Hexanchus agassizi Cappetta, 1976

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 : 8

Hexanchus agassizi Cappetta, 1976

Figure 4A–C

1861 Notidanus microdon Ag. ; Rogovich, p. 29, pl. III, figs. 25, 26.

1886 Notidanus serratissimus Ag. ; Woodward, p. 216, pl. VI, figs. 24, 26.

1899 Notidanus serratissimus Ag. ; Woodward, p. 6, pl. I, fig. 7.

1928 Notidanus serratissimus Ag. ; Menner,

p. 294, pl. X, fig. 1.

1964 Notidanus serratissimus Ag. ; Glickman,

p. 157, pl. VI, fig. 5-5a; pl. XXVI, fig. 22.

1966 Notidanus serratissimus Ag. ; Casier, p. 44, pl. 1, figs. 10-12.

1967 “Nodidanus ” serratissimus Ag. ; Pledge,

p. 140, pl. 1, fig. 2.

1976 Hexanchus agassizi nov. sp.; Cappetta,

p. 553-554, pl. 1, figs. 5-8.

1979 Hexanchus agassizi Cappetta, 1976 ; Ward, p. 114-115, pl. 2, figs. 1, 2.

2005 Hexanchus agassizi Cappetta, 1976 ; Mustafa et al., p. 405-406, figs. 3-5.

2006 Hexanchus agassizi Cappetta ; Malyshkina, pl. 12, fig. 4.

2006 Hexanchus cf. agassizi Cappetta, 1976 ; Udovichenko, p. 203, pl. I, fig. 1.

2012 Hexanchus agassizi Cappetta, 1976 ; Cappetta, p. 92-93, fig. 82.

2012 Hexanchus agassizi Cappetta, 1976 ; Zalmout et al., p. 74, fig. 3A.

2013 Hexanchus agassizi Cappetta, 1976 ; Otero et al., fig. 5.1-6.

2013 Hexanchus agassizi Cappetta, 1976 ; Schultz, p. 23-24, pl. 4, figs. 4a, b, 5.

2016 Hexanchus agassizi Cappetta, 1976 ; Szabó and Kocsis, p. 38-40, figs. 14-17.

2017 Hexanchus agassizi Cappetta, 1976 ; Zalat et al., p. 204, pl. 1, fig. 15.

2021 Hexanchus agassizi Cappetta, 1976 ; Adnet et al., p. 44, fig. 12.1-12.2.

Material. One upper left anterolateral tooth,

NMNHU-G 391/21/2; two lower (left and right) lateral teeth, NMNHU-G 391/21/3, 391/21/4, Vyshhorod.

Description. The upper anterolateral tooth (Figure

4A) is 8.7 mm long mesiodistally and 8.3 mm high.

The root is robust and wide, it has a striated ornamentation on its lingual face, and a shallow longitudinal groove on the smooth labial face. There is a long and sharp central cusp oriented posteriorly to the tooth base. A small lateral cusplet is separated from the central cusp with a deep arcuate notch. Edges of the central cusp and the cusplet are laterally compressed.

The lower lateral teeth ( Figure 4B–C ) are also small (11.9 and 11.3 mm wide), about two times wider than high. The root is compressed labiolingually with a concave mesial edge and bears numerous small foramina on both the labial and lingual faces. There are eight to nine cones (including the acrocone) decreasing in height distally. The acrocone is slightly more developed than the first accessory cone; its mesial edge is serrated near the base in one of the specimens, whereas it is smooth in the second tooth. The L2/L3 ratio (see Adnet, 2006a for details) is 0.8 and 0.9, that is, L2<L 3 in both cases. The number of cusps per tooth width equals 7.3 and 7.5.

Remarks. The teeth are morphologically identical to and metrically close to those in Hexanchus agassizi Cappetta, 1976 . The specimens described are somewhat similar to those in Notorynchus primigenius (Agassiz, 1843) but differ by their smaller size and having more numerous accessory cones. The estimated length of the body (based on lower lateral teeth), following the equations in Compagno (1984) and Adnet (2006a), could have reached 129 and 136 cm. Hexanchus agassizi had a worldwide distribution during the Eocene (Cappetta, 2012). The presence of this species (also under the name Notidanus serratissimus Agassiz, 1843 ) is documented in the Eocene fossil record of Europe (Woodward, 1886, 1899; Casier, 1966; Cappetta, 1976; Ward, 1979; Dutheil, 1991; Adnet, 2006a; Adnet et al., 2008), Asia (Menner, 1928; Glickman, 1964; Case et al., 1996; Zhelezko and Kozlov, 1999; Mustafa et al., 2005; Malyshkina, 2006), Africa (Dartevelle and Casier, 1943; Zalmout et al., 2012; Zalat et al., 2017), South and North America (Case, 1981; Otero et al., 2013), and Australia (Pledge, 1967; Kemp, 1978). Adnet (2006a) considered H. agassizi to be the only lower–middle Eocene species of Hexanchus , whereas other taxa described from coeval deposits ( Hexanchus collinsonae Ward, 1979 and Hexanchus hookeri Ward, 1979 ) may represent different ontogenetic stages of this species.

Figures

FIGURE 4. Hexanchiform, heterodontiform and lamniform shark teeth from the middle Eocene deposits of Vyshhorod: A-C – Hexanchus agassizi Cappetta, 1976, upper anterolateral tooth NMNHU-G 391/21/2 (A), lower lateral teeth NMNHU-G 391/21/3 (B) and NMNHU-G 391/21/4 (C); D-E – Notorynchus kempi Ward, 1979, upper anterolateral tooth NMNHU-G 391/20 (D), lower lateral tooth NMNHU-G 391/21/1 (E); F – Heterodontus sp., lateral tooth NMNHU- G 391/6; G-M – Striatolamia macrota (Agassiz, 1843), upper lateral teeth NMNHU-G 391/105 (G-H), NMNHU-G 391/ 54 (I-J), NMNHU-G 391/55 (K-L), upper posterior tooth NMNHU-G 391/92 (M); N-O – Brachycarcharias lerichei (Casier, 1946), lower lateral tooth NMNHU-G 391/52. Lingual view in A, H, J-K, M, and O, labial view in B-G, I, L, and N.