Miroscyllium Shirai and Nakaya, 1990

Underwood, Charlie J. & Schlögl, Jan, 2013, Deep-water chondrichthyans from the Early Miocene of the Vienna Basin (Central Paratethys, Slovakia), Acta Palaeontologica Polonica 58 (3), pp. 487-509 : 498-499

Genus Miroscyllium Shirai and Nakaya, 1990

Type species: Centroscyllium sheikoi Dolganov, 1986 ; Recent , Kyushi− Palau Ridge, Pacific .

aff. Miroscyllium sp.

Fig. 7H–K .

1972 Centroscyllium sp. ; Ledoux 1972: fig. 10.

2006 Miroscyllium sp. ; Adnet et al. 2006a: fig. 3 (refiguring of specimens from Ledoux 1972).

Material.—Ten lower partial and near complete teeth including SNM Z 27469 to SNM Z 27472.

Description.—As no upper teeth of this taxon were recovered, the degree of dignathic heterodonty cannot be assessed.

The lower lateral teeth are very small, less than 1.5 mm wide, and show extreme labio−lingual compression, rendering the teeth highly fragile. There is a slender and erect or distally inclined main cusp flanked by (where preserved) one or two pairs of lateral cusplets. The main cusp is at least twice as high as wide and has straight to faintly concave edges, while the lateral cusplets are proportionally lower and wider. The cusps are clearly separated but a continuous cutting edge is present across all cusps. The root is considerably wider than high and rhombic in profile, with the upper edge being distally displaced. On the labial face, enameloid extends over half way to the base of the tooth, and has a convex and weakly pectinate lower edge. There are numerous foramina irregularly spread along, and below, the base of the enameloid. In some teeth there is a fine wrinkled surface texture on the lowermost part of the enameloid. The lingual face of the root is flat and smooth, with a slight shelf at the base of the cusps. There is a foramen at the top of the root below the main cusp, and several smaller foramina along the transverse bulge at the top of the root, some within small pits. In one tooth ( Fig. 7J ) a region of open groove on the lingual root face suggests that the main foramina at the top and bottom of the root are connected. There are vertical notches on the mesial and distal edges of the tooth, with the mesial notch displaced labially and the distal notch displaced lingually.

A lower symphyseal tooth ( Fig. 7H ) is higher than wide. It is in many ways similar to the lateral teeth, but differs in a number of respects. The main cusp is flanked by a single pair of lateral cusplets, and overlies a root that has a concave basal face, giving rise to poorly developed root lobes. At the base of the enameloid on the labial tooth face, a row of foramina is partly merged to form an irregular slot. Foramina are also present at the base of the labial root face and lower part of the lingual root face where they are not present in the lateral teeth. On the lateral parts of the lingual face there are vertical concavities, with the presence of these concavities on both sides of the same root face being indicative of a symmetrically positioned, and thus symphyseal tooth.

Remarks.—These teeth are extremely fragile and the majority are severely damaged. Despite that, there is sufficient material to have a good idea of the overall morphology of the teeth. While the lower lateral teeth are very distinctive, the symphyseal tooth is somewhat similar to the upper anterior teeth of Paraetmopterus horvathi sp. nov. Despite this, it differs in being more labio−lingually compressed and having a deeper root without well defined root lobes in addition to having the vertical concavities that form part of the locking mechanism of lower teeth. The teeth agree very closely with two teeth figured by Ledoux (1972) from the Miocene of France as Centroscyllium sp. These teeth were subsequently placed within Miroscyllium , following a study of the dentition of extant material by Adnet et al. (2006a). While our specimens are similar to the lower teeth of adult Miroscyllium sheikoi , they are more mesio−distally expanded. It is therefore possible that while the species seen here is strongly reminiscent of Miroscyllium , and possibly very closely related to it, it represents a taxon with lesser degrees of ontogenetic heterodonty and rather wider lower teeth.

Figures

Fig. 7. Miocene squaliform sharks Etmopterus and aff. Miroscyllium teeth from Cerová section in Malé Karpaty, Slovakia. A–G. Etmopterus sp. A. SNM Z 27463, bed 17–18, lower tooth in labial (A1) and lingual (A2) views. B. SNM Z 27464, bed 17–18, lower tooth in labial (B1) and lingual (B2) views. C. SNM Z 27465, bed 17–18, lower posterior tooth in labial (C1) and lingual (C2) views. D. SNM Z 27465, bed 21–22, lower tooth in labial (A1) and lingual (A2) views. E. SNM Z 27466, bed 17–18, lower tooth in labial (E1) and lingual (E2) views. F. SNM Z 27467, bed 17–18, lower tooth in labial view. G. SNM Z 27468, bed 8–9, upper tooth in labial (G1) and lingual (G2) views. H–K. aff. Miroscyllium sp. H. SNM Z 27469, bed 17–18, lower symphyseal tooth in labial (H1) and lingual (H2) views. I. SNM Z 27470, bed 17–18, lower tooth in labial (I1) and lingual (I2) views. J. SNM Z 27471, bed 21–22, lower lateral tooth in labial (J1) and lingual (J2) views. K. SNM Z 27472, bed 17–18, lower tooth in labial (K1) and lingual (K2) views.