Otodus sokolovi (Jaeckel, 1895)

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 : 535-536

† Otodus sokolovi (Jaeckel, 1895)

Material: Two anterior teeth in the Malik Sayar Collection ( Fig. 3 B ). BA09-001.00; BA09-001.01.

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 two fossilised teeth exhibit characteristic features consistent with the genus Otodus . It has a large, robust crown with a triangular outline and finely serrated cutting edges along the entire length. The serrations are uniform, indicative of efficient shearing functions. The distal cutting edge is convex, while the mesial edge is predominantly straight with slight convexity in the upper third. Lateral cusps are not preserved, likely lost during fossilisation or post-mortem processes, but their positions are discernible, distinguishing it from some related species. The lingual side displays a well-developed neck, while the root is broad and thick, showing minor wear and chipping on the mesial side.

The specimens show two well-preserved Otodus sokolovi teeth with distinctive morphological features that aid in the identification of this species. Both teeth present the classic triangular shape with robust crowns and wide bases. The crowns are broad and triangular with relatively smooth surfaces. The enamel is well preserved, showcasing a clean, sharp edge along the lateral sides. The cutting edges are finely serrated, with serrations extending from the apex of the crown to the base. These serrations are regular and fine, consistent with typical O. sokolovi dental traits.

The larger tooth (BA09-001.00) measures approximately 51.7 mm in total and 32.5 mm in crown length, fitting well within the typical size range for O. sokolovi teeth ( Fig. 3 B a–b ). The smaller tooth (BA09-001.01) (46.6 mm in total, 31.4 mm crown length) is on the smaller end for O. sokolovi teeth but still within a typical range, retaining the triangular shape ( Fig. 3 B c–d ), though slightly more compact, likely representing a lateral tooth from a different position in the jaw. The smaller tooth likely belongs to a relatively young individual, as typical underdeveloped cusplet formation can be observed on the right side in the labial direction of the tooth ( Fig. 3 B ). The roots appear thick and robust, though somewhat eroded. The visible root structure in both teeth is characteristic of the genus, with a broad base supporting the crown. The bifurcation is not clearly visible due to wear and fossilisation, but its general thickness and curvature indicate a strong attachment point in life.

The serrations are sharp and closely spaced, which is typical of O. sokolovi teeth and essential for distinguishing them from related species. In the larger tooth, the serrations are particularly well preserved along the mesial and distal edges, tapering evenly toward the apex. The serrations in the smaller tooth show slight wear, though they remain identifiable and regular.

Despite their excellent preservation, the lateral cusplets are missing, likely due to fossilisation or post-mortem processes. However, aside from this, both teeth exhibit remarkable preservation, particularly with regard to the enamel and serration integrity. Both teeth show some wear at the root and slight discolouration from fossilisation and overall preservation of the teeth is good.

These teeth, collected by Malik Sayar from the Küçükçekmece stone quarries between 1954 and 1955, are the first record of Otodus sokolovi teeth from the Lutetian-aged level of the Soğucak Formation in Turkey.

Autecology: Otodus sokolovi was a dominant apex predator in marine ecosystems about 47.8– 41.3 m.y. ago (Lutetian, early Middle Eocene), as well as in the Tethys realm around the African-Eurasian shallow marine habitats ( Diedrich, 2013). As a highly specialised macropredator, it primarily inhabited warm coastal environments, though fossil evidence indicates its presence in a variety of marine habitats, ranging from shallow coastal waters to deeper offshore regions ( Popov et al. 2024).

Its size, estimated at over 5 meters in length ( Trif et al. 2016), allowed O. sokolovi to target large marine vertebrates, including cetaceans (whales, dolphins, and sirenians), pinnipeds (seals), and large fish ( Diedrich, 2013). Juveniles likely occupied more sheltered coastal nurseries, preying on smaller fish and marine mammals until they reached sizes that allowed them to transition to open-ocean environments.

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).