Alopias cf. exigua ( Probst, 1879 )

Szabó, Márton & Kocsis, László, 2016, A preliminary report on the Early Oligocene (Rupelian, Kiscellian) selachians from the Kiscell Formation (Buda Mts, Hungary), with the re-discovery of Wilhelm Weiler’s shark teeth, Fragmenta Palaeontologica Hungarica 33, pp. 31-64 : 51-52

Alopias cf. exigua ( Probst, 1879)

( Figs 51–60 )

1879 Oxyrhina exigua n. sp. – PROBST, p. 135, pl. 2, figs 20–25.

1938 Isurus leptodon Ag. (= Isurus gracilis Le Hon. ) – WEILER, pp. 7–8, pl. 1, fig. 17.

1999 Alopias exigua ( Probst, 1879) – BAUT & GÉNAULT, p. 27, pl. 7, figs 8–10.

2001 Alopias exigua ( Probst, 1879) – REINECKE et al., pp. 23–24, pl. 35.

2007 Alopias exigua ( Probst, 1879) – KOCSIS, pp. 34–35, figs 5.13–5.14.

2013 Alopias exigua ( Probst, 1879) – SCHULTZ, p. 38, pl. 4, figs 15a, b.

2014 Alopias aff. exigua ( Probst, 1879) – REINECKE et al., pp. 23–27, pls 23, 24, pl. 25, figs 1–6.

Referred material: 4 teeth (V.61.840., V.61.853., VER 2016.3410., VER 2016.3451.).

Remarks: The teeth have narrow crown with bifurcated root. The crown is weakly curved labiolingually, it is smooth, and bears no striations. The lingual face is strongly, while the labial is weakly convex. The cutting edges are smooth all along, they usually do not reach the root-crown boundary ( KOCSIS 2007). The enamel continues towards the root lobes in forming a well-developed enamel shoulder ( Figs 53, 57, 60 ). This shoulder is wide and it weakly overhangs the root on the labial side ( Figs 52, 56, 59 ). The two root lobes typically form a squared to C-like shape in labiolingual view. A well-developed nutritive groove can be seen on the lingual face of the root. No lateral cusplets are present. While the anteriors are typically straight, the laterals curve distally. The visual sinuouslike curvature of the mesial cutting edge of the distals (especially of the upper distals) is typical feature.

WEILER (1938, pl. 1, fig. 17; also Fig. 54 of this work) figured a tooth as Isurus leptodon . One Kiscell Clay shark tooth of the HNHM collection is labelled as Isurus lepdonon (VER 2016.3451., Figs 51–53 ; most probably misspelled while cataloguing), and three others (V.61.840., V.61.853., VER 2016.3410.) have been found with similar morphology. The visual enamel-shoulder, the overhanging crown-enamel on the lingual side, and the shape of the root are all can be seen on the specimens, therefore, they are identified as possible remains of Alopias exigua . Weiler’s illustration is not detailed enough and drawn in a strange angle ( Fig. 54 ), still it shows some resemblance to VER 2016.3451. Because this specimen was found among other Kiscell Clay specimens of Weiler, and also catalogued as I. leptodon (misspelled, as Isurus lepdonon ), therefore it might be the illustrated tooth of Weiler (see Figs 51–54 ).

The genus is known from the Eocene, the species itself has been reported from the Early Oligocene to the Middle Miocene ( CAPPETTA 1987). Nowadays, three nominal species of thresher sharks live, these are A. pelagicus , A. superciliosus , and A. vulpinus ( POLLERSPÖCK & STRAUBE 2016) . These sharks live in pelagic waters, and A. superciliosus prefers deep waters ( CAPPETTA 2012).

Figures

Figs 51–60. Alopias cf. exigua (Probst, 1879). – 51–53. Anterior tooth (VER 2016.3451.). – 51. Lingual view. – 52. Profile view. – 53. Labial view. – 54. Anterior tooth figured by WEILER (1938), which shows some similarities to the specimen of VER 2016.3451. – 55–57. Anterior tooth (V.61.840.). – 55. Lingual view. – 56. Profile view. – 57. Labial view. – 58–60. Anterior tooth (V.61.853.). – 58. Lingual view. – 59. Profile view. – 60. Labial view. Scale bars: 5 mm