Macrorhizodus cf. praecursor (Leriche, 1905)

Artüz, M. Levent & Sakinç, Mehmet, 2025, Description of a new species, Xiphodolamia maliki sp. nov. and the shark teeth of Middle Eocene (Lutetian) aged Soğucak Formation in Küçükçekmece, Istanbul, Turkey, Zootaxa 5646 (4), pp. 527-544 : 533-535

† Macrorhizodus cf. praecursor (Leriche, 1905)

Material: Thirty-one poorly preserved teeth in the Malik Sayar Collection. 10 anterior teeth, 3 intermediate teeth, 9 lateral teeth, and 9 symphysial teeth were bulk-stored with their original labels and re-QR coded under the number MS10-001.00 ( Fig. 3a ).

Locality: On the eastern shore of the Küçükçekmece Lagoon ( Fig. 4 ; 5 ) in the Lutetian-aged level, Soğucak Formation ( Fig. 6 ).

Description and remarks: The fossilised set of 30 teeth is attributed to Macrorhizodus spp. based on distinct morphological characteristics. Each tooth displays a slender, elongated crown with a smooth, non-serrated cutting edge, typical of this genus. The crowns are labio-lingually compressed, narrow, and triangular, with a hook-like, dagger-shaped form terminating in a sharp apex. The distal edge is slightly convex, while the mesial edge is straight or subtly concave. The crown is symmetrical and angled, with a convex labial face and a slightly concave lingual face, and an apron is present on the labial surface. The basal portions of the root are missing, hindering assessment of lateral cusplets. These features, including the smooth edges, symmetrical triangular shape, and lack of serrations or basal cusps, align with diagnostic characteristics of genus Macrorhizodus .

While poor preservation and absence of roots are observed, possibly due to fossilisation conditions or handling, the morphology of these specimens is consistent with Macrorhizodus cf. praecursor , a species noted for its broad distribution in the Tethys Ocean during the Middle Eocene to Early Oligocene ( Popov et al. 2024). Some studies restrict M. praecursor to the Lutetian stage (e.g., Trif et al. 2019; Asan et al. 2022), while others extend its range from the Eocene into the Oligocene (e.g., Cappetta, 1987; Otero et al. 2015). This species has been reported in various regions, including the lowermost Bartonian of Transylvanian Basin, Romania ( Trif, 2019), the Middle Eocene of Dnieper-Donets Basin, Ukraine ( Kovalchuk et al. 2023), and the Eocene Lutetian deposits of Virginia's Piney Point Formation ( Ward and Wiest, 1990).

These morphological traits and the characteristic shape, size, and stratigraphic positioning of the specimens support classification within genus Macrorhizodus , consistent with cf. praecursor (Leriche, 1905) as referenced by Ebersole et al. (2019) and Cappetta (2012). This represents the first documented occurrence of genus Macrorhizodus within the Middle Eocene (Lutetian) Soğucak Formation in Küçükçekmece, Istanbul, Turkey.

Autecology: During the Lutetian age, a presumed extinct ancestral taxon of I. oxyrinchus , Macrorhizodus praecursor , likely inhabited ancient oceans as a pelagic predator. This genus is known for its highly migratory behaviour, and its fossil form during the Lutetian age would likely have had a similar ecological niche as its extant counterparts. Based on findings from fossil specimens, it is suggested that the Macrorhizodus praecursor during the Lutetian age would have played a role in the marine ecosystem as an efficient and powerful apex predator, preying on a various smaller marine animals ( Uhen, 2007).

Figures

FIGURE 3. A) Teeth of Macrorhizodus cf. praecursor (a–c) selected palatoquadrate anterior tooth, a) labial view; b) distal view; c) lingual view. (d–e) selected maxillar lateral tooth, d) labial view; e) lingual view. (f–g) selected mandibular lateral tooth, f) labial view; g) lingual view. B) Teeth of Otodus sokolovi (a–b) BA09-001.00, a) labial view; b) lingual view. (c–d) BA09-001.01, c) labial view; d) lingual view. Found in Eocene deposits (Soğucak Formation) during the years 1954–1955, Küçükçekmece, Istanbul, Turkey (Scale bars 10 mm).

FIGURE 4. Locality map showing the point (marked with a black dot) where the shark tooth fossils were collected. The Küçükçekmece Basin is located southeast of Küçükçekmece Lake (Lagoon) and is one of the major Tertiary sedimentary basins in Thrace, Turkey.

FIGURE 5. Generalized geological map of the location where the teeth were found, adapted from Arıç (Sayar), (1955)

FIGURE 6. Generalized stratigraphic columnar section of the Küçükçekmece Basin (explained in text).