Squaliolus cf. schaubi ( Casier, 1958 )

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 : 492-494

Squaliolus cf. schaubi ( Casier, 1958)

Fig. 5 .

1958 Centroscymnus schaubi Casier ; Casier 1958: pl. 1: 11.

1972 Squaliolus schaubi Casier, 1958 ; Ledoux 1972: fig. 11b, c, f, h–l.

2004 Squaliolus schaubi Casier, 1958 ; Underwood and Mitchell 2004: pl. 1: 3–8.

2006? Squaliolus sp. ; Takakuwa 2006: fig. 4.6.

2011 Squaliolus schaubi ( Casier, 1958) ; Vialle et al. 2011: fig. 2.6.

Material.—137 lower and 89 upper partial and complete teeth including SNM Z 27443 to SNM Z 27454.

Description.—There is extreme dignathic heterodonty with slender and pointed upper teeth and blade−like lower teeth.

The lower teeth are small, being less than 2 mm high. They show very little monognathic heterodonty, with the exception of the rather wide posterior tooth. There is strong labio−lingual compression of the teeth and a well developed cutting edge is present on the cusp and distal heel. There is a single cusp that is strongly inclined distally and comprises less than a quarter of the total height of the tooth. The cusp reaches almost to the distal edge of the tooth, and has weakly convex mesial and distal cutting edges that lack serrations. Rare specimens have a slightly sigmoidal curvature to the mesial cutting edge. Distally, the cusp overhangs a low and rounded distal heel. The tooth below the cusp is roughly rectangular and higher than wide, with a slightly convex distal edge and concave mesial edge. There is a weak notch on the basal edge of the tooth. The labial tooth face is largely covered by enameloid, which reaches at least three quarters of the way to the base of the tooth. There is a major concavity on the mesial side of the tooth that reaches as far distally as level with the middle of the base of the cusp. This lacks enameloid and has a semicircular upper edge. Several small foramina are present along the edge of this concavity. A very well developed foramen is present at the base of the enameloid, creating a narrow ridge between this hole and the mesial concavity. One of two smaller foramina is present behind the main foramen along the weakly curved enameloid base. The lingual side of the tooth is largely flat, but tapers occlusally and basally from a slight horizontal ridge on the upper part of the tooth. There is a deeply indented region below the distal heel, which is the surface that would articulate with the mesial indentation on the labial face of the adjacent tooth. The basal edge of the enameloid is gently curved with a mahttp://dx.doi.org/10.4202/app.2011.0101

jor foramen just below the basal edge of the enameloid at its lowermost point. No other foramina are evident on the lingual tooth face. The posterior tooth is similar to the other lower teeth, but the distal portion of the tooth is highly expanded, with the distal heel forming a long, horizontal blade below which the root is similarly expanded.

The upper teeth are slender and typically between 1 and 1.5 mm high and show a low degree of heterodonty, largely seen as increasing asymmetry of the teeth with distal inclination of the cusp in teeth from more posterior jaw positions. Teeth are higher than wide and comprise a single cusp above a clearly bilobed root. The cusp has straight to slightly concave mesial and distal edges and comprises about half of the height of the tooth. There is a continuous but weak cutting edge separating weakly convex labial and lingual faces. A poorly developed projection is present on the mesial and distal edges of most teeth and forms a slight overhang of the root. At the base of the labial side of the cusp are a pair of weak vertical ridges that pass downwards into sharp−edged extensions of the crown on the labial faces of the root lobes, reaching at least half the height of the root. The root is quite robust and comprises two very well differentiated root lobes forming an internal angle of 9 0° or less. In lateral teeth, the mesial root lobe is longer and has a more rounded termination than the distal lobe. The basal face of the root is flat, but there is not the strongly demarked edge between the basal and labial faces as seen in some squaliform teeth. There is a very large foramen at the base of the crown between the two crown lobes on the labial side, and a small foramen at the sharply angled lingual projection at the top of the root. One or more small lateral foramina may also be present.

Remarks.—While morphologically very similar to specimens from elsewhere referred to Squaliolus schaubi , the teeth recorded here are consistently smaller. It is unclear whether this size difference arises from intraspecific regional variation, as recorded in extant Etmopterus (see Yano 1997) and the Cretaceous squaliform Protosqualus (see Underwood and Mitchell 1999), or if separate but dentally similar taxa are represented. The presence of teeth with a slightly sigmoidal cusp, a character seen in mature males ( Herman et al. 1989), suggests that the teeth are not from juveniles. Specimens of lower teeth with a rather more elongate cusp with more strongly sigmoidal leading edge have been recognized in the Miocene of Germany ( Barthelt et al. 1991, as Squaliolus sp. 1 ) and southern France ( Ledoux 1972: fig. 11a, d, e, g). Lower teeth of this morphology were not recorded during this study and therefore may not be conspecific with Squaliolus schaubi and may instead represent a species of Euprotomicrus Gill, 1862 (see Herman et al. 1989). Two lower teeth figured from the Miocene of Japan by Takakuwa (2006) may represent different species; while the specimen in their fig. 4 may be referable to Squaliolus schaubi , the specimen in fig. 3 differs from S. schaubi in having a higher and more erect cusp, higher tooth shape overall and larger labial foramina.

Figures

Fig. 5. Miocene squaliform shark Squaliolus cf. schaubi (Casier, 1958) teeth from Cerová section in Malé Karpaty, Slovakia. A. SNM Z 27443, bed 20–21, lower tooth in labial (A1) and lingual (A2) views. B. SNM Z 27444, bed 13, lower tooth in labial (B1) and lingual (B2) views. C. SNM Z 27465a, bed 20–21, lower posterior tooth in labial (C1) and lingual (C2) views. D. SNM Z 27465b, bed 5,?male lower tooth in labial view. E. SNM Z 27447, bed 5, lower symphyseal tooth in labial (E1) and lingual (E2) views. F. SNM Z 27448, bed 8–9, lower tooth in labial (F1) and lingual (F2) views. G. SNM Z 27449, bed 20–21, upper toot in labial (G1) and lingual (G2) views. H. SNM Z 27450, bed 20–21, upper tooth in labial (H1) and lingual (H2) views. I. SNM Z 27451, bed 20–21, upper tooth in labial (I1) and lingual (I2) views. J. SNM Z 27452, bed 17–18, upper tooth in labial view. K. SNM Z 27453, bed 8–9, upper tooth in labial (K1) and lingual (K2) views. L. SNM Z 27454, bed 21–22, upper posterior tooth in labial (L1) and lingual (L2) views.