Otodus (Carcharocles)

Kovalchuk, Oleksandr, Kriwet, Jürgen, Shimada, Kenshu, Ryabokon, Tamara, Barkaszi, Zoltán, Dubikovska, Anastasiia, Anfimova, Galina & Davydenko, Svitozar, 2023, Middle Eocene cartilaginous fishes (Vertebrata: Chondrichthyes) of the Dnieper-Donets Basin, northern Ukraine, Palaeontologia Electronica (a 32) 26 (2), pp. 1-37 : 16-18

Otodus (Carcharocles) sp.

Figures 6 I-P, 7A-M

1861 Carcharodon megalotis Ag. ; Rogovich, p. 36, pl. IV, figs. 14-16b.

1861 Carcharodon lanceolatus Ag. ; Rogovich,

p. 37, pl. IV, fig. 17; pl. 9, figs. 58, 58a.

1861 Carcharodon productus Ag. ?; Rogovich,

p. 37, pl. IV, figs. 18, 19.

Material. One upper lateral tooth, NMNHU-G 391/ 32; three lower anterolateral teeth, NMNHU-G 391/ 26, 391/29, 391/35, Vyshhorod; five isolated vertebrae, NMNHU-P PI 553, PI 554, PI 2314, PI 2315, PI 2316, Zoloti Vorota.

Description. The anterolateral and lateral teeth ( Figure 6I–P ) are large and wide, triangular or lanceolate in shape; all the specimens are broken near the crown-root junction. The total height of the crown is in the range of 39.1–46.8 mm with the maximum width of about 30 mm. Both crown faces are smooth; the lingual face is convex and the labial one is flat. The cutting edges are irregularly serrated with saw-like serrations from the rounded crown apex to the base.

The vertebrae specimens ( Figure 7A–M ) are represented by robust, well-calcified, disk-shaped centra, where the smallest one (NMNHU-P PI 554) measures 64 mm in diameter and 29 mm in anteroposterior length; the largest one (NMNHU-P PI 2314) measures 88 mm in diameter and 32 mm in anteroposterior length. They are characterised as ‘lamnoid vertebrae’ (Applegate, 1967) by exhibiting many radiating calcified lamellae (asterospondylic) connecting the two primary cones of unperforated amphicoelous calcification (corpora calcarea) (for terminology, see Ridewood, 1921; Newbrey et al., 2015). The walls of the pairs of circular to oval foramina for the basidorsal and basiventral cartilages (Welton and Farish, 1993) make direct contact with the corpora calcarea. Both articular surfaces exhibit many concentric growth bands.

Remarks. The tooth specimens from Vyshhorod are identical in morphology and size to those of Otodus (Carcharocles) auriculatus from the Eocene of Europe, Asia, and North America (e.g., Savtchenko, 1912; Glickman, 1964; Nolf, 1988; Zhelezko and Kozlov, 1999; Cappetta, 2012; Carlsen and Cuny, 2014; Maisch et al., 2015; Adnet et al., 2021). Zhelezko and Kozlov (1999) reported on the presence of a specific subspecies— Otodus auriculatus auriculatus (Blainville, 1818) —occurring in the Lutetian of Ukraine, Kazakhstan, and Central Asia. It differs from Otodus auriculatus disauris (Agassiz, 1843) in the presence of regular serrations on the cutting edges. While the state of preservation of the material described in this study is insufficient for identifying it closer than to genus level, the merit of such subspecies concept for the genus Otodus is uncertain. The specimens considered are represented by broken crowns only, therefore we do not speciate them. The five isolated vertebrae likely represent the same taxon due to their similar morphology and belong to a lamniform based on their ‘lamnoid’ type (see above). The tentative identification is based on their large vertebral sizes that precludes to be any other known lamniform taxa from the Eocene, and the fact that their morphology does not contradict with that of previously described vertebrae of O. auriculatus (Ehret and Ebersole, 2014) .

Lamniformes indet.

Figure 8 A-M

1861 Shark vertebrae; Rogovich, p. 63, pl. IX, figs. 6-6b, 11-16.

Material. Seven vertebrae, NMNHU-G 391/118, 391/119, 391/120, 391/121, 391/122, 391/136, 391/137, Vyshhorod.

Description. NMNHU-G 391/118, 391/119, 391/ 120, 391/121, and 391/122 represent five of the six vertebral centra that are considered to have come from a single vertebral column, which were found near Vyshhorod (Rogovich, 1861), whereas NMNHU-G 391/136 and 391/137 represent isolated vertebrae. All the vertebrae are represented by gracile but well-calcified, unperforated, amphicoelous centra with several thin radiating calcified lamellae. Their articular surfaces are circular ranging up to 44.1 mm in diameter and 19.4 mm in anteroposterior length (based on NMNHU-G 391/ 136). The walls of the pairs of robust circular to oval foramina for the basidorsal and basiventral cartilages make direct contact with the corpora calcarea. Many faint concentric growth bands are present on both articular surfaces of the vertebrae considered.

Remarks. The seven vertebrae described here exhibit a generally similar morphology, but whether all of them are conspecific cannot be ascertained. Similarly to the vertebrae of Otodus (Carcharocles) sp. (see above), the entire surface of the intermedialia (i.e., the body of each centrum between both sides of corpora calcarea) is rough because of the terminal edges of the radiating calcified lamellae, indicating that they are of ‘lamnoid type’ (see above). They differ from all other elasmobranch vertebrae described below by the surface of the intermedialia being either largely smooth or massive in appearance (except for the oval foramina for the basidorsal and basiventral cartilages) or having laterally oblong (non-circular) articular surfaces. However, because they are isolated finds with no associated teeth, their exact taxonomic identity beyond ‘ Lamniformes indet.’ is uncertain.

Figures

FIGURE 6. Lamniform shark teeth from the middle Eocene deposits of Vyshhorod: A-H – Macrorhizodus praecursor (Leriche, 1905), anterior teeth NMNHU-G 391/101 (A-B), anterolateral teeth NMNHU-G 391/103 (C-D), 391/69 (E-F), anterior tooth NMNHU-G 391/68 (G-H); I-P – Otodus (Carcharocles) sp., upper lateral tooth NMNHU-G 391/32 (I-J), lower anterolateral teeth, NMNHU-G 391/35 (K-M), lower anterolateral tooth NMNHU-G 391/26 (N-P). Labial view in A, C, E, G, I, K, and N, lingual view in B, D, F, H, J, M, and O, mesial view in L and P.

FIGURE 7. Vertebrae of Otodus (Carcharocles) sp. from the middle Eocene deposits of Zoloti Vorota (Kyiv): A-B – NMNHU-P PI 553; C-D, K – NMNHU-P PI 554; E-F – NMNHU-P PI 2314; G-H, M – NMNHU-P PI 2315; I-J, L – NMNHU-P PI 2316. Anterior view in A, C, E, G, and I, lateral view in B, D, F, H, and J. X-ray images are those in K-M (not to scale).

FIGURE 8. Lamniform vertebrae (Lamniformes indet.) from the middle Eocene deposits of Vyshhorod: A, F – NMNHU- G 391/118; B, G – NMNHU-G 391/119; C, H – NMNHU-G 391/120; D, I – NMNHU-G 391/121; E, J – NMNHU-G 391/ 122; K – NMNHU-G 391/136; L-N – NMNHU-G 391/137. Anterior view in A-E and K-L, posterior view in M, lateral view in F-J and N.