Sinosaurichthys longipectoralis, Feixiang & Yuanlin & Guanghui & Weicheng & Dayong & Zuoyu, 2011

Feixiang, Wu, Yuanlin, Sun, Guanghui, Xu, Weicheng, Hao, Dayong, Jiang & Zuoyu, Sun, 2011, New saurichthyid actinopterygian fishes from the Anisian (Middle Triassic) of southwestern China, Acta Palaeontologica Polonica 56 (3), pp. 581-614 : 583-595

Sinosaurichthys longipectoralis sp. nov.

Figs. 3–9.

Etymology: From Latin longus and pectoralis, referring to its exceptionally elongated pectoral fins.

Type material: Holotype GMPKU−P1233 , a laterally compressed skull with part of the postcranial skeleton . Paratypes: GMPKU−P1214 , a postcranial skeleton with complete caudal region; and GMPKU−P1215 , a laterally compressed skull .

Type locality: Yangjuan Village , Xinmin, Panxian County, Guizhou Province, China .

Type horizon: The vertebrate fossiliferous horizon in the Upper Member of the Guanling Formation (Pelsonian of Anisian, Middle Triassic) ( Sun et al. 2006).

Referred specimens.—GMPKU−P1089, 1097, 1099, 1126, 1141, 1183, 1211, 1223, 1225, 1227, 1234, 1247, 1253, 1361, 1362, 1366.

Diagnosis.— Type species of Sinosaurichthys , pectoral fin sickle−shaped and extremely long, reaching about or more than mandible length; cleithrum bearing anteriorly inclined dorsal stem and rather deep posterior blade with depth/length ratio about 1.8; posttemporal−supracleithra meeting at midline; pelvic fin relatively long; axial skeleton consisting of no less than 210 neural arches between opercle and caudal fin (compared with 157–172 in S. longimedialis and 154–156 in S. minuta described below), including ca. 180 anterior ones with neural spines; at least 90 mid−dorsal scales anterior to dorsal fin. Fin formula: P 24–25, V 23–24, D/A ~55/~50, C 36–38/36–38.

Description

General appearance.—As a shared feature of the Saurichthyidae , Sinosaurichthys longipectoralis has a long rostrum and an elongated, slender body. The standard length of the largest specimen is over 560 mm. The skull length is 27% of the standard body length. The rostrum makes up 73–76% of the mandible length ( Figs. 3A–C, 4; Table 1). It is similar to other members of the same genus described below in having the pectoral fins located near to the posterodorsal corner of the opercle, in contrast to Saurichthys that have pectoral fins much lower located as commonly in other actinopterygians. The pelvic fins are closer to the caudal fin than to the opercle. The dorsal and anal fins are opposite to each other and are much closer to the pelvic fins than to the caudal fin.

Endocranium.—The endocranium is poorly ossified and only the posterodorsal part of the orbitotemporal region was preserved in some of laterally compressed specimens to carry two foramina ( Fig. 4A), probably related to the oculomotor nerve (III).

Snout.—The snout is composed of the paired rostro−premaxillae and nasalo−antorbitals, with a length up to 61–65% of the skull length ( Fig. 4). The rostro−premaxilla is elon−

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gated and triangular, tapering anteriorly and carrying the ethmoid commissure at its anterior tip. The rostro−premaxilla meets its opposite pair medially and contacts with the frontals and nasalo−antorbitals posterodorsally, and the maxilla posteriorly, with a series of conical teeth along its oral margin ( Figs. 4, 5 ). The rostro−premaxilla is ornamented with parallel striations, dipping posteroventrally, and a few tubercles near its dorsal edge. The nasalo−antiorbital is triangular, in contact with the frontal dorsally and the rostro−premaxilla ventrally, and forms the anterior rim of the orbit. Two subovate external nares are present on this bone, arranged in the same way as in other saurichthyids, and the anterior one is distinctly larger than the posterior. The supraorbital sensory canal enters the nasalo−antorbital from the frontal and passes between the two nares to join the infraorbital sensory canal at the ventral portion of this bone. The nasalo−antorbital is ornamented with posteroventrally inclined striations and patch of tubercles near the dorsal edge.

Dermal skull roof.—The skull roof consists of paired frontals, parietals, dermopterotics and extrascapulars ( Figs. 4, 5A, C ). The frontals are elongated and triangular, tapering anteriorly and forming the main part of the anterior portion of the skull roof above the orbit. Posteriorly, the frontals are in contact with the parietals and dermopterotics. The parietals are subcircular and relatively large in proportion to the skull width, with a width about 60% of the skull width ( Fig. 5A, C ). The dermopterotics compose the major part of the posterior portion of the skull roof. The posterior end of the dermopterotic is located at the level of the anterior margin of the opercle. As a characteristic feature of this family, the dermopterotics meet at the mid−line of the skull roof posterior to the parietals with a distinct notch at the anterolateral margin of the bone on each side ( Figs. 5A, C , 6A ) which was interpreted to accommodate the opening of the spiracle canal in Saurichthys ( Stensiö 1925) . The dermopterotic has a posterolaterally protruding process as the articular facet for the extrascapular and posttemporal−supracleithrum. The part of the dermopterotic anterior to the notch is laterally bent downward to form a triangular doi:10.4202/app.2010.0007

lateral lobe to cover part of the cheek region between the orbit and the preopercle. The extrascapulars are small and subovate ( Figs. 3A, 4A, 5C ). The external surface of the skull roof is ornamented with dense tubercles.

Cheek and opercular series.—The orbit is subcircular to ellipse shaped. Similar to Saurichthys curionii ( Rieppel 1985) , no supraorbital bones are developed and the frontal directly forms the dorsal margin of the orbit ( Figs. 4, 5A, C ). The dermosphenotic is a small slender bone, forming the posterodorsal margin of the orbit. The infraorbital sensory canal extends upward in the posterior half of this bone to enter the dermopterotic. The infraorbitals are poorly preserved and only a few fragments can be identified along the posterior and ventral margins of the orbit in the holotype ( Fig. 4A). The sclerotic ring is partly exposed along the edge of the orbit in several specimens. The ring probably has four ossification centers because three elements are exposed in GMPKU−P1183 which occupies almost 3/4 of the orbital circumference ( Fig. 6A ).

The postorbital region is rather short, with a length evidently less than the skull depth, differing from that in most known species of Saurichthys ( Stensiö 1925; Rieppel 1985) in which the length of the postorbital region is generally greater than or equal to the skull depth. The maxilla and preopercle are the main dermal elements of the cheek region. The maxilla is composed of a long and slender anterior orbital portion that contacts the rostro−premaxilla anteriorly and a highly expanded postorbital portion that contacts with the preopercle. The oral margin of the maxilla is slightly concave behind the orbit. The preopercle is deep and almost vertical, with a distinct concave anterior margin. The dorsal portion is expanded and ventral portion is narrowed, showing a primitive condition as commonly in other lower actinopterygians ( Fig. 4A, C). The quadratojugal is relatively small, in contact with the maxilla anteriorly and the preopercle dorsally ( Fig. 4A), showing more or less a plesiomorphic condition as in other lower actinopterygians (e.g. Mimia , Moythomasia , Pteronisculus , and Birgeria ) ( Nielsen 1942, 1949; Lehman 1952; Gardiner 1984). This bone is greatly deduced or lost in neopterygians such as Amia ( Grande and Bemis 1998) .

As a shared feature of the Saurichthyidae , Sinosaurichthys longipectoralis has a single large, semicircular opercle and lacks an independent subopercle ( Figs. 3A–C 1 , 4A, B 1 , C). The opercle reaches 85–88% of the skull depth in height, with a depth/width ratio varying from 1.55 to 1.97 (average 1.76; Table 2). A small process is developed in its straight anterior margin at the level slightly higher than the joint of the upper and lower jaws. Externally the opercle shows radiating and concentric striations with some tubercles near its dorsal and ventral edges. The medial side of the opercle is smooth except for a distinct circular recess posterior to the process +

mentioned above. Neither gular plates nor branchiostegal rays are developed. In Saurichthys , the gular plates are absent but there is generally one pair of branchiostegal rays.

Mandible.—The elongated lower jaw is as long as the upper jaw. Its maximum depth is less than half of the skull depth. The symphyseal region occupies about two fifth of the mandible length. There is little difference in the arrangement of the dermal elements in lateral side of the mandible from that of most species of Saurichthys ( Fig. 4A, B 1 , C). The dentary is the largest ossification and covers almost the whole lateral side of the mandible. It is ornamented with anteroventrally inclined fine striations and a few tubercles along the ventral edge. The angular is triangular, occupying the posteroventral portion of the mandible and sutures with the dentary anterodorsally ( Fig. 4A, B 1 , C). In the lateral side, the angular extends to the level anterior to the posterior rim of the orbit, whereas ventrally the bone bends up dorsomedially to wrap the mandible along its ventral edge and continues forward beyond the anterior rim of the orbit. The angular is ornamented with coarse ridges that radiate from its posteroventral corner, and some tubercles along its posterior and ventral edges. The supraangular is a small slender element, located at the posterodorsal corner of the mandible anterior to the articular.

In the lingual side of the mandible a long bone with many small teeth can be seen in specimen GMPKU−P1141, covering almost the whole length of the mandible ( Fig. 5B ). It should be the fused prearticular and coronoids (= mixcoronoid of Stensiö 1925). It is roughly acute triangular, high in the posterior part and tapering anteriorly, with a straight dorsal edge. The posterior part of this bone contacts the angular posteroventrally ( Fig. 5B ). In the joint region with the upper jaw, there are two transverse depressions related to the articulation with the quadrate; therefore this region should be the ossification of the articular, similar with the situation in some other known saurichthyids ( Stensiö 1925; Beltan 1968; Rieppel 1985). The adductor fossa is elongated and deep, enclosed laterally by the dentary and supraangular, medially by the prearticular−coronoid, and posteriorly by the articular ( Fig. 5B, E ).

Palate.—The palate includes a pair of long and slender vomers ( Fig. 6C, E ), and a median parasphenoid. Although the parasphenoid is incompletely preserved in all specimens, its general morphology and structure can still be restored ( Fig. 6D ). As in the Lower Triassic Saurichthys from Spitsbergen and Madagascar ( Stensiö 1925; Beltan 1968), the parasphenoid consists of a long anterior stem that has extended between the paired vomers, a pair of large ascending processes that have dorsolaterally extended to cover considerable portion of the otic and orbitotemporal regions of the neurocranium, and a posterior stem that has extended posteriorly over the occipital region. It shows the following features that differ from that of Saurichthys described by Stensiö (1925): (1) the posterior stem is highly elevated above the mid−point of the skull depth with a high plate−like ventral crista ( Fig. 6A, B, D ) while in Saurichthys it is only slightly elevated with a low ridge−like ventral crista. The elevation of the pos−

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terior stem of the parasphenoid in Sinosaurichthys is apparrently related to the elevation of the axial skeleton in the abdominal region and is unique; (2) the tooth plate or patch in the ventral (oral) face of the parasphenoid extends posteriorly on the ventral crista posterior to the ascending process while that in Saurichthys is relatively short, and only restricted anterior to the ascending process; (3) the anterior stem is very long, about three times of the length of the posterior one ( Fig. 6C–E ) while in the Lower Triassic Saurichthys the anterior stem is almost as long as the posterior one. But in some later representatives of Saurichthys the anterior stem may be longer than the posterior one because this feature is evidently related to the shortening of the postorbital region in the saurichthyids; (4) the efferent pseudobranchial arteries penetrate the parasphenoid through a pair of small ear−like processes anterior to the ascending process ( Fig. 6A, B, D ). This paired ear−like process, more or less, resembles to the dermal basipterygoid process in some low actinopterygians in morphology and position but it leaves no trace for articulating with the palatoquadrate. Maybe it represents an incipient or highly reduced basipterygoid process. A similar condition is present or probably present in some of the Middle Triassic Saurichthys , such as Saurichthys dawaziensis ( Wu et al. 2009) and S. curionii ( Rieppel 1985) but probablly absent in the Early Triassic Saurichthys ( Stensiö 1925) ; (5) the foramina of the common carotid arteries are situated in the lateral wall of the ascending process with openings directed more or less lateroventrally ( Fig. 6A, B, D ). In Saurichthys ornatus the same foramina (originally interpreted as for the external carotid arteries by Stensiö (1925), and later assumed to have transmitted the common carotid arteries by Patterson (1975) are in the underside of the parasphenoid beneath the posterior margin of the ascending process ( Stensiö 1925) and in S. curionii they are even anterior to the ascending process ( Rieppel 1985).

Hyoid arches.—The hyomandible is almost vertical, having a slightly broad, blade−like dorsal portion and a narrow, slen− der posteroventral portion ( Figs. 5B , 6A, B, F 1 ), slightly different from the hockey stick−like one in Saurichthys hamiltoni ( Stensiö 1925) and S. costasquamosus ( Rieppel 1985) . The blade−like dorsal portion has a distinct posteroventrally directed ridge running through its medial surface and the posteroventral portion seems to contact with the palatoquadrate at a point slightly high above the mandibular articulation. No opercular process is present in the hyomandible. The symplectic is absent as in Saurichthys and other lower actinoptergyians. The ceratohyal can be seen in GMPKUP1215 and 1253, being of a typical hour glass shape, narrow rod−like in the middle and expanded plate−like at the two ends ( Figs. 4B 1 , 6F 2 ).

Palatoquadrate complex and related dermal bones.—Only the qudratometapterygoid portion of the palatoquadrate is ossified and can be observed in two specimens. The posteroventral part of the quadratometapterygoid portion is well ossified, rather thick and condense, to articulate with the lower jaw ( Fig. 3C 1 ), and the dorsal part of this portion occurs as thin perichondral doi:10.4202/app.2010.0007

lining ( Fig. 5B ). Three dermal bones contacting the palatoquadrate ventromedially, i.e., the dermopalatine, ectopterygoid and entopterygoid can be distinguished ( Figs. 5A, B , 6A, C ). The dermopalatine is roughly obtuse triangular to trapezoid in outline, in contact with the vomer anteriorly, with the parasphenoid medially and with the maxilla laterally. Posterior to the dermopalatine, the ectopterygoid contacts the ventromedial edge of the maxilla ventrally. Medially, it is in contact with the entopterygoid and posteriorly forms the anterior margin of the adductor fossa of the upper jaw. The entopterygoid is roughly triangular and tapers forward along the dorsal edges of the dermopalatine and ectopterygoid.

Dentition.—There is a single row of large teeth on the oral margin of the upper and lower jaws, arranged in the same pattern as in Saurichthys curionii ( Rieppel 1985) , with small ones in between and around ( Fig. 3C 2 ). The oral surfaces of the vomer, parasphenoid, dermopalatine, ectoperygoid, entopterygoid, and prearticular−coronoid are covered by small teeth. The large teeth are relatively smaller than those in Saurichthys . In adult specimens the diameter of the large teeth is 0.25–0.6 mm at the base and its depth 0.45–0.86 mm, with the depth/width ratio ranging from 1.7–2.1. All teeth are conical, with a semitransparent enamel acrodin cap that is slightly over one−third of the tooth depth. Numerous faint vertical striations exist in the basal part of the teeth.

The depressions for receiving the tips of the large teeth of the upper jaw can be seen in the anterior part of the lower jaw lateral to the tooth row. These “incissivlücken” are also known in some other saurichthyids, such as Saurichthys krambergeri ( Griffith 1962) , Saurichthys dawaziensis ( Wu et al. 2009) , and an undetermined species of Saurichthys from the Eotrias of South Africa ( Griffith 1978), and in the Early Jurassic saurichthyid genus Acidorhynchus ( Gardiner 1960; Thies 1985).

Paired fins and girdles.—The pectoral fins and girdles are preserved almost in the original articulated state in the holotype ( Figs. 3A, 4A), showing a condition that the pectoral fins are much more dorsally inserted than those in Saurich−

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thys. Although most of the fin rays were weathered away, their impressions remain on the matrix. The bases of the fin rays are arranged in an arc that slightly curves down backward dorsal to the radials. The fins are sickle−shaped, as long as or longer than the mandible length. The longest pectoral fins are recorded in GMPKU−P1097, reaching 257 mm long, about 1.84 times of the mandible length. In Saurichthys the pectoral fins are generally fan−shaped, with a length generally no more than 1/6 of the mandible length. No segmentation is observed in the fin rays. The anterior four to five fin rays are unbranched and the remainder branch distally five times maximally and twice minimally. The 7 th fin ray is the longest.

The dermal elements of the pectoral girdle are well preserved ( Figs. 3A–C 1 , 4, 7A, B ). The posttemporal (= suprascapular sensu Stensiö 1925; Lehman 1952; Rieppel 1980) and supracleithrum are fused into a large bone (here tentatively named as posttemporal−supracleithrum) consisting of a rectangular, horizontal dorsal portion (= posttemporal) and a triangular, vertical ventrolateral portion (= supracleithrum) posterior to the dermopterotic and extrascapular and dorsal to the opercle. The dorsal portion of the bone meets its fellow of the opposite side at the midline and the ventrolateral portion of this bone is partially overlapped by the opercle ventroanteriorly and contacts the cleithrum posteriorly. The pores of the infraorbital sensory canal can be seen distributed along the border of the two portions of this bone to extend anteriorly into the dermopterotic and runs posteriorly into the body. The exposed surface of this composite bone is ornamented with tubercles and the area overlapped by the opercle has longitudinal ridges with serrations pointing upwards. The postcleithrum is absent. The cleithrum is boot−shaped and consists of a deep rectangular posterior blade, a long, slender and curved dorsal stem, and a short horizontal anteroventral arm ( Figs. 3A, 4A, C, 7A 2 , A 3, D), different from the typical triradiate one in other saurichthyids. The bone is concave anteriorly and borders the posterior margin of the opercle. The anterodorsal tip of the dorsal stem articulates with the posttemporal−supracleithrum. The depth of the posterior blade of the bone is more than half of the skull depth with a depth/length ratio of about 1.8. The horizontal anteroventral arm is low, with its anterior edge concave to fit the posterior margin of the clavicle. A prominent keel in the medial surface runs from the radiation center of the bone upward to the tip of dorsal stem. The clavicle is suboval to subtriangular ( Figs. 3A, 4A, 7A 4, A 5 ), with its expanded posterior end articulating with the cleithrum, ventral to the opercle ( Fig. 7D ). The exposed surfaces of the cleithrum and clavicle are decorated with spiny tubercles while the areas overlapped by the opercle are ornamented by similar ridges to those on posttemporal−supracleithrum with serrations pointing away from the opercle ( Fig. 7C ).

The endoskeletal pectoral girdle is best preserved in the holotype, including the scapulocoracoid and the radials. The scapulocoracoid is a deep plate−like structure emerging behind the dorsal stem of the cleithrum. It bears at least seven radials along its dorsal margin. Except the anteriormost and largest one, the rest decrease gradually in size posteriorly. These radials support approximately 25 fin rays distally ( Figs. 3A, 4A, 7D ).

The pelvic fins are situated closer to the caudal fin than to the pectoral ones, with its distance to the caudal fin slightly more than one−third of the distance between the opercle and the caudal fin. Compared to Saurichthys and other species of Sinosaurichthys , the pelvic fins are quite long, more than the skull depth ( Table 2). In Saurichthys and other two species of the new genus, the pelvic fins are generally less than or as long as half of the skull depth. Each pelvic fin consists of 23–24 unsegmented, distally branched fin rays that articulate with the posterior edge of the pelvic bone ( Fig. 7E, F ). The pelvic bone is subrectangular. No radials are preserved.

Unpaired fins.—The unpaired fins are relatively well preserved in three specimens. The dorsal and anal fins are triangle−shaped and situated opposite to each other, slightly posterior to the pelvic fins ( Fig. 3D). The depth/width ratio of the dorsal and anal fin is over 1.7, showing a higher aspect ratio (defined as depth 2 /area) than that in Saurichthys and the other two species of Sinosaurichthys . The estimated fin rays of the dorsal and anal fin in GMPKU−P1214 are no less than 55 and 50, respectively. The anterior 12 fin rays are stout and unbranched, whereas the following ones are distally branched once or twice. The 12 th fin ray is the longest. Generally, a maximum of three to four segments are counted in the longest fin ray of both the dorsal and anal fins, but six segments are recorded in the anal fin in GMPKU−P1223. Both the dorsal and anal fins are supported by the radials consisting of slender proximal axonosts and small distal baseosts. There are 16 axonosts on each fin. The axonosts are posterodorsally and anterodorsally directed in the dorsal and anal fin, respectively, and tend to decrease in depth posteriorly. The small and rectangular baseosts are poorly ossified, lying distal to the axonosts.

The caudal fin is deeply forked and symmetrical, with 36–38 fin rays in each lobe directly supported by the axial endoskeleton and with an angle between the leading edges of the two lobes varying from 84 ° to 100 °. There are at least six segments in the epichordal lobe and five segments in the hypochordal lobe of the caudal fin with maximal three times of distal bifurcation in GMPKU−P1089. The depth of the caudal fin is about 2.8 times of the maximal body depth in GMPKU−P1214.

The basal and fringing fulcra are present in all median fins. Six to seven basal fulcra can be seen in the anal fin in GMPKUM−P1214 and P−1122. Two to three basal fulcra exist on each lobe of the caudal fin. The fringing fulcra occur as small spine−like elements lying on the surface of margin leading rays distally, distinctly shorter than the basal fulcra and overlapping one by one. This condition probably can be assigned to the pattern B as proposed by Arratia (2008: 229).

Axial skeleton.—The axial skeleton consists of the neural and haemal arches applied to the persisting notochord. In GMPKU−P1099, approximately 140 and 70–72 neural arches exist in front of the pelvic fins and between the pelvic and caudal fin, respectively. In GMPKU−P1234, 140–150 neural arches are estimated in front of the pelvic fins. Thus, the total number of the neural arches in the trunk is no less than 210 and this figure does not include the ones hidden by the opercle and those (approximately 14–18) supporting the fin rays of the epichordal lobe of the caudal fin. The neural arches are paired structures. In their medial face there is a sulcus parallel to the longitudinal axis of the notochord ( Fig. 8D–F ). The sulcus, together with its counterpart in the neural arch of the opposite side, is supposed to form the canal for the spinal cord. A small foramen, probably related to the spinal nerve or intersegmental vessel, can be observed in the sulcus of every other neural arch all through the axial skeleton in some specimens ( Fig. 8D–F ), suggesting that one neural arch corresponds to only half sclerotome or one dorsal arcualian element (basidorsal or interdorsal). Each neural arch carries a prae− and a postzygapophysis along its dorsal edge. When in articulation, each praezygapophysis overlaps the postzygapophysis of its preceding neural arch ( Fig. 8A 1 , F). Each neural arch is expanded at its ventral base ( Fig. 8A 2 –F ) with an acetabula−like concavity, presumed to house the cartilaginous part of the dorsal arcualia elements which rest on the dorsolateral aspect of the notochord. The elongated paired neural spines are developed distally to all the neural arches ante−

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rior to the caudal peduncle and the following 28 neural arches anterior to the caudal fin do not carry neural spines, and thus look “T” shaped in lateral view ( Fig. 8A 2 ). When approaching the caudal fin, the neural arches support the fin rays of the epichordal lobe of the caudal fin.

The haemal arches are paired and lie along the ventrolateral aspects of the notochord, opposite to the neural arches ( Fig. 8A 1 ). The haemal arches occur as poorly ossified small suboval plates in the abdominal region and consist of two kinds of alternatively arranged bony plates in the caudal region. One of them is well ossified and considerably large, almost corresponding to two neural arches in length and bearing a distinct haemal spine, and the other is poorly ossified and very small, without a haemal spine. These two kinds of haemal arches should represent the separate basi− and inter−ventral arcualia elements ( Fig. 8A 1 ). Nearly twenty haemal arches with distinct haemal spines can be counted between the pelvic and anal fin in GMPKU−P1214.

Based on the size relationship of haemal and neural arches in Saurichthys ornatus, Stensiö (1925) supposed that the basidorsal and interdorsal elements are equally developed and possess the same shape in Saurichthys , but this viewpoint was not widely accepted. The presence of the foramen of the intersegmental vessels in the haemal arches of Saurichthys madagascariensis ( Lehman 1952) , and one haemal arch corresponding to one neural arch in Saurichthys curionii ( Rieppel 1985) had led to the idea that the neural arches of the saurichthyids represent only the basidorsals ( Arratia et al. 2001). However, the alternative distribution of the foramen in the neural arch in Sinosaurichthys longipectoralis and in Saurichthys dawaziensis ( Wu et al. 2009) provides evidence to support Stensiö’s (1925) hypothesis and strongly suggests that the neural arches in saurichthyids, at least in some species of Saurichthys and Sinosaurichthys are alternate basidorsal and interdorsal. In other lower actinopterygians, the ossification of basidorsal is always larger than the interdorsal and neural spines are usually only developed in the basidorsals. Consequently, the basidorsal and interdorsal equally−developed should be considered as a possible synapomorphy of the saurichthyids.

Squamation.—Similar to the Middle Triassic Saurichthys from Monte San Giorgio ( Rieppel 1985, 1992) but different from the species of Saurichthys of other areas of the world, Sinosaurichthys bears six longitudinal rows of scales, including one mid−dorsal, one mid−ventral, two mid−lateral and two ventrolateral rows. In the GMPKU−P1126, in addition to the six rows, numerous small bony plates are scattered between the scale rows.

The mid−dorsal scale row runs through the body length and only interrupted by the dorsal fin. Because of the incomplete preservation, in specimen GMPKU−P1099, 81 mid−dorsal scales can be counted only between the skull and the level slightly posterior to the pelvic fins. In the other two specimens, 16–17 mid−dorsal scales can be counted in the area between the pelvic and dorsal fins. Thus, the total number of the mid−dorsal scales anterior to the dorsal fin is no less than 90 and this number does not include those of the basal fulcra of the dorsal fin. The exposed part of the mid−dorsal scales are cordate, generally wider than long but tend to be narrower toward the dorsal fin with the width/length ratio varying from about 2–2.1 to 0.7–0.75 from the skull to the dorsal fin ( Fig. 9A 1, B 1 , B 2 , D 1 ). The posterior exposed part of each scale overlaps about the anterior one−third of the succeeding scale and bears a plate−like ventral median crista ( Fig. 9B ). The surface of each scale is ornamented with 12 to 20 longitudinal rows of posteriorly directed spine−like tubercles. The exposed parts of the scales just behind the dorsal fin are relatively thick, longer than wide, with blunt spearhead shaped end. These scales tend to increase in size posteriorly. In the anterior part of each scale there is a concaved facet to accept the posterior part of the preceding scale ( Fig. 9A 1, D 1 , D 3).

Different from the Middle Triassic Saurichthys from Monte San Giorgio ( Rieppel 1985) the mid−ventral scale row of Sinosaurichthys longipectoralis begins to develop just behind the skull. This scale row consists of loosely articulated small suboval plates ( Fig. 9A 2 , C) in anterior one−third part between the skull and pelvic fins. The following scales increase in length posteriorly and become lanceolate toward the pelvic fins. Slightly anterior to the pelvic fins, the mid−ventral scale row is branched to form the anal loop. Five pairs of the scales are, at least, involved in the anal loop but the accurate number is not clear due to the preservation. The last scale anterior to the anal loop is elongated, with its posterior part expanded into a rhombic plate to overlap on the first paired scale in the anal loop, which is also very large, as long as four to five times of each of the subsequent anal loop scales, expanding anteriorly and tapering posteriorly with some longitudinal fine grooves on its surface and a hook−like spine in the posterior end ( Fig. 7E, F ). This paired large scale was incorrectly considered by Wu et al. (2008) as a “clasper−like” gonopodium. The mid−ventral scales in the caudal region are lanceolate and similar to the mid−dorsal ones of the same region ( Fig. 9D 3).

The mid−lateral scale row runs through to the end of the body. The scales are roughly triangular to rhombic in outline, differentiated into a narrow dorsal half that is ornamented with some posteriorly directed spine−like tubercles and a wider, smooth ventral half ( Fig. 9E ). The dorsal half is evidently higher and more acute than the ventral half in the scales anterior to the dorsal fin and tends to decrease in height posteriorly and becomes as deep as the ventral half posterior to the dorsal fin. Generally, the length of two mid−lateral scales equals that of one mid−dorsal scale. No lateral line openings are observed in the scales.

The ventrolateral scale row commences a short distance anterior to the pelvic fins and are interrupted by the pelvic fins. The scales are suboval to rhombic ( Fig. 9B 3) and smaller than the mid−lateral scales.

Figures

Fig. 5. Line drawings of saurichthyid fish Sinosaurichthys longipectoralis gen. et sp. nov. from Middle Triassic of Yangjuan Section, Panxian, Guizhou, China. A. GMPKU−P1225. B. GMPKU−P1141. C. Tentative restoration of skull in dorsal view. D. Lower jaw in medial view. E. Posterior part of lower jaw in dorsal view; anterior facing left.

Fig. 6. Line drawings of saurichthyid fish Sinosaurichthys longipectoralis gen. et sp. nov. from Middle Triassic of Yangjuan Section, Panxian, Guizhou, China. A. Posterior part of the skull GMPKU−P1183. B. Skull GMPKU−P1361. C. Skull GMPKU−P1099. D. Restoration of parasphenoid in lateral (D1) and ventral (D2) views. E. Tentative restoration of upper jaw in ventral view, size referred from GMPKU−P1233. F. Isolated left hyomandible in medial view (F1) and ceratohyal (F2) from GMPKU−P1253. Anterior facing right in A, D, F and left in B, C, E.

Fig. 1. Locality map and lithological columns of two sections in Guizhou and Yunnan Provinces, China.

Fig. 2. Illustration showing measurement conventions. A. Body in lateral view. B. Median fin in lateral view. C. Mid−dorsal scales in dorsal view.

Fig. 7. Saurichthyid fish Sinosaurichthys longipectoralis gen. et sp. nov. from Middle Triassic of Yangjuan Section, Panxian, Guizhou, China. A. Line drawings of right posttemporal−supracleithrum form GMPKU−P1253 in dorsal view (A1), right and left cleithrum in lateral (A2), and medial (A3) views, and left and right clavicles in lateral (A4) and medial (A5) views. B. Line drawing of right posttemporal−supracleithrum from GMPKU−P1126 in ventral view. C. Photograph of the micro−ornamentation in the articular facet of the cleithrum for the opercle from GMPKU−P1361. D. Reconstructed left pectoral girdle and pectoral fin, mainly based on GMPKU−P1233 (holotype). E, F. Pelvic girdle and pelvic fins in GMPKU−P1362 (E) and GMPKU−P1211 (F). Anterior facing left in A4, A5, C, F and right in A1–A3, B, D, E.

Fig. 8. Line drawings of saurichthyid fish Sinosaurichthys longipectoralis gen. et sp. nov. from Middle Triassic of Yangjuan Section, Panxian, Guizhou, China. A. Axial skeleton in posterior abdominal region (A1) and neural arches (left) in anterior caudal region (A2) from GMPKU−P1126. B. Isolated neural arch (left) immediately behind skull of GMPKU−P1233 (holotype) in lateral view. C. Isolated neural arch (left) in mid−abdominal region of GMPKU−P1211 in lateral view. D. Paired neural arches in middle part of caudal peduncle of GMPKU−P1089 in ventral view. E. Restoration of right neural arch bearing foramen in medial view. F. Neural arches (right) closely behind skull of GMPKU−P1366 in medial view. Anterior facing left.

Fig. 9. Line drawings of saurichthyid fish Sinosaurichthys longipectoralis gen. et sp. nov. from Middle Triassic of Yangjuan Section, Panxian, Guizhou, China. A. Mid−dorsal scales slightly behind skull of in dorsal view (A1) and an isolated mid−ventral scales behind skull in external view (A2) from GMPKU−P1233 (holotype). B. Mid−dorsal and mid−lateral scales in anterior part of trunk in ventral (internal) view (B1), a single mid−dorsal scale behind skull in ventral view (B2), and ventrolateral scales in lateral view (B3) from GMPKU−P1126. C. An isolated mid−ventral scales behind skull in internal view from GMPKU−P1366.D. Mid−dorsal and mid−lateral scale rows anterior to dorsal fin (D1) and mid−ventral scales anterior to anal fin (D2), and squamation in caudal peduncle region (D3) from GMPKU−P1214. E. Mid−lateral scales in lateral view (E1), mid−lateral scales in anterior part of trunk in medial (E2), and lateral (E3) views from GMPKU−P1211. Anterior facing left in A–D, E1, E2 and right in E3.