Silurus spinosus, Kovalchuk & Ferraris, 2016

Kovalchuk, Oleksandr & Ferraris, Carl J., 2016, Late Cenozoic catfishes of Southeastern Europe with inference to their taxonomy and palaeogeography, Palaeontologia Electronica 51 (9), pp. 1-17 : 3-7

Genus SILURUS Linnaeus, 1758 † Silurus spinosus n. sp.

Figure 3.1 -13

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Etymology. The name refers to the unusual multiserial denticulations on the pectoral-fin spine.

Type material. Holotype NMNHU-P 29 /1747, complete left pectoral-fin spine ( Figure 3.1-5 ) . Paratypes NMNHU-P 29 /1748, 1749, 1750 right pectoral-fin spines, 29/1756 parasphenoid, 29/ 1906 praemaxilla, 29/1911 quadrate, 29/4002 right dentary, 29/1852 articular, and 29/1814 cleithrum .

Additional material. 5 praemaxillae, 1 articular, 5 quadrates, 30 dentaries, 9 cleithra, 72 proximal and 42 distal portions of pectoral-fin spines ( NMNHU-P 29/1751-1755, 1757-1813, 1815-1851, 1853-1905, 1907-1910, 1912-1917, Popovo 3); 8 dentaries, 17 proximal and 13 distal portions of pectoral-fin spines ( NMNHU-P 29/3997-4001, 4003-4035, Lobkovo); and 6 proximal portions of pectoral-fin spines ( NMNHU-P 638-643, Mykhailivka 2).

Type locality. Popovo 3, near Vasylivka, Zaporizhzhia region, Southern Ukraine ( Figure 1 ) .

Geological age and distribution. late Miocene, late Sarmatian of Southeastern Europe.

Diagnosis. Silurus spinosus n. sp. differs from other species of the genus Silurus in the following unique combination of characters: (1) multiserial denticulations at the lateral margin of pectoral-fin spine shaft; (2) projecting flattened crests on the ventral surface of medial part of the parasphenoid; (3) rounded and shortened facies articularis quadrati on the articular; and (4) narrow oral surface of the dentary with 3-5 tooth rows, weakly developed dental shelf and widened symphysis.

Description. Pectoral-fin spine ( Figure 3.1 -7) is extended in length and tapered to a point at the distal end. The surface of the bone has distinct longitudinal grooves. The shaft is lenticular or rounded in cross-section, with a deep furrow on the anterior plane, starting from the base and continuing to the tip. The base of the pectoral-fin spine is moderately widened and slightly flattened (arched in some specimens), deflected medially from the shaft. There are usually 3, rarely 4-5, rows of weak denticulations. The denticulations extend basally to the level of approximately 1/5 of the shaft length and point in different directions. The medial margin of the shaft has strong, pointed, conical and slightly curved denticulations. The ratio of width to length is near 1:4-1:5. The dorsal process of the spine base ( Figure 3.5 ) has a swollen margin, the ventral process is fairly wide and lobate, and the anterior process is small and rounded. The longest spine examined was 45.2 mm (holotype 37.0 mm). The parasphenoid ( Figure 3.8 ) is an arched bone, compressed dorsoventrally, with two flattened crests projecting on the ventral surface. The posterior part of the parasphenoid is widened caudally and the carotid grooves are high and wide. The dentary ( Figure 3.9 ) is characterized by a narrow oral surface (only 3-5 tooth rows), weakly developed dental shelf and widened symphysis. Dentary teeth are small, with conical crowns and circular bases. The praemaxilla ( Figure 3.12 ) is flattened, elongated and contains numerous rows of small teeth. The cleithrum has a deep cavity for the articular head of the pectoral-fin spine ( Figure 3.10 ) that is uniform in width and medially curved in a smooth arc. The articular facet (facies articularis quadrati) on the articular bone ( Figure 3.11 ) is wide anteriorly and narrow posteriorly. The bone wall is high (45°), with a wide ventroposterior angle. The quadrate ( Figure 3.13 ) is robust; its articular facet is nearly rectangular, with smoothly rounded edges.

Remarks. The various disarticulated bones that comprise the paratype series and additional material were assigned to † Silurus spinosus n.sp. based on their clear differences from the comparable elements of the only other catfishes ( Silurus soldatovi , Silurus sp. ) currently known from the outcrop. Differences in those elements are not emphasized in the systematic discussion, below, inasmuch as the pectoral-fin spine differences are sufficient to establish the species as new and the associated bones are necessarily only hypothesized to be those of † S. spinosus .

Systematic discussion. The only other named extinct species of catfish that is currently assigned to Silurus is Silurus joergi Gaudant, 2015 , from the Miocene strata of Höwenegg ( Germany). The pectoral-fin spine of Silurus joergi is comparably shorter, much more robust and clearly rounded in cross-section. There are short blunt denticulations on the medial margin, which are slightly shifted in lateral projection ( Gaudant, 2015).

Of the extant species of the genus. † Silurus spinosus n.sp. is most similar in morphology to Silurus soldatovi Nikolsky and Soin, 1948 , and Silurus cochinchinensis Valenciennes, 1839 , in curvature of the pectoral-fin spine. However, the spine of S. soldatovi has only numerous uniserial small weak denticulations on the medial and lateral margins, and the spine of S. cochinchinensis has a deep notch at the base and characterized by the presence of large flattened accrete denticulations only on the medial margin of the shaft, which becomes very thin ( Kobayakawa, 1989). The pectoral-fin spine of the new species is significantly narrower distally and is characterized by a less swollen dorsal process and less regular uniserial denticulations on both margins of the shaft than that of Silurus aristotelis ( Agassiz, 1856) , ( Kobayakawa, 1989). The pectoral-fin spine of Silurus biwaensis ( Tomoda, 1961) , in addition to features mentioned above, is comparably narrower ( Kobayakawa, 1989). Other species of the genus Silurus are even less similar to † Silurus spinosus n. sp. For example, pectoral-fin spine of Silurus glanis Linnaeus, 1758 has more robust articular processes and yielded long accrete denticulations on the medial margin; at the same time there are no any denticulations at the lateral margin of the shaft. The pectoral-fin spine of Silurus grahami Regan, 1907 has a wider base and ventral process, a naked medial margin and small weak uniserial denticulations on the lateral margin ( Kobayakawa, 1989). Such denticulations are completely absent on the pectoral-fin of Silurus microdorsalis ( Mori, 1936) , with the exception of a few of them at the top of the shaft ( Kobayakawa, 1989).

Figures

FIGURE 1. Investigated localities with late Miocene, Pliocene and Pleistocene catfish remains. 1, Popovo. 2, Mykhailivka. 3, Lobkovo. 4, Frunzovka. 5, Palievo. 6, Otradovo. 7, Lysa Gora. 8, Kubanka. 9, Novoelizavetovka. 10, Cherevichne. 11, Vasylivka. 12, Verkhnya Krynitsya. 13, Egorovka. 14, Novoukrainka. 15, Pontian lectostratotype. 16, Vinogradovka. 17, Nerubaiske. 18, Trudomirovka. 19, Novopetrovka. 20, Kamenskoe. 21, Kotlovina. 22, Shkodova Gora. 23, Shirokino. 24, Obukhovka. 25, Novokyivka. 26, Semibalka.

FIGURE 3. Isolated bones assigned to †Silurus spinosus n. sp. 1-5, holotype, left pectoral-fin spine (NMNHU-P 29/ 1747, Popovo 3): dorsal view (1), ventral view (2), medial view (3), lateral view (4), proximal articulation surface (5). 6- 7, distal fragments of pectoral-fin spines (NMNHU-P 29/4034-4035, Lobkovo). 8, medial part of parasphenoid (NMNHU-P 29/1756, Popovo 3), dorsal view. 9, right dentary (NMNHU-P 29/4002, Lobkovo), medial view. 10, symphysal fragment of cleithrum (NMNHU-P 29/1814, Popovo 3), lateral view. 11, articular (NMNHU-P 29/1852, Popovo 3), lateral view. 12, praemaxilla (NMNHU-P 29/1906, Popovo 3), ventral view. 13, articular facet of quadrate (NMNHU-P 29/1911, Popovo 3), anterior view. Scale bars equal 10 mm.