Isurolamna gracilis ( Le Hon, 1871 )

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 : 47

Isurolamna gracilis ( Le Hon, 1871)

(Figs 37–44)

1871 Oxyrhina gracilis n. sp. – LE HON, p. 11, text-fig. 2.

1933 Lamna rupeliensis Le Hon – WEILER, p. 24, text-fig. 12.

1993 Lamna rupeliensis ( Le Hon, 1871) – BAUT, p. 4, figs 8–9.

2001 Isurolamna gracilis ( Le Hon, 1871) – REINECKE et al., pp. 21–23, pls 31, 32 (with fig. b), 33, 34. 2005 Isurolamna gracilis ( Le Hon, 1871) – REINECKE et al., p. 30, pl. 20, figs 4–6.

2012 Isurolamna gracilis ( Le Hon, 1871) – CAPPETTA, p. 217, fig. 202.

Referred material:5teeth(VER2016.3416., VER2016.3427.,VER2016.3436., VER 2016.3437., VER 2016.3438.).

Remarks: The crown is pointed and triangular, slender and narrow on lower files (Figs 37–39), while labiolingually and mesiodistally wide at the base on uppers. Both faces are smooth, the cutting edges are smooth all along, in continuing in the edges of the flattened lateral cusplets both mesially and distally. The lateral cusplets are low, typically rounded, or triangular, and pointed. On the lingual side the root bears a wide, convex crest, runs mesiodistally between the lateral cusplets, under the root-crown boundary. The root has two large, flattened lobes, with a visual nutritive groove in the middle. The lobes are angled on their mesial and distal edges. The anterior teeth are typically straight (or nearly straight), while the laterals and distals have distally directed main crown (Figs 40–44). Teeth of upper and lower jaw are easily distinguishable due to the dignathic heterodonty.

We assign a possible relation to I. gracilis , since the presence of lateral cusplets is not typical for Isurus oxyrinchus (reported from the Chattian of Germany; REINECKE et al. 2005, 2014). Hopefully later on more better preserved Kiscell Clay specimens of this species are going to be re-discovered in museum collections.

WEILER (1933, p. 24, text-fig. 12) reported and figured I. gracilis as Lamna rupeliensis from the Kiscellian of Budapest, but his figured specimen seems to be lost. However, other specimens have been found in the HNHM collection, labelled as Lamna rupeliensis , but these remains are fragmentary, and do not give any additional information to our description.

During the Rupelian Isurolamna gracilis was the predominant lamnid shark ( REINECKE et al. 2014).