Sinosaurichthys minuta, 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-685D-075B-FCE2-8DB593F5326F |
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treatment provided by |
Felipe |
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scientific name |
Sinosaurichthys minuta |
| status |
sp. nov. |
Sinosaurichthys minuta sp. nov.
Figs. 17–20 View Fig View Fig View Fig View Fig .
Etymology: From Latin minutus, small, referring to the small size of the new species.
Type material: Holotype GMPKU−P1955 , a laterally compressed, complete skeleton . Paratypes: GMPKU−P1928 , 1369 , 1370 and 1372 .
Type locality: Dawazi , Luoping, Yunnan Province, China .
Type horizon: Lower part of the fossiliferous strata near the top of the Third Member of the Gejiu Formation (Pelsonian of Anisian, Middle Triassic).
Referred specimens.—GMPKU−P1382, 1390, 1929, 1931, 1932, 1933, 1936, 1938, and 1948. Most of them are complete skeletons.
Diagnosis.—Small−sized Sinosaurichthys with standard body length of adults no more than 210 mm; low triangular−shaped dorsal and anal fins with relatively numerous segments in fin rays; fewer neural arches between opercle and caudal fin (154–156) and those bearing neural spines (126–127), fewer distinct haemal spines in caudal region (10–11), and fewer mid−dorsal scales in front of dorsal fin (62–63) than those in the other species of Sinosaurichthys ; cleithrum plate lowest (depth/length ratio approximately1) among three species of Sinosaurichthys . Fin formula: P 14–16, V 18–20, D/A 40–42/ 40–42, C 34–38/34–37.
doi:10.4202/app.2010.0007
Description
General appearance.—The body is long and slender ( Fig. 17A, B View Fig 1 View Fig , C), with a standard body length varying between 100–210 mm. The skull length is about 33–37% of the standard body length and the rostrum makes up about 60–63.5% of the skull length and about 68.7–72.7% of the mandible length ( Table 1). The pectoral fins lie above the midline of the body, close behind 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 ( Table 2).
Snout.—The rostrum is also rather long and slender and the dermal bones are almost arranged in the same pattern with the other two species of Sinosaurichthys ( Figs. 17A, B View Fig 1 View Fig , C, 18 View Fig , 19A View Fig 1, B 1 View Fig ). The only difference from the type species is the anterior part of the nasalo−antorbital is mainly decorated with tubercles rather than striation.
Dermal skull roof.—The composition of the dermal skull roof of S. minuta is almost the same as that of S. longimedialis , wider in proportion to skull depth than that of S. longipectoralis ( Fig. 19A View Fig 1, B 1 View Fig ). The paired extrascapular is also relatively large in proportion to the skull roof width, and is of a rounded triangular shape, almost completely separates the posttemporal−supracleithrum from the dermopterotic, and in direct contact with the first mid−dorsal scale posteromedially ( Figs. 18B, C View Fig , 19C View Fig ).
Cheek and opercular series.—The orbit and the dermal cheek bones are highly consistent with those in S. longimedialis in shape and arrangement ( Figs. 17–19B View Fig View Fig View Fig 1 View Fig ) and nothing can be added besides the infraorbitals, which clearly 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. 18C View Fig , 19B View Fig 1 View Fig ).
The opercular apparatus consists of a single large semicircular opercle with the depth/width ratio varing from 1.43 to 1.8 (average 1.64) ( Table 2). The surface of the opercle is doi:10.4202/app.2010.0007
ornamented mainly with fine and dense concentric lines and tubercles. As in the other two species of Sinosaurichthys , the gular and branchiostegal rays are absent.
Mandible.—The shape and pattern of dermal bones in the lateral side of the mandible is almost the same with that of the two species described above ( Fig. 18 View Fig ).
Palate.—Because of the preservation only part of the parasphenoid can partially been seen, similar to the situation in S. longimedialis . This includes the long anterior stem across the ventral part of the orbit, a posteriorly forked posterior stem between the dermopterotic and opercle, and a large paired ascending process posterior to the orbit ( Figs. 18A, B View Fig , 19A View Fig 1 View Fig ), but suggestive for the same morphology and construction to that in the type species of the genus.
Hyoid arches.—The hyomandible is more or less hockeystick shaped ( Fig. 19A View Fig 1 View Fig ), with a horizontally extended dorsal portion and a posteroventrally inclined ventral portion, slightly different from that in the type species in shape.
Dentition.—The teeth along the labial edge of both jaws are arranged in the same way and shape as in the other species of Sinosaurichthys ( Fig. 17B View Fig 2 View Fig ). The large teeth are quite small and some of them curved posteriorly, similar to those in S. longimedialis ( Fig. 17B View Fig 2 View Fig ).
Paired fins and girdles.—The pectoral fin is roughly triangle−shaped, consisting of 14–16 unsegmented fin rays. The length of the pectoral fin varies from slightly less than to more than the skull depth ( Table 2), much shorter than that of the type species of the genus.
No radials or endoskeletal elements of the pectoral girdle can be discerned, but the dermal pectoral girdle is well preserved in most of the specimens and its elements are consistent with those in S. longimedialis in shape and configuration ( Figs. 18 View Fig , 19A View Fig 1, B 1 View Fig , B 2 View Fig ).
The pelvic fins are relatively small and triangular in shape ( Fig. 20C View Fig ), each consisting of about 18–20 unsegmented fin rays. Little 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 other species of Sinosaurichthys . They are triangular−shaped, much lower than those in the two species described above, with the depth almost equal to width ( Fig. 20A View Fig 2 View Fig ). The dorsal fin consists of about 41–50 and the anal fin of 42–48 fin rays, with a maximal segmentation of three to four times in the dorsal and four times in the anal fin.
Only the anterior radials of the dorsal and anal fins are ossified, eight and seven to ten radials can be distinguished in the dorsal and anal fin respectively.
The caudal fin is deeply forked, generally with 35–38 fin rays in each lobe ( Figs. 17A, B View Fig 1 View Fig , C, 20A View Fig 1 View Fig , Table 2). The fin rays are generally segmented three to four times proximally, occasionally five times, and branched distally once or twice.
In the holotype, two basal fulcra are seen at the origin of the dorsal fin and three of the anal fin. The fringing fulcra, as in S. longimedialis , are present in all unpaired fins, consisting of small spine−like elements overlapping one by one in the distal part of the leading edge of the marginal fin rays.
Axial skeleton.—The axial skeleton consists of the neural and haemal arches similar in structure to those in the other species of Sinosaurichthys . The neural arches between the opercle and caudal fin number about 154–156 and the anterior 126–127 ones bear distinct neural spines, slightly fewer than that in S. longimedialis . In the caudal fin region, there are about 13–14 neural arches supporting the fin rays of the epichordal lobe of the caudal fin. Distinct haemal spines are developed in the initial 10 to 11 haemal arches in the caudal region, the fewest among the three species of the genus.
Squamation.—Similar to the two species described above, Sinosaurichthys minuta also bears six longitudinal scale rows.
There are 62–63 mid−dorsal scales in front of the dorsal fin. These scales are also cordate in the posterior exposed portion ( Fig. 20B, E View Fig 1 View Fig , E 2 View Fig ), wider than those in the type species and narrower than in S. longimedialis , with the width/length ratio about 2.1–2.3 near the skull and 1–1.5 near the dorsal fin, and are decorated with spine−like tubercles ( Fig. 20B View Fig ).
The mid−ventral scale row divides into two rows slightly anterior to the pelvic fins to form the anal loop and each branch consists of four scales ( Figs. 19A View Fig 2 View Fig , 20A View Fig 2 View Fig , C). 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 of paired scales of the anal loop is also elongated, expanding anteriorly and tapering posteriorly. In the caudal peduncle, the mid−ventral scales are similar with the mid−dorsal ones in both shape and ornamentation, bearing some strong posteriorly pointed tubercles ( Fig. 20D View Fig ).
The mid−lateral scales have a similar shape to that of type species and the dorsal part of the external surface is decorated with a few posteriorly−directed spines ( Fig. 20E View Fig 3).
The ventrolateral scale row commences a short distance posterior to the skull and generally consists of small semicircular to rhombic scales, decorated with a few posteriorly pointed tubercles, and the scales are evidently enlarged near the origin of the pelvic fins ( Fig. 19A View Fig 2 View Fig ). Posterior to the pelvic fins, the scale row continues backwards to the caudal fin ( Fig. 20A View Fig 1 View Fig ).
Remarks.— S. minuta is very similar to S. longimedialis in the general morphology. The lack of substantial differences between the two species, except for the body size and the shape of the unpaired fins, makes it easy to regard S. minuta as the juvenile of S. longimedialis . However, the degree of the segmentation in the unpaired fins between the two species does not support the juvenile−adult relationship because the number of the segments of the fin rays usually increases accompanying with the growth of fin rays during ontogeny. It would be contradictory that the segmentation of the fin rays is fewer in adults than in juveniles. The number of rays in the pectoral fin and ossified haemal spines in the caudal region is also different between the two species. Thus, here we treat S. minuta as a separate species from S. longimedialis . Additionally, the two species occur in different stratigraphic levels. Field excavation doi:10.4202/app.2010.0007
reveals that S. longimedialis is restricted to the upper part of the fossiliferous strata, about 3–5 m above the level containing S. minuta in the Dawazi Section.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.