Physogaleus secundus (Winkler, 1876)

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 : 20-21

Physogaleus secundus (Winkler, 1876)

Figure 9

1861 Galeocerdo minor Ag. ; Rogovich, p. 30, pl. IV, figs. 1-7.

1876 Trigonodus secundus n. sp.; Winkler,

p. 16-48, pl. 2, figs. A-F.

1905 Physodon secundus (Winkler) ; Leriche,

p. 189, pl. 8, figs. 6, 17, 18.

1912 Galeocerdo minor Ag. ; Savtchenko,

p. 170–171, pl. XIII, figs. 13-15.

1980 Physogaleus secundus (Winkler, 1876) ; Cappetta, p. 37, pl. 5.

1985 Striatolamia macrota (Agassiz, 1843) ; Bor, p. 95, pl. 3, figs. 3-8.

2002 Physogaleus secundus (Winkler, 1874) ; Dutheil et al., p. 758, fig. 4F, G.

2006 Physogaleus secundus (Winkler) ; Malyshkina, pl. 7, figs. 7-8.

2012 Physogaleus secundus (Winkler, 1876) ; Cappetta, p. 313-315, fig. 297.

2014 Physogaleus cf. secundus Winkler, 1876 ; Carlsen and Cuny, p. 61-62, fig. 14.

2019 Physogaleus secundus (Winkler, 1876) ; Ebersole et al., p. 95-98, fig. 34.

2019 Physogaleus secundus Winkler, 1876 ; Trif et al., p. 7-8, fig. 4.5-4.11.

Material. Three upper lateral teeth NMNHU-G 391/ 24/2-4, one lower anterolateral tooth NMNHU-G 391/24/1, one lower lateral tooth, NMNHU-G 391/ 24/5, Vyshhorod.

Description. The anterolateral tooth ( Figure 9B ) is quite large measuring 9.4 mm mesiodistally, 9.0 mm apicobasally, and 4.1 mm labiolingually. It has a slender and sigmoidal main cusp. The lingual face of the crown is convex, and the labial face is almost flat. The mesial cutting edge is long and faintly serrated near the base, whereas the distal edge is shorter and bears two rounded cusplets. The root has a lingual protuberance and deep central furrow.

The lateral teeth ( Figure 9A, C ) range in size from 7.8 to 9.9 mm mesiodistally (mean 8.6 mm), from 5.2 to 5.9 mm apicobasally (mean 5.6 mm), and from 2.2 to 2.5 mm labiolingually (mean 2.3 mm). The lower lateral tooth ( Figure 9C ) is slightly larger than the upper lateral ones. The sigmoidal crowns are angled distally. The mesial and distal edges of the main cusp are smooth. The base of the mesial cutting edge is slightly serrated, and there are four coarse triangular cusplets at the base of the distal cutting edge. The lingual and labial tooth surfaces are convex and the labial one overhangs the root. The root has a large lingual protuberance with a deep nutritive groove. The rectilinear basal root surface is nearly flat or slightly concave.

Remarks. The teeth are identical in morphology and size to those of Physogaleus secundus . The latter differs from other species of the genus in tooth size, cusp width, development of cusplets, and morphology of the cutting edge (Carlsen and Cuny, 2014; Ebersole et al., 2019; Trif et al., 2019). In particular, the teeth of P. secundus can be differentiated from those in the coeval species Physogaleus alabamensis (Leriche, 1942) by the number and strength of the mesial and distal denticles (Ebersole et al., 2019). The remains of P. secundus are known from the Eocene of Europe (Leriche, 1905; Bor, 1985; Dutheil et al., 2002; Cappetta, 2012; Carlsen and Cuny, 2014; Trif et al., 2019), Asia (Malyshkina, 2006), and North America (Maisch et al., 2015; Ebersole et al., 2019). It should be emphasised that Rogovich (1861) described a series of carcharinid teeth from Vyshhorod that he identified as Galeocerdo minor . This taxon originally was erected and figured by Agassiz (1835; Agassiz, 1833–1843, vol. 3, p. 232, pl. 26a, figs. 64-66, pl. 26, figs. 15-21) under the name Galeus minor . Woodward (1889) considered Galeocerdo minor to be valid but questioned its generic attribution. Although the locality and age of the original sample were unknown, Agassiz (1843) assumed that it probably came from Tertiary deposits of the Swiss Molasse Basin. Galeocerdo minor was reported from the Eocene of Belgium, England, the USA, and from the Miocene of France (Woodward, 1889). In addition, Savtchenko (1912) documented the remains of this taxon in the Eocene of Mangyshlak ( Kazakhstan). It is noteworthy that the latter was the last published reference to Galeocerdo minor in the literature. It is figured in the database compiled by Pollerspöck and Straube (2022) as Physogaleus minor (Agassiz, 1835) . We cautiously assume that P. minor and P. secundus could be conspecific, although such a revision is beyond the scope of our present study.

Figures

FIGURE 9. Teeth of Physogaleus secundus (Winkler, 1876) from the middle Eocene deposits of Vyshhorod: A – upper lateral tooth NMNHU-G 391/24/2; B – lower anterolateral tooth NMNHU-G 391/24/1; C – lower lateral tooth NMNHU-G 391/24/5, all in lingual view.