right pectoral fin is shifted dorsally and badly preserved. Between the fins, a longitudinal field of oblique bony plates is exposed that is interpreted as the postpectoral field of irregular plates referred to by SYTCHEVSKAYA (1999). The pelvic fins are incompletely preserved. The left pelvic fin consists of at least 23 fin rays. The opposing anal and dorsal fins are incompletely preserved as well. The dorsal fin features at least 31 fin rays, the posteriormost of them being very small. Most of the fin rays are segmented twice. The anal fin shows one segmentation at least. The squamation consists of six rows of scales: one row of mid-dorsal and of mid-ventral ridge scales, and paired rows of mid-lateral and ventro-lateral scales. The ridge scales are rhombic to oval and longer than broad. The ventral scale row is bifurcated in a 1.6 cm long section starting about the middle of the pelvic fin. The scales decrease in size anteriorly and cannot be traced until the pectoral fin. The ventro-lateral scales, developed at least between the pectoral and the pelvic fins, are rectangular to rhombic, mostly with one elongated edge. The midlateral scales are triangular to arc- or bow-shaped, with elongate ventral and dorsal branches in the anterior part of the body. The triangles point caudally, and the posterior edge of each overlaps the anterior margin of the following. The mid-lateral scales are inclined, their dorsal branch pointing cranially. Few can be reported at the moment on the ornamentation of the scales, as most of them are preserved in medial view, i.e. displaying the inner side. As far as can be observed, they are ornamented with tubercles. Single ganoid tubercles found in the sediment and not attributable to any of these scale rows imply the possible presence of further scales on some places of the body. The vertebral column consists of ossified neural and haemal arches, best observable behind the pelvic fins. No anatomical details of the haemal arches can at present be described. The neural arches are very prominent, having small praezygapophyses and distinct neural spines, increasing in size posteriorly. Two neural arches seem to correspond to one lateral scale. Remarks: Saurichthys orientalis, described by SYTCHEVSKAYA (1999) on the basis of fragmentary material from the Madygen Formation, was defined by a particular structure of the parietal complex, the opercle strongly convex posteriorly, somewhat elongated pectoral fins and the presence of a post-pectoral field of bony plates. Though no evidence is found on specimen FG 596/III/43 for elongated pectoral fins, the other features observable on the specimen seem to allow its attribution to this taxon. The missing part of the snout might be equal to its anteriormost quarter. Together with a typical saurichthyid tail, the total body length can be estimated to about 45 cm (Fig. 4D). This is twice larger than estimated by SYTCHEVSKAYA (1999), who assumed a body length of no more than 20 cm. Nevertheless, S. orientalis has to be regarded as a small representative (see discussion). Whereas first remains attributed to Saurichthys are reported from latest Permian (MUTTER et al., 2008; MINIKH et al., 2009), its radiation is nearly global by the beginning of the Triassic (e.g. BELTAN & TINTORI, 1981; MUTTER et al., 2008). JIN (2006) proposes the uppermost Permian Eosaurichthys chaoi from southern China as the possible ancestor. Although several authors (e.g. BELTAN & JANVIER, 1978; BELTAN & TINTORI, 1981; MUTTER et al., 2008) state that the evolution of Saurichthys was not orthogenetic, RIEPPEL (1992) was able to present a cladogram of some Saurichthys species illustrating the most important phylogenetic trends. Within the general trend of reducing ossification, he listed the decreasing number of the dermal skull bones, the reduction of the squamation and the number of fin-rays and possibly their decreasing segmentation. Further changes of probably phylogenetic value concern the anatomy of the vertebral column (e.g. TINTORI, 1990; RIEPPEL, 1992; WU et al., 2009). 143

6 I. Kogan et al. / Freiberger Forschungshefte C 532 psf 17 (2009):

7 A nearly complete skeleton of Saurichthys orientalis from the Madygen Formation (Central Asia). 4 Associated ichthyofauna Fossil fishes of the Madygen Formation have been studied by VOROBYEVA (1967), SELEZNEVA & SYTCHEVSKAYA (1989) and, most recently, by SYTCHEVSKAYA (1999). Furthermore, they were part of a PhD thesis by YAKOVLEV, which has not been available to us. His results, however, were re-examined and partly revised by SYTCHEVSKAYA (1999). In the course of the resumption of fieldwork in the stratotype area of the Madygen Formation by VOIGT and colleagues, in the last few years supplementary material of articulated fish skeletons, partial remains, isolated dermal bones, scales, teeth and coprolites was collected, extending the knowledge of already reported taxa and providing evidence of others (e.g. VOIGT et al., 2006, 2007; FISCHER et al., 2007). The fish assemblage of the study area is dominated by ganoid-scaled actinopterygians comprising at least six genera of four families (SYTCHEVSKAYA, 1999). Apart from (1) the above described Saurichthys orientalis, these are: the by far most abundant small to medium-sized (10 to 20 cm) palaeoniscids (2) Sixtelia asiatica SYTCHEVSKAYA, 1999 (Fig. 5B) and (3) Ferganiscus osteolepis SYTCHEVSKAYA & YAKOVLEV, 1999 (Fig. 5C); the also small to medium-sized perleidids (4) Alvinia serrata SYTCHEVSKAYA, 1999 and (5) Megaperleidus lissolepis SYTCHEVSKAYA, 1999; and (6) the evenkiid Oshia ferganica SYTCHEVSKAYA, 1999 (Fig. 5D). Based on their rather weak teeth, we tend to interpret the Madygen palaeoniscids and perleidids as pelagic planktivorous to insectivorous fishes; Oshia ferganica is an up to 45 cm large form with a typical predatory dentition (tusk-shaped teeth alternating with series of smaller teeth; SYTCHEVSKAYA, 1999). Exceptionally complete and well preserved dipnoan remains allowed VOROBYEVA (1967) to describe the taxon Asiatoceratodus sharovi (Fig. 5H). This rather small (up to 30 cm) lungfish lived near the lake shoreline and fed on benthic organisms. At least two definite taxa of elasmobranches are documented by two distinct types of egg capsules (Palaeoxyris BRONGNIART, 1828, and an indeterminate type; Fig. 5E, F) found and described by FISCHER et al. (2007), and isolated hybodont teeth (Fig. 5G; FISCHER et al., 2009; FISCHER et al. in prep.). Those teeth are assigned to the small, durophagous shark Lissodus BROUGH, 1935, which is also believed to be the producer of the Madygen Palaeoxyris capsules (FISCHER & KOGAN, 2008; FISCHER et al., 2009); the other elasmobranch is not yet determined. Both apparently preferred the vegetated shallow water zones along lake shorelines and discharging streams as specific freshwater nesting grounds. 5 Discussion The study of the Saurichthys remains in their ichthyofaunal context bears a potential of new insights into the ecology, the palaeobiogeographic, and the stratigraphic position of the lacustrine ecosystem. Here we discuss some preliminary results of the ongoing work. 5.1 Affinities of Saurichthys orientalis The preservation and position of the specimen does not allow a detailed comparison with other Saurichthys species at the moment. Some details of the skull morphology and the structure of the vertebral column will be recovered by further preparation of the specimen. As far as can be judged now, the neural arches bearing neural spines and distinct but relatively small praezygapophyses resemble those figured by RIEPPEL (1985) for the Anisian Ladinian S. curionii and S. costasquamosus as well as those of the Anisian S. dawaziensis (WU et al., 2009). The convex shape of the opercle resembles several Early Triassic forms, especially S. elongatus and S. wimani from Spitzbergen (STENSIÖ, 1925), S. madagascariensis from Madagascar (PIVETEAU, ; LEHMAN, 1952; RIEPPEL, 1980), but also S. toxolepis from British Columbia (MUTTER et al., 2008). One of the most striking features of S. orientalis is the unusual squamation pattern. Whereas some Early Triassic saurichthyids have a complete squamation (RIEPPEL, 1980), four to two rows of scales are typical for the majority of species (STENSIÖ, 1925; GARDINER, 1960). In having six distinct rows of scales, S. orientalis resembles the Middle Triassic (Anisian Ladinian) species of Monte San Giorgio, Switzerland (S. macrocephalus, S. curionii, S. costasquamosus, S. paucitrichus and possible further species not described yet [RIEPPEL, 1985, 1992]), and especially S. toxolepis from the Early Triassic of British Columbia (MUTTER et al., 2008). This latter species shares with S. orientalis not only the arrangement of scale rows, but also the shape of the scales. 145

8 I. Kogan et al. / Freiberger Forschungshefte C 532 psf 17 (2009): Fig. 5: Ichthyofaunal remains from the Madygen Formation. A tooth of Saurichthys orientalis SYTCHEVSKAYA, 1999 (FG 596/III/11); B Sixtelia asiatica SYTCHEVSKAYA, 1999 (FG 596/III/3); C Ferganiscus osteolepis SYTCHEVSKAYA & YAKOVLEV, 1999 (FG 596/III/9); D scales tentatively assigned to Oshia ferganica SYTCHEVSKAYA, 1999 (FG 596/III/44); E elasmobranch egg capsule of undetermined type (FG 596/III/2); F Palaeoxyris sp. (FG 596/III/13); G tooth of Lissodus sp. (FG 596/III/42); H Asiatoceratodus sharovi VOROBYEVA, 1967 (FG 596/III/45). 146

9 A nearly complete skeleton of Saurichthys orientalis from the Madygen Formation (Central Asia). 5.2 Fish body size and mode of preservation Many fish skeletons from the Madygen Formation including the Saurichthys specimen described herein are articulated, suggesting parautochthonous to autochthonous preservation under low-energy conditions of the Madygen palaeolake environment. The mode of preservation of fish skeletons depends on various factors like water temperature, water depth, distance of transportation and sedimentation rate (ELDER & SMITH, 1988; MANCUSO, 2003; ZOHAR et al., 2008). Most favourable are deep, stratified lakes with anoxic bottom water where no destruction of organic matter occurs; however, the absence of black shales or varvae typical for this environment as well as the abundance of invertebrate traces in lacustrine deposits of the Madygen Formation (VOIGT et al., 2006; VOIGT & HOPPE, in press) suggests that the lake bottom was oxygenated. Furthermore, the wavy-bedded sandstones intercalated with the fossiliferous siltstones in the section where the Saurichthys skeleton was recovered indicate a rather near shore position in the lake. The articulated but deformed preservation of the specimen suggests that the body was filled with bubbles of decay gas before compaction. However, it did probably not float on the water surface, as the body is only slightly bent along its axis and no parts are primarily missing, as one could expect in case of flotation (ELDER & SMITH, 1988). We therefore suppose that the fish sunk to the bottom and remained under a sufficient water pressure until it was covered by sediment. The fact that it was not destructed by scavengers could be explained by unfavourable conditions (e.g. low oxygen level, salinity) or a rapid embedding. The torsion of the body might be an effect of a sediment current. The small size of most of the Madygen fishes is a further noticeable fact. Although Saurichthys species reported from freshwater deposits hardly exceed 1 m in body length (e.g. CHOU & LIU, 1957; TURNER, 1982; WADE, 1935) a body size smaller than 50 cm is rather an exception. SYTCHEVSKAYA (1999) had even to assume a body length of no more than 20 cm on the basis of the specimens available to her. As concerns other actinopterygians, the dominance of individuals no bigger than 10 cm is noteworthy. The lungfish Asiatoceratodus sharovi, with its at present known maximum length of 30 cm, is also a small form compared to other coeval ceratodontoids reaching 1 m and more in length (VOROBYEVA, 1967). Two potential causes are proposed to explain this phenomenon: (1) the taphocoenosis could be dominated by juvenile individuals (e.g. for some fossil [SCHNEIDER, 1996; PIMIENTO et al., 2009] and recent [COMPAGNO, 1990; CASTRO, 1993; HEUPEL et al., 2007] sharks a habitat selection behaviour for the young is noted that helps them to avoid conspecific predators); or (2) the most fishes could only have reached a reduced body size as a result of ecologic stress. Mass mortality of young fishes can also be caused by periodical toxic events like seasonal turnover of lakes (ELDER & SMITH, 1988). 5.3 Palaeobiogeographic implications According to SYTCHEVSKAYA (1999), the genera Sixtelia, Ferganiscus, Alvinia, Megaperleidus and Oshia are endemic for the Madygen Formation. The assumption of a possible isolated development of the Madygen habitat seems supported by the apparently unique assemblage of tetrapods (SHAROV, 1970, 1971; IVAKHNENKO, 1978; TATARINOV, 1994, 2005; SCHOCH et al., in press). An evenkiid and perleidids similar to Megaperleidus are, however, found in Early Triassic deposits of the Tunguska River basin in Siberia (SYTCHEVSKAYA, 1999), and further relatives of all hitherto known Madygen fish groups (palaeoniscids, perleidids, saurichthyids,?scanilepiforms, ceratodontoids, hybodonts) are known from freshwater deposits of northern China (CHANG & MIAO, 2004; JIN, 2006). The latter do not co-occur together in the same strata but are stratigraphically distributed over the entire Triassic. Nevertheless, the existence of a huge faunal province comprising central and northern Asia (SYTCHEVSKAYA, 1999) or central Asia and northern China (CHANG & MIAO, 2004) at least in the Early Triassic is proposed by the authors. Furthermore, the apparent endemism of the Madygen taxa might to some degree be artificial, representing the effect of sampling or preservation bias of Triassic freshwater fishes (SYTCHEVSKAYA, 1999; VOIGT et al., 2006). The only Madygen fish genera that are reported from other localities are: Saurichthys, Asiatoceratodus and Lissodus. However, only Saurichthys and Lissodus can be considered as true cosmopolitans. The systematics of post-palaeozoic lungfishes is problematic, because skeletal remains are rare and many taxa are based on isolated tooth plates only; in addition, the high variation of skull morphologies complicates establishing phylogenetic relationships (e.g. VOROBYEVA, 1967; KEMP, 1998; CAVIN et al., 2007). Whereas VOROBYEVA s (1967) Asiatoceratodus sharovi is based on exceptionally complete and well-preserved material (tooth plates, cranial bones, body scales, vertebral column etc.), other specimens referred to Asiatoceratodus from North America, Europe and Africa (SCHULTZE, 1992; KEMP, 1998; GOODWIN et al., 1999) are only fragmentary. We thus agree with CAVIN et al. (2007) who doubt on further identifications of Asiatoceratodus, and prefer to deal with ceratodontoid lungfishes for needs of comparison. There is no consensus on the ecologic significance of lungfishes. Whereas JAIN (1986) believes them to indicate warm and freshwater conditions (recent lungfishes 147

10 I. Kogan et al. / Freiberger Forschungshefte C 532 psf 17 (2009): having a water temperature preference of 25 C, although it may range from 11 C to 31 C), SCHULTZE (2004) states that the occurrence of dipnoans in marine deposits can only be explained by a high saltwater tolerance. Both Saurichthys and Lissodus, in contrast, are genera that show a global distribution in marine and freshwater strata (e.g. MUTTER et al. 2008; FISCHER, 2008). Fragmentary Saurichthys remains have been reported from various Early and Middle Triassic sections of the former Soviet Union (mostly European, but also Asian part of Russia; MINIKH, 1981, 1982, 1992; MINIKH & MINIKH, 2006). Marine Early Triassic (Olenekian) strata of Mangyshlak, Western Kazakhstan, represent the occurrence nearest to Madygen (MINIKH, 1981). Probable freshwater deposits of Qilingou, Hengshan in northern China yielded S. huanshenensis, described by CHOU & LIU (1957). Originally interpreted as Early Triassic, they are now dated as Rhaetian (JIN, 2006). Further Saurichthys remains, some of which are yet to be described as new species, are found in marine Early Middle Triassic (Induan Ladinian) deposits of southern China (JIN, 2006). Most recently, WU et al. (2009) introduced the new species S. dawaziensis from the Anisian of Luoping, Yunnan Province. Skeletal remains as well as indirect evidences (i.e. Palaeoxyris egg capsules) of hybodonts, especially Lissodus- Lonchidion-like sharks are rare in Central Asia (FISCHER, 2008). There is one report of Hybodus youngi from late Ladinian freshwater deposits of northern China (LIU, 1962; JIN, 2006), and a poorly described remain of Spirangium [Palaeoxyris] gilewi from Late Triassic of Kazakhstan (ROMANOWSKI, 1880). Otherwise, egg capsules from Madygen are similar to P. regularis from the Anisian of the northern Vosges, France, and P. muensteri from the Late Triassic of Germany (FISCHER et al., 2007). Undoubted freshwater occurrences of Lissodus respectively Lonchidion are reported from the Early Middle Triassic (Scythian Anisian) of South Africa (e.g. BROOM, 1909; BROUGH, 1935; BENDER & HANCOX, 2004), the Late Triassic (Carnian Rhaetian) of northern America (e.g. MURRY, 1981; HECKERT, 2004; MILNER et al., 2006), and the Late Triassic (Carnian Norian) of India (PRASAD et al., 2008; PRASAD & SINGH, 2009). The occurrence of the cosmopolitan taxa Saurichthys and Lissodus in the Madygen Formation indicates drainage to other basins or even directly to the Palaeo-Tethys. In latter case it could point to potential diadromous behaviour of both taxa. Their wide palaeogeographical occurrence indicates a faunal exchange during the existence of the Madygen ecosystem clearly contradicting an internally drained intramontane basin model (see complete overview in VOIGT et al., 2006). 6 Conclusions Saurichthys orientalis is a small saurichthyid with an unusual squamation consisting of six rows of scales, segmented unpaired fins, an opercle strongly convex posteriorly and neural arches bearing small but distinct praezygapophyses. It especially resembles Saurichthys toxolepis from Olenekian of British Columbia. Along with the hybodont shark Lissodus, Saurichthys represents the only cosmopolitan form in an assemblage dominated by apparently endemic actinopterygians and comprising furthermore a ceratodontoid lungfish. The occurrence of these cosmopolitan forms suggests the existence of drainage systems to other freshwater basins or even to the Palaeo-Tethys. Comparable ichthyofaunal assemblages are known from several Early and Middle Triassic localities in northern and southern hemisphere (e.g. southern Cis-Ural, MINIKH, 1992; MINIKH & MINIKH, 2006 or Karoo Basin in South Africa, BENDER & HANCOX, 2003, 2004). The Madygen taphocoenosis is dominated by articulated remains of small fishes that could either be juvenile individuals or adult forms with a reduced body size. The conditions that allowed this preservation comprised a sufficient water depth, maybe a moderate water temperature and probably a considerable sedimentation rate. Acknowledgements The specimen was found during the 2008 field season by KATHARINA SCHÖNBERGER, ANDREAS BROSIG, JULIANE HENTSCHKE (all Freiberg) and PHILIPPE MOISAN (Münster). The manuscript has been kindly revised by Prof. Dr. ANDREA TINTORI (Milano) and Dr. WU FEIXIANG (Beijing). We wish to express our thank to Dr. EVGENIA K. SYTCHEVSKAYA (Moscow), Dr. SUSAN TURNER (Queensland), Dr. ADRIANA LÓPEZ-ARBARELLO (Munich), Dr. RALF WERNEBURG (Schleusingen) and CATALINA PIMIENTO (Gainesville) who greatly supported our work by providing literature and additional information, and to Prof. Dr. JÖRG W. SCHNEIDER and Dr. OLAF ELICKI (both Freiberg) for discussions. Many thanks are due to Dr. LEE W. JANSON (Edinburgh) and MICHAEL BUCHWITZ (Freiberg) for their linguistic and professional remarks that helped improving the manuscript. Dr. MICHAEL MAGNUS (Freiberg) friendly helped in taking microscopic photographs. The drawings of the skeleton were made by FREDERIK SPINDLER (Freiberg) under the supervision by the leading author. We are thankful to the German Research Foundation (DFG) who supports the research with the grants DFG-VO 1466/1 and DFG- SCHN 408/

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