A new scanilepiform from the Lower Triassic of northern Gansu Province, China, and phylogenetic relationships of non-teleostean Actinopterygii

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1 Zoological Journal of the Linnean Society, 2011, 161, With 7 figures A new scanilepiform from the Lower Triassic of northern Gansu Province, China, and phylogenetic relationships of non-teleostean Actinopterygii GUANG-HUI XU 1,2 and KE-QIN GAO 1 * 1 School of Earth and Space Sciences, Peking University, Beijing, , China 2 Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, , China Received 28 August 2009; revised 2 November 2009; accepted for publication 12 November 2009 A new scanilepiform, Beishanichthys brevicaudalis gen. et sp. nov., is named and described based on fossils from the Lower Triassic lake deposits exposed in Beishan area, Gansu Province, China. The discovery documents a new record of this group, which is significantly older than other known scanilepiforms from China, and is slightly younger than Evenkia from the Lowest Triassic of Central Siberia. Although the Beishan beds were previously interpreted as Late Permian in age, based on megaplant fossils, this new discovery supports the reinterpretation of the deposits as Early Triassic in age, based on vertebrate fossils from the same locality and horizon. Phylogenetic analysis was conducted to resolve the relationships of Scanilepiformes with other actinopterygian clades, and the inter-relationships within Scanilepiformes. Contrary to previous thought that scanilepiforms are closely related to the Amiidae, the phylogenetic results of this study recognize the Scanilepiformes as stem-group neopterygians. Relationships of the Scanilepiformes and Australosomus with other neopterygians remain unresolved. With a characteristic long-based dorsal fin, scanilepiforms represent a small group that emerged in Early Triassic freshwater environments, inhabited Eurasia and North America during the Middle Late Triassic, briefly invaded the marine environment by the Late Triassic in Europe, and became extinct at the end of Triassic.. doi: /j x ADDITIONAL KEYWORDS: Neopterygii osteology phylogeny Triassic fish. INTRODUCTION The Actinopterygii, or ray-finned fishes, are the most diverse group of living vertebrates, including approximate extant species (Nelson, 2006). The earliest definitive record of actinopterygians with articulated remains comes from the Middle Devonian, but Devonian actinopterygians are still relatively uncommon, with 13 genera described based on articulated material (Long, Choo & Young, 2008; Choo, Long & Trinajstic, 2009). A much greater diversification of actinopterygians occurred in the Carboniferous and Permian, with approximate 80 genera known *Corresponding author. kqgao@pku.edu.cn from those periods (Gardiner, 1993). In the Triassic, the advanced actinopterygians, neopterygians, became dominant both in diversity and individual abundance, whereas the lower actinopterygians, the so-called palaeoniscoids, survived till the end of the Cretaceous. The Scanilepiformes Sytchevskaya, 1999 are an extinct group of palaeoniscoid fishes with a geological range confined to the Triassic. The first scanilepiform was named and assigned to the ganoid genus Gyrolepis (Gyrolepis dubius) based on incomplete material from the Rhaetian marine deposits of Scania, Sweden (Woodward, 1893). This species was later reassigned to the genus Scanilepis in its own family Scanilepididae under the Palaeonisciformes (Aldinger, 1937). 595

2 596 G.-H. XU and K.-Q. GAO Lehman (1979: 113) redescribed Scanilepis dubius, and suggested that it was probably to be placed near the origin of the Amiidae. More recently, Gardiner & Schaeffer (1989) placed Scanilepis in the probably paraphyletic Palaeoniscum group for its great number of irregular supraorbitals between the nasals and dermosphenotics (but see phylogenetic discussion below). Berg (1941) described the second scanilepiform genus Evenkia based on the material from the Lowest Triassic of Tunguska River Basin, Central Siberia. The same author classified the genus in the family Palaeoniscidae, although noted its close similarity with Scanilepis in having a long-based dorsal fin. Selezneva (1985) later erected a monotypic family Evenkiidae and placed it in the order Cheirolepiformes, but this placement is problematic because Evenkia lacks diagnostic features shared by known cheirolepiforms from Devonian deposits. Sytchevskaya (1999) agreed with Berg (1941) that Evenkia was a close relative of Scanilepis, and named the order Scanilepiformes to include the Evenkiidae and Scanilepididae. In the same publication, Sytchevskaya (1999) also named the evenkiid genus Oshia based on incomplete material from the Middle Triassic of the Fergana Depression of Kirghizstan. Schaeffer (1967) named another possible scanilepiform, Tanaocrossus kalliokoskii, based on an incomplete specimen from the Upper Triassic Chinle Formation of Colorado, and placed the genus and species in the Palaeonisciformes without reference to a particular family. A second specimen of the same genus and species is known from an incomplete anal fin from the Triassic part of the Newark Supergroup, Virginia (Schaeffer & Donald, 1978). The genus Tanaocrossus was placed in the Scanilepididae by Gardiner (1993). More recently, Milner, Spears & Olsen (2008) found new Tanaocrossus material with skulls preserved from the Owl Rock Member of the Chinle Formation in San Juan County, Utah, and the lower part of the Bull Canyon Formation in Quay County, New Mexico, and based on their study of the new material, Milner et al. (2008) reassigned Tanaocrossus to the Perleidiformes (but see comparison and phylogenetic discussion below). In China, two previously known scanilepiforms are: Fukangichthys longidorsalis Su, 1978, from the Middle Triassic Kelamayi Formation of Xinjiang (Lucas & Johnson, 2002), and Mizhilepis zhangyaensis Liu & Shen, 2006, from the Upper Triassic Wuyaobu (Wayaopu) Formation, Mizhi County, northern Shaanxi Province. Both taxa were inadequately described, and a revision of these problematic taxa is beyond the scope of this paper. This paper reports the discovery of a new scanilepiform from the Lower Triassic deposits of the Figure 1. Map showing the type locality of Beishanichthys brevicaudalis gen. et sp. nov. in northern Gansu Province, China. Hongyanjing Formation, exposed in Beishan Hills, northern Gansu Province, China (Fig. 1). The new taxon under study is known from six well-preserved specimens from the same locality and horizon. Along with these is a rich vertebrate fauna represented by thousands of other fish specimens, hundreds of temnospondyl and lepospondyl amphibians, a few lizardlike diapsid reptiles, and a trirachodontid eucynodont (Gao et al., 2004; Xu & Gao, 2007, 2008). The fossilbearing deposits of dark mudstones and siltstones exposed at the Beishan site were previously interpreted as Late Permian in age, based on problematic plant fossils (Yang, Fan & Yao, 1997), but have been revised as Early Triassic (Olenekian), based on vertebrate fossils, and primarily on the trirachodontid eucynodont (Gao et al., 2008; 2010). Therefore, the new scanilepiform from the Beishan site is slightly younger than Evenkia from the Lowest Triassic of the Tunguska River Basin, Central Siberia (Sytchevskaya, 1999), but is significantly older than the other scanilepiforms mentioned above. This new discovery stimulated a phylogenetic analysis to resolve the relationships of the Scanilepiformes as a significant but poorly known group of early actinopterygians. MATERIAL AND METHODS The specimens of the new taxon are reposited in Peking University Paleontological Collections (PKUP). All the specimens are laterally compressed, and have been split into part and counterpart slabs. The specimens were prepared manually, and latex peels were made for observation of anatomical details. The fossil specimens and latex peels were dusted with ammonium chloride (NH 4Cl) for photography, or photographed with the fossil submerged in clear water

3 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 597 for better contrast. Illustrations were drawn under a Leica MZ8 microscope with the assistance of a camera lucida, and then prepared using Adobe Photoshop and Illustrator (vcs4). Cladistic analysis was executed using PAUP 4.0b10 (Swofford, 2003). All measurements of the specimens are given in mm. TERMINOLOGY This paper adopts the broadly applied traditional actinopterygian nomenclature following Gardiner (1984), and Gardiner & Schaeffer (1989). The relative position of the fins and the scale count are expressed in a squamation formula following Westoll (1944), in which the letters D, P, A, and C are followed by a particular numerical value to denote the number of scale rows between the first complete row behind the pectoral girdle and the insertion of the dorsal (D), pelvic (P), anal (A), and caudal (C) fins, respectively. The letter T denotes the total number of scale rows between the pectoral girdle and the caudal inversion. ABBREVIATIONS ANATOMICAL An, angular; Br, branchiostegal rays; Clm, Cleithrum; Den, dentary; Dpt, dermopterotic; Dsp, dermosphenotic; ethc, ethmoid commissal sensory canal; Es, extrascapular; Fr, frontal; ifc, infraorbital sensory canal; Ju, jugal; Lac, lachrymal; Lg, lateralgular; mc, mandibular sensory canal; Gl, lateral gular; Mx, maxilla; Na, nasal; ana, anterior nostril; pna, posterior nostril; Op, opercular; Pa, parietal; Pas, parasphenoid; Pcl, postcleithrum; Pmx, premaxilla; Pop, preopercular; Pt, post-temporal; Quj, quadratojugal; Ro, rostral; Sbo, suborbital; stc, supratemporal commissural sensory canal; Scl, supraclethrium; soc, supraorbital sensory canal; Sop, subopercular; Spo, supraorbital. MEASUREMENTS AFBL, anal fin base length; BD, body depth; CPD, caudal peduncle depth; DFBL, dorsal fin base length; HD, head depth; HL, head length; PAL, preanal length; PDL, predorsal length; PPL, prepectoral length; PVL, prepelvic length; SL, standard length; TL, total length. SYSTEMATIC PALAEONTOLOGY SUBCLASS ACTINOPTERYGII WOODWARD, 1891 INFRACLASS ACTINOPTERI COPE, 1871 SUPERDIVISION NEOPTERYGII REGAN, 1923 ORDER SCANILEPIFORMES SYTCHEVSKAYA, 1999 Emended diagnosis: A stem group of Neopterygii differing from other closely related neopterygians in having: long-based dorsal fin consisting of more than 50 fin rays; lobe-shaped posterior margin of dorsal fin; lobe-shaped posterior margin of anal fin; unforked caudal fin (unknown for Scanilepis); and longitudinal striated ornament on short segments of median fin rays. Constituent taxa: Scanilepis, Evenkia, Oshia, Fukangichthys, Tanaocrossus, Mizhilepis, and the new taxon described herein. Known distribution: Upper Triassic, Sweden; Lower Triassic, Central Siberia; Middle Triassic, Kirghizstan; Middle Upper Triassic, North America; and Lower Middle Triassic, China. Remarks: The diagnostic features of the Scanilepiformes given by Sytchevskaya (1999) are listed as follows: (1) body elongate; (2) dermopterotics tending to fuse with parietal bones; (3) dorsal fin long, extending over most of the back length; (4) pectoral fin with fleshy scaly lobe; (5) caudal fin hemi-heterocercal; (6) fin rays drawn together at the bases, with short segments, longitudinally striated; (7) scales large and smooth; (8) anterior scales may bear striated ornaments. Among the above features: (1) is a plesiomorphic condition widely distributed in actinopterygians; (2) is autapomorphic for Evenkia among scanilepiforms; (3) and (6) are diagnostic states of this group; (4) is also autapomorphic for Evenkia; (5), (7), and (8) are character states commonly seen in many stem neopterygians as plesiomorphic conditions. Thus, the diagnosis of this group is revised in this paper. FAMILY INCERTAE SEDIS GENUS BEISHANICHTHYS GEN. NOV. Type species: Beishanichthys brevicaudalis sp. nov. Diagnosis: As for the type and only known species. Etymology: Beishan refers to the type locality in the Beishan Hills; -ichthys, fish. SPECIES BEISHANICHTHYS BREVICAUDALIS SP. NOV. (FIGS 2 6) Holotype: PKUP V4881, a laterally compressed specimen split into part and counterpart slabs, with pectoral fins missing. Referred specimens: PKUP V , all topotypic specimens exposed in part and counter-part slabs.

4 598 G.-H. XU and K.-Q. GAO Figure 2. Holotype of Beishanichthys brevicaudalis gen. et sp. nov. (PKUP V4881). Specimen in left lateral view. See text for definition of abbreviations. Scale bar: 10 mm. Type locality and horizon: Quarry 3 in the Beishan Hills, Subei County, Gansu Province, northern China; Lower Triassic Hongyanjing Formation. Diagnosis: A scanilepiform differing from other members of the group by having three supraorbitals, two suborbitals, ten pectoral fin rays, 65 dorsal fin rays (most fin rays branched), 24 anal fin rays, 18 caudal fin rays, and a squamation formula of D13/P11,A22,C39/T42. Etymology: Species epithet derived from brevi plus caudalis (Latin for short tail), referring to the short caudal peduncle. DESCRIPTION GENERAL MORPHOLOGY Similar to other scanilepiforms, B. brevicaudalis gen. et sp. nov. has a fusiform body outline, a long-based dorsal fin, and a slightly convex caudal fin (Figs 2 5). The largest specimen (PKUP V4886) reaches a total length of 700 mm. The measurements of three nearly complete specimens are shown in Table 1. SNOUT The rostral is about one-third of the length of the frontal, with a curved anterodorsal margin (Fig. 3). This bone is located anterior to the frontal and anteromedial to the nasal, showing a condition different from crown-group neopterygians that have a reduced rostral not contacting the frontal. The nasal is a deep, slightly curved bone, forming the anterior border of the orbit (Fig. 3). It contacts the premaxilla ventrally, and the frontal and supraorbitals posterodorsally. The anteromedial and posterolateral margins of the nasal are notched for the anterior and posterior nares, respectively. Although the sensory pores on the surface of the nasal are difficult

5 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 599 Figure 3. Beishanichthys brevicaudalis gen. et sp. nov. (PKUP V4885). Specimen in right lateral view. A, photograph of whole specimen. B, cranial skeleton and pectoral girdle (photographed under water), illustrating teeth and sensory canal in premaxilla. C, close-up of cranial skeleton and pectoral girdle. D, line drawing of cranial skeleton and pectoral girdle. See text for definition of abbreviations. Scale bar: 5 mm. to identify, the underlying sensory canal is clearly shown, as that bone was highly compressed during fossilization. The supraorbital sensory canal runs longitudinally through the nasal, and terminates at the posterior part of the frontal. The small premaxilla is located anterior to the maxilla, and bears four conical teeth (Fig. 3). A portion of the ethmoid commissal sensory canal is clearly preserved in this bone, as in other scanilepiforms. Considering this character state, the new taxon Beishanichthys is different from perleidiforms and crown-group neopterygians that have a premaxilla lacking the sensory canal. Phylogenetic analysis indicates that the loss of the sensory canal in the premaxilla is a derived condition for Perleidiformes + crown-group neopterygians. The frontal is the longest bone of the skull roof, and is more than twice the length of the rectangularshaped parietal (Figs 2, 3). The frontal is slightly wider posteriorly than anteriorly, and contacts the parietal along a transverse suture. The dermopterotic (= intertemporal plus supratemporal in more primitive actinopterygians; Gardiner & Schaeffer, 1989) is elongate, flanking the parietal and the posterior part of the frontal. The supratemporal sensory canal runs longitudinally through this bone. The extrascapular series consists of a trapezoidal lateral extrascapular and a subtriangular median extrascapular (Fig. 3). The supratemporal canal enters the lateral extrascapular from the dermopterotic, and has a branch extended to enter the median extrascapular, becoming the supratemporal commissural canal. SKULL ROOF PALATE Because of taphonomic compression, the palatal elements can only be observed through the orbit (Fig. 3). The parasphenoid runs through the orbit, and has an

6 600 G.-H. XU and K.-Q. GAO Figure 4. Beishanichthys brevicaudalis gen. et sp. nov. A, C, PKUP V4883. B, holotype (PKUP V4881, counterpart slab). Specimens in right lateral view. See text for definition of abbreviations. Scale bar: 5 mm. elongate orbital portion. The pterygoid bones are difficult to identify because of poor preservation. INFRAORBITAL AND SUPRAORBITAL BONES The infraorbital bone series includes two elements (a lachrymal and a jugal), in contrast to the four or more elements commonly seen in crown-group neopterygians. An increase in the number of infraorbital elements to three or more has been recognized as a derived condition in actinopterygian evolution (Gardiner & Schaeffer, 1989). The lachrymal is an elongated bone, extending between the premaxilla and the jugal to form the ventral border of the orbit. The jugal is slightly wider than the lachrymal, and forms the posterior border of the orbit. The infraorbital sensory canal runs through the jugal, and branches into four short canals that terminate in the posterior portion of the jugal (Fig. 4). The dermosphenotic seems to be trapezoidal in shape, forming the posterodorsal border of the orbit. Three small rectangular supraorbital bones are located along the lateral margin of the frontal, preventing the nasal from contacting the dermosphenotic above the orbit (Fig. 3). This condition is different from primitive actinopterygians that commonly lack supraorbital bones, or have only a single supraorbital bone (e.g. the so-called adnasal in Cheirolepis). CHEEK BONES The suborbital bones, preopercular, and dermohyal form the dorsal margin of the cheek (Figs 2, 3). Two suborbital bones are present anterior to the preoper-

7 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 601 Figure 5. Beishanichthys brevicaudalis gen. et sp. nov. (PKUP V4882, part and counterpart). Specimens in right and left lateral views, respectively. Scale bar: 10 mm. cular. They are roughly quadrangular in shape, although the upper ossification is slightly larger than the lower one. The presence of two suborbitals is also known in Fukangichtys, whereas other scanilepiforms (Scanilepis and Evenkia) have three or more suborbitals. The preopercular has an enlarged anterodorsal part located above the posterior extension of the maxilla, and a narrow posteroventral part between the maxilla and the subopercular. The preopercular canal runs upwards along the posterior margin, and has a branch that extends forwards at the median portion of this bone (Figs 2, 3). The angle between the posterior margin of the preopercular and the tooth-bearing margin of the maxilla is about 50, indicating an oblique suspensorium angle. In this condition, the new taxon is clearly different from crown-group neopterygians that have a vertical suspensorium (Gardiner, Schaeffer & Masserie, 2005). The dermohyal is a deep, triangular bone, contacting the opercular anteriorly (Figs 2, 3). A similar configuration is commonly seen in other primitive actinopterygians, but crown-group neopterygians have lost this bone entirely. The toothed maxilla and the subtriangular quadratojugal form the lower margin of the cheek (Figs 2, 3). The maxilla is of the usual palaeoniscoid type, having an elongate suborbital portion and a dorsoventrally expanded cheek portion. Dense striae are present on the external surface of the posterior expansion. These striae radiate posteriorly at the level close to the posterior border of the orbit. The maxilla bears at least 21 simple, conical teeth. These homodont teeth are almost equal in size and have an acrodin cap, as generally seen in other actinopterygians. The subtriangular quadratojugal is relatively large, contacting the maxilla anteriorly and the preopercular dorsally (Fig. 4B). A similar plate-like quadratojugal is also seen in other scanilepiforms (e.g. Scanilepis and Fukangichthys). In this character, the scanilepiforms are different from the perleidiforms

8 602 G.-H. XU and K.-Q. GAO Figure 6. Beishanichthys brevicaudalis gen. et sp. nov. A, PKUP V4881b, dorsal fin rays of caudal (note that scales failed to extend to caudal tip). B G, PKUP V4882, showing: anterior dorsal fin rays (B); ridge scales (C); posterior dorsal fin rays (D); caudal fin (E); flank scales (F); and ventral scales (G). H, composite reconstruction based on PKUP V , V4885. Scale bar: 3 mm. and crown-group neopterygians that have the quadratojugal greatly reduced or entirely lost. MANDIBLE The dentary is the largest bone of the wedge-shaped mandible, and is sutured with the angular posteriorly (Figs 2 4). It lacks a prominent coronoid process that is commonly present in crown-group neopterygians. The lower dentition is similar to that on the maxilla, with at least 23 pointed teeth that are roughly equal in height. The mandibular sensory canal is partly preserved along the dentary (Fig. 3). The enclosed pattern of this canal shows no difference in comparison with other actinopterygians. OPERCULO GULAR SERIES The opercular is high, trapeziform, and inclined anteriorly. The rectangular subopercular is as deep as the opercular. The external surfaces of the opercular and the subopercular are ornamented with dense striae. The interopercular is absent, as in all primitive actinopterygians, whereas crown-group neopterygians commonly have an interoptercular, with the exception of Lepisosteus that lost this bone secondarily (Olsen & McCune, 1991). Seven branchiostegal rays are preserved, and these are elongated as usual, as in other actinopterygians (Figs 2, 4). Scanilepis has between nine and 11 pairs of branchiostegal rays (Lehman, 1979), representing the largest number of this group. The branchiostegal rays are incompletely preserved in other known scanilepiforms, but there are at least three pairs in Fukangichthys (Su, 1978), six pairs in Evenkia (Sytchevskaya, 1999), and eight pairs in Tanaocrossus (Schaeffer, 1967). An elongate gular element is well preserved in the holotype, with its enlarged posterior portion being

9 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 603 Table 1. Measurements (in mm) Specimen (TL) SL BD (%SL) HL (%SL) HD (%SL) PPL (%SL) PVL (%SL) PDL (%SL) PAL (%SL) CPD (%SL) DFBL (%SL) AFBL (%SL) V4885 (81) (32.3) 16 (24.6) 21 (32.3) 18 (27.7) 34 (52.3) 27 (41.5) 47 (72.3) 8 (12.3) 37 (56.9) 10 (15.4) V4883 (135) (33.6) 35 (31.8) 36 (32.7) ~40 (36.4) 68 (61.8) 52 (47.3) 90 (81.8) 12 (10.9) 51 (46.4) 18 (16.4) V4881 (203) (36.6) 40 (25.0) 37 (23.1) ~45 (28.1) 113 (70.6) 66 (41.3) 125 (78.1) 20 (12.5) 84 (52.5) 30 (18.8) See text for definition of abbreviations. clearly visible (Fig. 2). This element is bilaterally asymmetrical, and is interpreted here as the lateral gular. The presence of this element is a different condition from that in the perleidiforms and crowngroup neopterygians, which commonly have a broad median gular, but lack lateral gulars. The median gular is unexposed in all the specimens, as a result of lateral compression of the skull; thus, the morphology of this element is unknown for the new taxon. The closely related Fukangichthys is known from threedimensionally preserved specimens that show the median gular is relatively smaller than that in the perleidiforms and crown-group neopterygians. PECTORAL GIRDLE The pectoral girdle includes the post-temporal, supracleithrum, postcleithrum, and cleithrum (Figs 2 4). The post-temporal is a subtriangular bone, located posterior to the extrascapular series (Figs 3, 4). The post-temporal sensory canal runs ventrally through the post-temporal, and enters the dorsal part of the supracleithrum. The supracleithrum is a deep element that contacts the post-temporal posteroventrally (Fig. 4). The postcleithrum is of a similar depth as the supracleithrum, and is located behind the supracleithrum cleithrum junction (Fig. 2). The large cleithrum is, as usual, L-shaped, as seen in other actinopterygians (Fig. 2). The clavicle is obscured by the branchiostegal rays, and is thus unexposed in all specimens. PAIRED FINS The pectoral fins are preserved in PKUP V4882 and PKUP V4884. The ten rays in the pectoral fin are segmented and branched distally (PKUP V4882; Fig. 5). The fringing fulcra are absent, as in all other scanilepiforms but Fukangichthys. The pelvic fin originates below the 11 th vertical scale row. Eleven fin rays are preserved in the pelvic fin of PKUP V4885. The pelvic fins of the other three specimens are incompletely preserved, with ten fin rays in PKUP V4882, and six in PKUP V4883 and V4884. The fin rays are segmented and distally branched. As in the pectoral fins, fringing fulcra are absent. MEDIAN FINS Similar to other scanilepiforms, Beishanichthys possesses a long-based dorsal fin with a lobe-shaped posterior margin (Figs 2 5). This has been recognized as a scanilepiform synapomorphy (Lehman, 1979; Sytchevskaya, 1999). The dorsal fin originates at the level of the 13 th vertical scale row, bearing 65 proxi-

10 604 G.-H. XU and K.-Q. GAO mally segmented fin rays, of which the anterior one or two short fin rays appear unbranched, whereas the rest are distally branched. The anal fin originates below the 22 nd vertical scale row, and has a lobe-shaped posterior margin. Of the 24 proximally segmented anal fin rays, the anterior four are short and unbranched, and the rest are long and distally branched (Fig. 6). The heterocercal caudal fin bears 18 fin rays, and has a slightly convex posterior margin (Figs 2, 5). The upper caudal fin rays (Figs 5, 6A) are proportionally longer than those of chondrosteans and other primitive actinopterygians. The ventralmost caudal fin ray stems from a position below the 39 th vertical scale row. Except for one or two fin rays at the dorsal and ventral margins, all other fin rays are distally branched. The short segments of median fin rays are ornamented with longitudinal striae. Similar ornaments are also present in other scanilepiformes, including Tanaocrossus (Schaeffer, 1967; Schaeffer & Donald, 1978: fig. 18), Fukangichthys (Su, 1978), and Scanilepis (Lehman, 1979). Similar to other scanilepiforms, fringing fulcra are absent in the median fins. SCALES The body is covered by large ganoid scales. A total of 42 vertical scale rows are present between the posterior margin of the pectoral girdle and the inversion of the caudal. Scales of the anterior flank are rectangular, and are twice as deep as wide. The depth of the scales decreases dorsally, ventrally, and posteriorly, and the scales become rhomboidal shaped in the caudal region. The flank scales have a straight posterior margin lacking any serrations. The scales of the median and posterior flank regions are twice as long as they are wide, and are smooth, whereas those of the dorsal and ventral regions are ornamented with ganoine ridges (Fig. 2). Ridge scales anterior to the dorsal fin total 15 in number, and each is ornamented by five ganoine ridges (Fig. 6C). The ventral scales anterior to the pelvis total about 20 in number, and each is ornamented with eight curved ganoine ridges (Fig. 6G). As commonly seen in other lower actinopterygians, the articular pegs and anterodorsal extensions are present on the flank scales (Fig. 6F). COMPARISON Relative to other scanilepiforms, the new taxon Beishanichthys is unique compared with all other known scanilepiforms in having 65 dorsal fin rays (vs. 150 in Scanilepis; > 70 in Evenkia; 74 in Tanaocrossus; ~80 in Oshia; ~50 in Fukangichthys, and ~100 in Mizhilepis) and a unique squamation formula (see diagnosis). As seen in Fukangichthys, it has two suborbitals (vs. three or more in Scanilepis and Evenkia). The presence of three supraorbitals is different from other scanilepiforms (four or more in Scanilepis and Evenkia), but the actual condition is still unknown for Fukangichthys. In addition, Beishanichthys is similar to Fukangichthys in having branched dorsal fin rays, whereas other known scanilepiforms (e.g. Scanilepis, Evenkia, and Tanaocrossus) have mostly unbranched dorsal fin rays. Considering other closely related scanilepiformes, Tanaocrossus was recently assigned by Milner et al. (2008) to the Perleidiformes, primarily based on the presence of an anterodorsally expanded preopercular and a purported vertical suspensorium. However, an anterodorsally expanded preopercular is plesiomorphic for actinopterygians. An acute angle between the posterior margin of the preopercular and the toothbearing border of the maxilla (G.-H. Xu, pers. observ.) is likely to indicate an oblique rather than vertical suspensorium of Tanaocrossus (new material of the taxon is under study by Andrew Milner and other authors; Milner pers. comm., 2008). Furthermore, the presence of the ethmoid sensory canal in the premaxilla, and a relatively large quadratojugal, are features excluding Tanaocrossus from the Perleidiformes. By contrast, published material clearly shows that Tanaocrossus possesses diagnostic character states of the Scanilepiformes, including: the presence of a longbased dorsal fin with a lobe-shaped posterior margin; the absence of basal and fringing fulcra; and an unforked caudal fin. None of these features are present in the Perleidiformes. Thus, it is concluded here that Tanaocrossus should be classified in the Scanilepiformes. PHYLOGENETIC ANALYSIS The Actinopterygii, the sister group to the Sarcopterygii, consist of three extant major clades: the Cladistia, Chondrostei, and Neopterygii (including Teleostei), and their closely related fossil forms (Patterson, 1982). The extinct Palaeonisciformes were traditionally classified as an order in the Chondrostei, which also included the Polypterini, Acipenseroidea, and Subholostei (Romer, 1945). This view has been abandoned, because cladistic analyses (Patterson, 1982; Gardiner, 1984; Gardiner & Schaeffer, 1989; Coates, 1999; Gardiner et al., 2005) have shown that the Palaeonisciformes are a paraphyletic group, and the Chondrostei, as the sister group of the Neopterygii, are now commonly treated as a higher group to include Acipenseriformes (crown-group Chondrostei), Birgeriidae, and Saurichthyiformes (stem-group Chondrostei) (Grande & Bemis, 1996; Bemis, Findeis & Grande, 1997; Gardiner et al., 2005).

11 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 605 The scanilepiforms have been traditionally misclassified in the Palaeonisciformes since Aldinger (1937), and their phylogenetic relationships with other lower actinopterygians have remained unresolved. For the first time this study, includes all the well-established scanilepiform taxa in a cladistic analysis to resolve the relationships among them, and their relationships with other major actinopterygian subclades. TAXON AND CHARACTER SELECTION The phylogenetic relationships of lower actinopterygians have been the subject of several studies over the past decades. Gardiner & Schaeffer (1989) made the first computer-assisted cladistic analysis of nonteleostean actinopterygians, based on a data matrix of 32 characters coded for 13 taxa, with Cheirolepis selected as the out-group. A decade later, Coates (1999) presented another analysis with the number of characters increased from 32 to 64, and the number of sampled taxa from 13 to 23. The latter analysis used a hypothetical ancestor as the out-group. Gardiner et al. s (2005) more recent analysis was largely based on data from Gardiner & Schaeffer (1989), but with an additional taxon (Kentukia), an increased number of characters (from 32 to 38), and with the acanthodian Acanthodes and sarcopterygian Eusthenopteron acting as two out-groups. Several other studies (e.g. Schultze & Cumbaa, 2001; Friedman & Blom, 2006; Long et al., 2008) were aimed at dealing with the interrelationships of primitive taxa of Devonian age, and were therefore less comprehensive than the phylogenetic analyses of Gardiner & Schaeffer (1989), Coates (1999), and Gardiner et al. (2005). Our phylogenetic analysis aimed to resolve the relationships of the new taxon Beishanichthys with other scanilepiforms, and the relationships of the Scanilepiformes with other actinopterygian clades. Given the aims of this study, our data set not only included all 13 taxa used by Gardiner & Schaeffer (1989), but also included four additional taxa (Kentukia, Mesopoma, Watsomulus, and Chondrosteus) selected from Coates (1999). In addition, four taxa (Fukangichthys, Evenkia, Scanilepis, and Beishanichthys) were selected as representatives of the Scanilepiformes. All of these genera are known from articulated specimens. Three other taxa (Tanaocrossus, Oshia, and Mizhilepis) were not included in this analysis because Tanaocrossus is being redescribed based on new material (A. Milner, pers. comm., 2008), and Oshia and Mizhilepis were based on poorly preserved specimens with a large number of anatomical uncertainties. Because a sister-group relationship between sarcopterygians and actinopterygians has been widely accepted (e.g. Schultze & Cumbaa, 2001; Zhu et al., 2009), the sarcopterygian Eusthenopteron was selected as the taxon for out-group comparison. A total of 72 characters (Appendix 1) were used in this study, including 62 adopted from previous publications (Gardiner & Schaeffer, 1989; Lund, Poplin & McCarthy, 1995; Bemis et al., 1997; Coates, 1999; Cloutier & Arratia, 2004; Gardiner et al., 2005; Hurley et al., 2007), and the addition of ten characters of our own (10, 15, 19, 21, 59, 60, 61, 62, 64, and 65). Of the 72 characters, nine are multistate and all remaindering characters are binary. Coding of these characters for the Chinese scanilepiforms was based on our own examination of the original specimens, and the codes for the following taxa were based on published literature: Eusthenopteron (Jarvik 1980); Cheirolepis (Gardiner 1967; Arratia & Cloutier 1996); Kentuckia (Rayner 1951); Mimia and Moythomasia (Gardiner 1984); Australosomus and Birgeria (Nielsen 1949); Boreosomus and Pteronisculus (Nielsen 1942); Perleidus (Stensiö 1921, 1932; Lehman 1952; Patterson 1975); Saurichthys (Stensiö 1925; Rieppel 1992); Watsonulus (Olsen 1984; Grande & Bemis 1998); Evenkia (Sytchevskaya 1999); Scanilepis (Lehman 1979); Acipenser (Bemis et al. 1997; Hilton 2005); Amia (Grande & Bemis 1998); Lepisosteus (Patterson 1975; Grande & Bemis 1998); Polypterus (Allis 1922; Otero et al. 2006). PHYLOGENETIC RESULTS AND DISCUSSION Parsimony analysis of the data set (Appendix 2) was conducted using the branch-and-bound algorithm of PAUP 4.0b10 (Swofford, 2003). All characters are equally weighted. Multistate characters were run as ordered to avoid possible loss of information (Merck, 1997; Wiens & Etheridge, 2003). The phylogenetic analysis resulted in five most parsimonious trees (tree length, TL = 159 steps; consistency index, CI = ; retention index, RI = ; rescaled consistency index, RC = ). The relationships of the actinopterygian subclades are discussed below based on the strict consensus of these five equally parsimonious trees (Fig. 7). Actinopterygii (clade A): The Actinopterygii have long been recognized as a natural group, and the monophyly of the group is well supported by a series of synapomorphies (e.g. Patterson, 1982; Gardiner & Schaeffer, 1989). Similar to other recent studies (Gardiner et al., 2005; Friedman & Blom, 2006; Long et al., 2008), this study intends to resolve relationships within the Actinopterygii, rather than to test the monophyly of the group. Nonetheless, the character states supporting the Actinopterygii (clade A) in this analysis include: 14 (1), 23 (1), 30 (1), 36 (1), 47 (1), and 63 (1). Within the actinopterygian clade, Cheirolepis (a fossil taxon known from the Middle Late Devonian) remains as the basal taxon, as recognized by previous

12 606 G.-H. XU and K.-Q. GAO Figure 7. Calibrated strict consensus of five most parsimonious trees, showing phylogenetic relationships and stratigraphic ranges of Scanilepiformes within the Actinopterygii. Character states supporting the clades include: A, 14 (1), 23 (1), 30 (1)*, 36 (1), 47 (1), 63 (1); B, 11 (1), 26 (1), 37 (1), 57 (1)*, 66 (1); C, 6 (1), 18 (1), 28 (1), 48 (1)*, 50 (1), 52 (1), 53 (1)*, 54 (1)*, 56 (1)*, 68 (1); D, 11 (2), 34 (1); E, 4 (2), 5 (1)*, 7 (1), 27 (1), 29 (1)*; F, 7 (2), 8 (1), 11 (3), 16 (1), 43 (1)*; G, 25 (1), 69 (1); H, 18 (0), 39 (1); I, 9 (1), 17 (1), 22 (1)*, 26 (0); J, 6 (0), 8 (0), 9 (2), 10 (1)*, 11 (4), 20 (1)*, 28 (1), 66 (0), 67 (1)*; K, 13 (1)*, 27 (0), 46 (2); L, 7 (0), 34 (0), 36 (0), 44 (1)*, 47 (0), 68 (0), 69 (0); M, 2 (1), 3 (1)*, 8 (2), 39 (0), 42 (1)*, 50 (0), 63 (2), 70 (1)*, 71 (1)*, 72 (1)*; N, 51 (1)*, 59 (1), 60 (1), 64 (1), 65 (1); O, 27 (2), 61 (1)*; P, 21 (1), 24 (1)*, 38 (1)*, 46 (1), 50 (1), 58 (1)*, 62 (1)*, 68 (0); Q, 2 (0), 19 (1)*, 25 (2), 28 (1), 31 (1)*, 35 (1), 41 (1)*, 49 (1), 64 (1); R, 1 (1)*, 27 (0), 32 (1)*, 33 (1)*, 45 (1)*. Character states with an asterisk have a consistency index of 1.0. Numerical values immediately below the nodes denote Bremer decay indices. analyses (Patterson, 1982; Gardiner, 1984; Gardiner & Schaeffer, 1989; Coates, 1999; Gardiner et al., 2005). The Cladistia (represented by Polypterus) is the sister group of the Actinopteri (clade C), supported by the following derived character states: 11 (1), 26 (1), 37 (1), 57 (1)*, 66 (1); character states denoted with an asterisk have CI = 1.0. As recognized by previous authors, the traditional grade taxon Palaeonisciformes is paraphyletic, because it includes stem-group actinopterygians (e.g. Cheirolepis), stem-group actinopterans (e.g. Mimia), and stem-group neopterygians (e.g. Australosomus), but not the crown-group neopterygians, as descendants. The clade Chondrostei is well supported as a monophyletic group that consists of the sister group of the Neopterygii (see below). Actinopteri (clade C): Diverging from the Cladistia, actinopterans emerged in the Late Devonian record with a suite of derived character states: 6 (1), 18 (1), 28 (1), 48 (1)*, 50 (1), 52 (1), 53 (1)*, 54 (1)*, 56 (1)*, 68 (1). Several taxa (Mimia, Moythomasia, Kentukia, Mesopoma, Boreosomus, and Pteronisculus) are recognized as stem-group members of the Actinopteri, as in Gardiner (1984) and Gardiner & Schaeffer (1989). Among these, Mimia is the most basal taxon of the Actinopteri. Moythomasia is more derived than Mimia, as it shares two derived character states with other crownward actinopterians: 11 (2), ascending process of parasphenoid terminating below spiracular canal; 34 (1), presence of supra-angular. Kentukia is more crownward than Moythomasia, as it shares several derived character states with clade F, including: 4 (2), enclosed spiracular canal; 5 (1)*, presence of fossil bridgei; 7 (1), paired posterior myodome; 27 (1), presence of suborbitals (or spiraculars); 29 (1)*, dermohyal separated from hyomandibular. More crownward

13 EARLY TRIASSIC SCANILEPIFORM FROM CHINA 607 than Kentukia is Mesopoma, which shares a set of synapomorphies with clade G, as follows: 7 (2), presence of median posterior myodome; 8 (1), single anterodorsal myodome; 11 (3), ascending process of parasphenoid meeting mouth of spircular canal; 16 (1), presence of supratemporal frontal contact; and 43 (1)*, ceratohyal consisting of two ossifications or cartilages. Further up the tree, Mesopoma is followed by Pteronisculus, which shares two synapomorphies with clade H: 25 (1), three infraorbitals; and 69 (1), hypophysis and enclosing recess in neurocranium projecting ventrally or anteroventrally. The last stem-group member of clade C is Boreosomus, which shares two synapomorphies with crown-group Actinopteri (clade I): 18 (0, reversal), dermosphenotic separated from nasal; 39 (1), absence of canal for hyoid branch of nerve VII in hyomandibular. All crown-group members of the Actinopteri (clade I) share the following derived character states: 9 (1), parasphenoid extending across otic fissure; 17 (1), absence of intertemporal; 22 (1)*, antorbital separated from premaxilla; and 26 (0, reversal), presence of supraorbital bones. The Chondrostei (clade J) consist of the sister group of the Neopterygii (clade M) within the crown-group Actinopteri. Chondrostei (clade J): The monophyly of the Chondrostei (including Birgeria and Saurichthys) is supported by the following synapomorphies: 6 (0, reversal), absence of lateral cranial canal; 8 (0, reversal), paired anterodorsal myodome; 9 (2), parasphenoid extending to basioccipital; 10 (1)*, absence of parabasal canal; 11 (4), ascending process of parasphenoid partly overlapping orbitotemporal and otic regions; 20 (1)*, course of ethmoid commissure through bone centre of premaxilla; 28 (1), absence of dermohyal; 66 (0, reversal), absence of peg-and-socket articulation of scales; and 67 (1)*, reduced flank scales. Birgeria is the most basal taxon of the Chondrostei, and Saurichthys is the sister group with the Acipenseriformes (clade L, crown-group Chondrostei), as recognized by Gardiner et al. (2005). More derived than Birgeria, Saurichthys shares with the Acipenseriformes two synapomorphies: 13 (1), presence of craniospinal process; 46 (2), absence of gular bones. Neopterygii (clade M): Diverging from the Chondrostei, the Neopterygii emerged in the Early Triassic fossil record, and show a long list of derived character states: 2 (1), presence of subtemporal fossa; 3 (1)*, presence of dilatator fossa; 8 (2), absence of anterodorsal myodome; 42 (1)*, epibranchials 1 and 2 with strongly forked ends (uncinate processes); 39 (0, reversal), presence of canal for hyoid branch of nerve VII in hyomandibular; 42 (1)*, presence of strongly forked ends (uncinate processes) in epibranchials 1 and 2; 50 (0, reversal), absence of fringing fulcra; 63 (2), hemi-heterocercal caudal fin with longer upper caudal fin rays; 70 (1)*, undivided cerebellar corpus; 71 (1)*, cerebellar corpus arching above fourth ventricle; 72 (1)*, median anterior projection on cerebellar corpus. Within the Neopterygii, an unresolved polytomy involves Australosomus, the clade N (Scanilepiformes), and the clade P (Perleidus plus crowngroup Neopterygii). Scanilepiformes (clade N): The monophyly of this clade is supported by the following character states: 51 (1)*, the presence of longitudinal striated ornament on short segments of median fin rays; 59 (1), a long-based dorsal fin composed of more than 50 fin rays; 60 (1), a dorsal fin with a lobe-shaped posterior margin; 64 (1), a caudal fin with an unforked posterior margin; 65 (1) an anal fin with a lobe-shaped posterior margin. Within the Scanilepiformes (clade N), Scanilepis and Evenkia are recognized as sister groups, and this grouping (clade O) is supported by two derived character states: the presence of three suborbitals 27 (2), and most of their dorsal rays being unbranched 61 (1)*. Two other scanilepiforms (Beishanichthys and Fukangichthys) form a polytomy with the clade O. Perleidiformes plus crown-group Neopterygii (clade P): Clade P is supported by the following character states: 9 (1), parasphenoid extending across otic fissure; 21 (1), absence of sensory canal in premaxilla; 24 (1)*, premaxilla with nasal process; 38 (1)*, horizontal hyoid facet; 46 (1), absence of lateral gulars; 50 (1), presence of fringing and basal fulcra; 62 (1), dorsal and anal fin rays segmented distally; 68 (0, reversal), optic tectum smaller than telencephalon. Within the clade, Perleidiformes (sampled taxon Perleidus) form the sister group of the crown-group Neopterygii (clade Q). Crown-group Neopterygii (clade Q): The crown-group neopterygians share the following derived character states: 2 (0, reversal), absence of subtemporal fossa; 19 (1)*, absence of rostral(s) frontal contact; 25 (2), presence of four or more infraorbitals; 28 (1), absence of dermohyal; 31 (1)*, maxilla free from preopercular; 35 (1), presence of coronoid process; 41 (1)*, presence of symplectic; 49 (1), absence of clavicle; and 64 (1) posterior margin of caudal fin unforked. In general, Beishanichthys and other scanilepiforms lack the derived character states that diagnose the Perleidiformes, or those supporting the grouping of the Perleidiformes, with the crown-group neopterygians; thus, the Scanilepiformes cannot be placed in the Perleidiformes, nor near the origin of the Amiidae (contra Lehman, 1979; Milner et al., 2008).

14 608 G.-H. XU and K.-Q. GAO PALAEOECOLOGICAL REMARKS The new fossil discovery from the Beishan site documents the oldest known record so far of the Scanilepiformes in China. It extends the geological distribution of this group in China from the Upper Triassic of Shaanxi (Mezhilepis), Middle Triassic of Xinjiang (Fukangichthys), to the Lower Triassic of Gansu Province. Similar to fossils of closely related taxa from North America and Siberia, the new taxon and all other Chinese scanilepiforms were preserved in freshwater deposits. The occurrence of scanilepiform fossils in marine deposits was only known from Late Triassic beds, represented by a single genus Scanilepis from Sweden. Considering the evidence available so far, it is reasonable to interpret that the Scanilepiformes probably originated at a time no later than the Early Triassic, in freshwater environments of the northern continent, and the Late Triassic marine record represents a secondary invasion close to the end of the evolutionary history of the clade. The fossil locality in Beishan Hills has been extensively quarried for four field seasons ( ), and more than 2000 fish specimens were collected from the same horizon. Most specimens from this locality are completely preserved without notable biological disturbance, indicating an event of mass mortality. Beishanichthys is known from large specimens up to 700 mm in length. However, there were only six (out of more than 2000 actinopterygian specimens) that could be ascribed to this taxon. Considering the taphonomic nature and the multiple-year field collection at the locality, it is unlikely that the relatively small number of specimens of Beishanichthys reflects a sampling bias; instead, it may well indicate a lower abundance of individuals of this genus compared with fish belonging to other taxa in the same assemblage. Results of our phylogenetic analysis recognize Scanilepiformes as a stem-group clade in the Neopterygii. Having a characteristic long-based dorsal fin with a lobe-shaped posterior margin, scanilepiforms represent a morphological specialization of stem neopterygians. Although the extant neopterygian Amia also has a long-based dorsal fin, the phylogenetic analysis indicates convergent acquisition of this character state in this extant taxon and the extinct scanilepiforms. Considering the functional morphology of median fins, scanilepiforms were probably not fast swimmers as had previously been suggested by Schaeffer (1967). They might have similar ecological adaptations as the crown-group neopterygian Amia, as a sluggish swimmer in quiet backwaters (Etnier & Starnes, 1993; Grande & Bemis, 1998). With sharp teeth along the oral margin, scanilepiforms seem to have been voracious and opportunist feeders. The Scanilepiformes emerged in the fossil record in the Early Triassic, but became extinct at the end of that period. The Triassic Jurassic transition, in association with the break-up of the supercontinent Pangaea, is inferred as a catastrophic event (Ward et al., 2001; Olsen et al., 2002). The cause of this Late Triassic extinction may involve multiple factors, including sea-level fluctuations, mass volcanic eruptions, and asteroid impact (e.g. Hallam & Wignall, 1997; McElwain, Beerling & Woodward, 1999; Ward et al., 2001; Olsen et al., 2002). This extinction also involved other stem-group neopterygians, conodonts, all large non-dinosaurian archosaurs, some therapsids, and many groups of large amphibians (Benton, 1994; Hallam & Wignall, 1997). More derived neopterygians (e.g. caturids and pholidophorids) survived the extinction event, and became dominant in terms of both diversity and individual abundance in the Early Jurassic. ACKNOWLEGEMENTS We thank Martha Richter (Natural History Museum) and an anonymous reviewer for their helpful review of an early version of the manuscript. Thanks are extended to Wang Zhao for the latex peels of the specimens and Gao Wei for specimen photography. This research was supported by the National Natural Science Foundation of China (NSFC grants , , and ), and the China Postdoctoral Science Foundation (CPSF ). At a later stage of this research, G.-H. 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