Sinosaurichthys longimedialis, Feixiang & Yuanlin & Guanghui & Weicheng & Dayong & Zuoyu, 2011
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publication ID |
https://doi.org/ 10.4202/app.2010.0007 |
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persistent identifier |
https://treatment.plazi.org/id/3343878F-6844-0751-FCB7-8CC2917C3788 |
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treatment provided by |
Felipe |
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scientific name |
Sinosaurichthys longimedialis |
| status |
sp. nov. |
Sinosaurichthys longimedialis sp. nov.
Figs. 10–16 View Fig View Fig View Fig View Fig View Fig View Fig .
Etymology: From Latin longus and medialis, referring to its exceptionally elongated median fins.
Type material: Holotype GMPKU−P1927 , a laterally compressed, almost complete skeleton . Paratypes: GMPKU−P1543 , P1936, 1949, 1954.
Type locality: Dawazi , Luoping, Yunnan Province, China .
Type horizon: Upper part of the fossiliferous strata near the top of the Third Member of the Gejiu Formation (Pelsonian of Anisian, Middle Triassic).
Referred specimens.—GMPKU−P1367, 1380, 1388, 1586, 1769, 1935, 1936, 1939, and 1958. Most of them are complete skeletons.
Diagnosis.—Medium−sized Sinosaurichthys (standard body length ranging from 270–470 mm) with unusually elongated median fins with relatively few segments of fin rays; less number of neural arches between opercle and caudal fin (approxi−
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mately 157–172), less number of anterior ones with neural spines (130–146); and less number of mid−dorsal scales in front of dorsal fin (69–86) than in type species; 14–15 distinct haemal spines in caudal region; pectoral fin triangular shaped with length about 1/3 of mandible length (shared with S. minuta described below); posttemporal−supracleithrum from either side separated from each other by anterior mid−dorsal scales (shared with S. minuta described below); cleithrum plate (depth/length ratio ca. 1.2–1.25) much lower than in type species (approximately 1.8), but close to that in S. minuta (approximately 1). Fin formula: P 18–19, V 18–20, D/A 44–49/>40–48, C 37–39/37–39.
Description
General appearance.—The body of Sinosaurichthys longimedialis is long and slender ( Fig. 14 View Fig ), with a standard body length in adult varying from 270–470 mm. The skull occupies about 22–30% of the standard body length. It is worthy to note that the specimens attributed to this species can be divided into two distinct morphological types that one is characterized with relatively long rostrum (60–66% of the skull length or more than 70% of the mandible length) and fewer neural arches between the opercle and the caudal fin (approximately 157–158 with the anterior 131–131 bearing distinct neural spines) and mid−dorsal scales in front of the dorsal fin (approximately 70) ( Fig. 10 View Fig ); and the other is featured by relatively short rostrum (less than 57% of skull length or 66% of the mandible length) and more neural arches between the opercle and the caudal fin (approximately 167–172 with the anterior 141–146 bearing distinct neural spines) and mid−dorsal scales in front of the dorsal fin (>80) ( Fig. 11A View Fig ). These differences probably reflect doi:10.4202/app.2010.0007
sexual dimorphism. We tentatively attribute the former as male and the latter as female based on the specimen abundance between the two morphotypes (approximately 5–6: 1) and the existence of possible breeding tubercles in the pectoral fins in a specimen (GMPKU−P1380, presumed as male; Fig. 13A View Fig ). The pectoral fin inserts high on the flank, but somewhat lower than in the type species, lying close behind the upper portion of the opercle. The pelvic fins are placed nearer to the caudal fin than to the opercle. The dorsal and anal fins are symmetrically arranged, much closer to the pelvic fins than to the caudal fin ( Figs. 10 View Fig , 11 View Fig ; Table 2). The median fins are considerably elongated, generally longer than the mandible length.
Endocranium.—Similar to the type species, only part of the orbitotemporal region can be seen ( Fig. 12C View Fig ) and nothing can be added besides the foramina possibly related to the oculomotor nerve.
Snout.—The snout of the presumed female is shorter in proportion to skull length ( Fig. 14 View Fig ) than that of the presumed male ( Figs. 12A View Fig , 13B View Fig ). The nasalo−antorbital probably has more portions involved in the skull roof. The dermal bones of the snout are, on the whole, arranged in the same pattern as in the type species ( Figs. 12–14 View Fig View Fig View Fig ). The only difference from the type species is that the anterior part of the nasalo−antorbital is mainly decorated with tubercles rather than striations.
Dermal skull roof.—The skull roof may be rather wide in proportion to the skull depth judged from the width of the mid−dorsal scales immediately behind the skull, possibly the widest among the species of Sinosaurichthys . The general shape and arrangement of the dermal bones in the skull roof are similar to that in the type species. The extrascapular is rounded triangular and it is so large that it almost separates the posttemporal−supracleithrum from the dermopterotic, and directly overlaps on the first mid−dorsal scale posteromedially doi:10.4202/app.2010.0007
( Fig. 13A, C View Fig ). Three openings of the temporal commissure of the sensory canal can be seen in the ventral surface of the extrascapular in GMPKU−P1945 ( Fig. 12B View Fig ).
Cheek and opercular series.—The orbit is elliptical to circular, slightly smaller than that of the type species in proportion to the skull depth, confined by the nasalo−antorbital anteriorly and by the frontal dorsally. The dermosphenotic is small and crescent shaped, occupying the posterodorsal corner of the orbit between the frontal and dermopterotic. The infraorbitals consist of three elements: the anteriormost one (lacrimal) is lanceolate, forming the anteroventral rim of the orbit ventral to the nasalo−antorbital; the other two compose the posterior rim of the orbit ( Figs. 13B View Fig , 14C View Fig ).
The postorbital lobe of the maxilla is rather high with a truncated rather than a convex dorsal margin that is almost fully covered by the dorsal portion of the preopercle ( Figs. 12–14 View Fig View Fig View Fig ), different from that in the type species, but similar to that in S. minuta described below.
Similar to the type species, the opercular series consists of a single large semicircular opercle ( Figs. 12–14 View Fig View Fig View Fig ), with the depth/width ratio varying from 1.55 to 1.82 (average 1.67) ( Table 2). The gular and branchiostegal rays are absent.
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Mandible.—The shape and arrangement of dermal bones in the lateral side of the mandible is almost the same as in the type species ( Figs. 12–14 View Fig View Fig View Fig ). However, the ventral margin in the specimens of the presumed female seems to be more convex than in these of the presumed males ( Fig. 14 View Fig ).
Palate.—No information about the vomers is available due to the preservation. The parasphenoid is only partially exposed in the current materials. The parasphenoid passes across the orbit in a similar way as in the type species with paired large ascending processes posterior to the orbit and the foramina of both the efferent pseudobranchial and the common carotid arteries penetrating the parasphenoid in the same positions as in the type species ( Fig. 12C View Fig ). The posterior stem of the parasphenoid also extends posteriorly under the occipital region, beyond the anterior margin of the opercle with a distinct notch in the posterior tip ( Fig. View Fig
12C). Hyoid arches.—Only the ceratohyal is preserved ( Fig. 12B View Fig ).
In GMPKU−P1388 , it has a shape similar to that in the type species .
Dentition.—Teeth along the labial edge of both jaws are arranged in the same way as in the type species, one row of large teeth intercalated with several small ones ( Figs. 10A View Fig 2 View Fig , 11B View Fig 2 View Fig ). The apical tip of most large teeth bends posteriorly, differing from that in the type species.
Paired fins and girdles.—The pectoral fin is of typical triangular shape consisting of 19 unsegmented fin rays in the holotype ( Figs. 10A View Fig 1 View Fig , 12A View Fig , 15A View Fig 1 View Fig ). The 6 th is the longest. The length of the pectoral fin varies from less than to more than the skull depth ( Table 2). The fin rays begin to branch distally from the 10 th one. In GMPKU−P1380, many small tubercles are present on the surface of the distal part in the pectoral fin rays ( Fig. 13A View Fig ), a feature probably related to breeding (nuptial) behavior of adult male individuals.
Little information of radials can be added whereas the scapulocoracoid can be partially seen in some specimens with a large foramen in the anterodorsal part behind the dorsal stem of the cleithrum ( Figs. 13A View Fig , 14A View Fig ).
The dermal pectoral girdle is well preserved in most of the specimens. The posttemporal−supracleithrum, as in the type species, consists of a dorsal and a ventrolateral portion ( Figs. 13A View Fig , 14A, B View Fig ), but the dorsal portion of this bone is separated from its opposite pair by the mid−dorsal scales and the ventrolateral portion is deeper ( Figs. 13A View Fig , 14A, B View Fig ). Anteriorly, this bone bears a subcircular articular facet for the extrascapular and posteriorly an articular facet for the mid−lateral scale between its two portions. Although the cleithrum is also boot−shaped, the rectangular posterior blade of this bone is less deep (approximately 1/3 of the skull depth) than in the type species and the dorsal stem is vertically oriented rather than anterodorsally inclined ( Fig. 14A View Fig ). The clavicle is subovate to round triangular, and articulates posteriorly to the cleithrum ( Figs. 12B View Fig , 13B View Fig , 14C View Fig ). In addition, a small triangular shaped bone can be observed in some specimens attached to the lateral side of the posterior process of the dermopterotic and anterior to the posttemporal−supracleithrum, with ornamentation similar to that on areas of other dermal bones of the pectoral girdle covered by the opercle, possibly suggesting a presupracleithrum.
The pelvic fin is relatively small and triangle−shaped, consisting of 18–22 unsegmented but distally branched fin row in anterior (D 3) and middle parts of abdominal region (D 4); mid−ventral and ventrolateral scale rows anterior to pelvic fins (D 5). E. Idealized mid−dorsal scale row (dorsal view) near skull (E 1) and in front of dorsal fin (E 2), left mid−lateral scale row in abdominal region in lateral view (E 3), and left ventrolateral scale row in posteroventral abdominal region (E 4). Restoration mainly based on holotype GMPKU−P1543. Anterior facing right in B, C and left in A, D–I.
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rays. No information about the pelvic bone is available in the current materials.
Unpaired fins.—The dorsal and anal fins are arranged in the same way as in the type species. The dorsal fin consists of about 44–49 and the anal fin of 47–48 fin rays, which are segmented proximally two to three times. In the holotype (GMPKU−P1927) the anterior 17 fin rays of the dorsal fin are unbranched and the rest are branched once distally, with the 14–16 th fin rays longest. Both the dorsal and anal fins show considerable elongation to different extents that make the fins quite flexible in their distal part. The length of the fins varies from about half of to even more than the mandible length in different specimens ( Figs. 10 View Fig , 11 View Fig , 15A View Fig 2 View Fig , B; Table 3). The elongation of the median fins is unique to this species. In some large specimens, a total of 15 and 16 elongated axonosts can be seen in the dorsal and anal fins, respectively. In other smaller specimens only parts of them are ossified.
The caudal fin is deeply forked, and its lobes are extremely elongated, longer than the mandible length ( Figs. 10 View Fig , 11 View Fig , 15A View Fig 2 View Fig , B). Each lobe consists of 37–39 fin rays, with three to four and three to six segments in the epi− and hypochordal lobes, respectively, and bifurcate once to twice distally.
The basal and fringe fulcra are developed in all median fins. There are 3–4 and 5 basal fulcra in the dorsal and anal fin, respectively, and 2–3 in each lobe of the caudal fin. The fringing fulcra are distally developed on the surface of the margin leading fin rays of the median fins, consisting of small spin−like plates overlapping one by one ( Fig. 15A View Fig 3).
Axial skeleton.—The neural and haemal arches are similar to those in the type species in structure and morphology ( Fig. 16A). The total number of the neural arches in front of the caudal fin is about 157–158 in the presumed male individuals and about 167–172 in the presumed female ones, both are less than that in the type species. The neural spines are developed in the anterior 131–132 and 141–146 ones in the two presumed sexual morphotypes, respectively. In the caudal fin region, the neural arches continue to the tip of the fin to support the fin rays of the epichordal lobe.
The haemal arches between the pelvic and anal fin are similar to those of the type species, consisting of two kinds of alternatively arranged bony plates, one with a distinct haemal spine and the other without. They represent the basi− and inter−ventral arcualia elements, respectively ( Fig. 16A). However, the ossifications of the interventrals are much larger in proportion to those of the basidorsals than in the type species. There are 14–15 distinct haemal spines in the caudal region.
Squamation.—Similar to the type species of the genus, Sinosaurichthys longimedialis also bears six longitudinal rows of scales.
The mid−dorsal scale row runs through the body length, only interrupted by the dorsal fin, generally consisting of 67–70 scales in the presumed male and 86 in the presumed female individuals. The mid−dorsal scales are also cordate in shape, with the width/length ratio of the exposed portion reaching about 2–2.9 near the skull and decreasing gradually toward the dorsal fin to about 1–1.33 ( Fig. 16B, C 1 View Fig , C 2 View Fig , D 1 View Fig , D 2 View Fig , E 1 View Fig , E 2 View Fig ). The exposed portion of the scales is fully covered with posteriorly−directed spines ( Fig. 16B 1 View Fig , D).
Similar to the type species, the mid−ventral scale row begins just behind the skull. The anterior scales are small, subovate, and tend to be larger posteriorly ( Fig. 16D 3 –D 5 View Fig ). A distinct feature of the mid−ventral scales of S. longimedialis is that each scale has a remarkable root that looks like a spiny structure ( Fig. 16D 4, D 5 View Fig ). The scale row divides into two rows slightly anterior to the pelvic fins to form the anal loop. As in the type species, the last scale anterior to the anal loop is enlarged and elongated with a rhombic posterior portion and the first paired scales of the anal loop is also elongated, expanding anteriorly and tapering posteriorly. The exact number of scales forming the anal loop is not clear due to the preservation.
The mid−lateral scales have similar shape with those of the type species and the external surface of the dorsal part is ornamented by posteriorly directed spines ( Fig. 16C 3, D 1 View Fig , E 3).
The ventrolateral scale row begins to develop from the level some distance anterior to the pelvic fins, generally as small rounded triangular or rhombic scales. Their external surfaces are decorated by one to three rows of posteriorly curved spines. The last two to three scales anterior to the pelvic fins tend to be enlarged, and heart−shaped as the basal fulcra. Posterior to the pelvic fin the scale row continues to the caudal fin.
In addition to the scale rows mentioned above, many less ossified small scales, each less than 0.5 mm wide, are scattered between the scale rows ( Fig. 16B 3), similar to the condition in all other saurichthyids described in the current paper.
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