Scoliodon cf. laticaudus Müller & Henle, 1838

Jirapatrasilp, Parin, Cuny, Gilles, Kocsis, László, Sutcharit, Chirasak, Ngamnisai, Nom, Charoentitirat, Thasinee, Kumpitak, Satapat & Suraprasit, Kantapon, 2024, Mid-Holocene marine faunas from the Bangkok Clay deposits in Nakhon Nayok, the Central Plain of Thailand, ZooKeys 1202, pp. 1-110 : 1-110

Scoliodon cf. laticaudus Müller & Henle, 1838

Fig. 29

cf. Carcharias (Scoliodon) laticaudus Müller & Henle, 1838: 28 – 29 , pl. 8. Type locality: India.

cf. Scoliodon laticaudus . Compagno 1984: 534 – 535, with in-text figs. Krajangdara et al. 2022: 62, with in-text figs.

Referred material.

CUF - NKNY - S 3 – S 5 (Fig. 29 A – O ) (3 teeth).

Description.

The specimen CUF - NKNY - S 3 is a small and elongated tooth with a low crown and a worn off root. The mesial cutting edge is concave and smooth and continues along the mesial heel. The distal edge of the crown is convex and separated by a notch from a distinct distal heel.

The specimen CUF - NKNY - S 4 is a well-preserved tooth, with a crown strongly curved distally. The mesial cutting edge is sinusoid, starting convex, then becoming concave towards the apex. The apex of the crown overhangs distally the basal part of the tooth. The distal cutting edge is also sinusoid, though less so than the mesial one, and it is separated by a distinct notch from a well-developed distal heel. The enameloid of the crown extends more basally on the labial side of the tooth. The root is thick and the lobes run rather horizontally. It bears a well-developed and deep nutritive groove in the centre.

The cusp of the specimen CUF - NKNY - S 5 is strongly sigmoid in labial and lingual view, and similar to that of CUF - NKNY - S 4, but its cusp is narrower and less wide at the base, with more apparent mesial heels. The cutting edge is smooth and does not reach the apex of the cusp on its mesial side. The heels of the crown display faint serrations. The root is asymmetric and projected lingually and distally. There is a well-defined groove distally on the lingual side of the basal face, forming a deep notch in apical view.

Habitat.

Tropical zones of continental and insular shelves close to inshore, frequently in rocky areas ( Compagno 1984).

Distribution.

Indian Ocean; Indo-West Pacific, from Japan to Indonesia ( Compagno 1984).

Record in Thailand.

Andaman Sea ( Krajangdara et al. 2022).

Taxonomic remarks and comparisons.

The three teeth best fit the dentition of the modern species S. laticaudus (spadenose shark). The specimen CUF - NKNY - S 5 has a slender sigmoidal cusp and its mesial cutting edge does not reach the apex. It displays an asymmetric root, corresponding perfectly to a parasymphyseal tooth of a male specimen ( Herman et al. 1991). The specimen CUF - NKNY - S 4 likely represents an upper anterior-anterolateral tooth, whereas the specimen CUF - NKNY - S 3 is probably a lower anterolateral tooth (see Springer 1964: fig. 3 a). White et al. (2010) recognised another species, S. macrorhynchos , in the Western Pacific, meanwhile a molecular study also indicates the possible third Scoliodon species from the region ( Lim et al. 2022), hence these fossil teeth are described in open nomenclature.

It may be mentioned that the specimen CUF - NKNY - S 3 also resembles that of the lower anterolateral teeth of other common sharks in Southeast Asia ( Krajangdara et al. 2022) such as Loxodon macrorhinus (sliteye shark) and two Rhizoprionodon species, R. acutus (milk shark) and R. oligolinx (grey sharpnose shark). For the teeth of Loxodon , the apex of the crown is higher and somewhat aligned in a more distal position than that of the specimen CUF - NKNY - S 3 ( Springer 1964: fig. 4; Bass et al. 1975: pl. 8). The teeth of R. oligolinx seem to have a less concave mesial cutting edge ( Springer 1964: fig. 13), whereas for R. acutus , the distal heel appears less elongated and vertically higher, but a clear distinction is difficult here ( Springer 1964: fig. 6; Bass et al. 1975: pl. 9).

Figures

Figure 29. Carcharhinid shark teeth - Scoliodon cf. laticaudus A – E specimen CUF - NKNY - S 3, lower anterolateral tooth in A lingual B labial C mesial D distal and E apical views F – J specimen CUF - NKNY - S 4, upper anterior-anterolateral tooth in F lingual G labial H mesial I distal and J apical views K – O specimen CUF - NKNY - S 5, parasymphyseal tooth in K lingual L labial M mesial N distal and O apical views.