Saurenchelys silex van Hinsbergh & Hoedemakers, 2022

Schwarzhans, Werner, 2023, Geology and stratigraphy of the Neogene section along the Oued Beth between Dar bel Hamri and El Kansera (Rharb Basin, northwestern Morocco) and its otolith-based fish fauna: a faunal inventory for the Early, Swiss Journal of Palaeontology (4) 142 (1), pp. 1-85 : 17

Saurenchelys silex van Hinsbergh & Hoedemakers, 2022

Figure 10f–h

2022 Saurenchelys silex —van Hinsbergh and Hoedemakers: pl. 1, Figs. 7 , 8 .

Material 2 specimens SMF PO 101.185 ( Fig. 10f ) and 2 juvenile specimens SMF PO 101.186 ( Fig. 10g –h ), Zanclean, Dar bel Hamri .

Description Small otoliths up to 3 mm in length are slen- der (OL:OH = 2.0–2.15), specimens from 4 to 6 mm in length are more compressed (OL:OH = 1.65–1.8); OH:OT = 2.1–2.2. Dorsal and ventral rims shallow, regular. Anterior tip slightly pointed; posterior tip blunt with rounded angles at junction with dorsal and ventral rims. All rims smooth.

Inner face flat with slightly inclined, centrally positioned, elongate oval and shallow sulcus filled with a single colliculum. OL:SuL = 2.5–2.6. Sulcus not extending anterior of colliculum. No dorsal depression and no ventral furrow. Outer face smooth, moderately convex, thickest behind the middle.

Discussion Nettastomatid otoliths show a low degree of morphological diversity, which renders identification difficult. Otoliths of representatives of all extant genera in the family are figured in Schwarzhans (2019b). Tose of Saurenchelys most closely resemble in otolith and sulcus shape. Saurenchelys cancrivora Peters 1864 is the only extant species in the genus occurring off West Africa (and in the Indo-West Pacific). Two extant otoliths figured ( Fig. 10i, j ) show a distinct variability in the shape of the postdorsal angle, which is pronounced in one specimen ( Fig. 10i ) and completely rounded in the other

( Fig. 10j ). Te index OL:OH ranges from 1.62 to 1.75. Saurenchelys silex described by van Hinsbergh & Hoedemakers, 2022, from the Piacenzian of Estepona near Málaga, Spain shows similar proportions in specimens of 4–5.5 mm in length, which is also matched with large specimens from Dar bel Hamri ( Fig. 10e ), but differs in the deepened ventral rim and the posterior thickening of the outer face. Two smaller specimens (3 mm in length) from Dar bel Hamri, however, are considerably more slender in shape and could potentially represent a second species. However, it is likely that this difference is due to allometric ontogenetic growth. Despite the lack of specimens of intermediate sizes the small specimens are, therefore, also placed in S. silex .

Figures

Fig. 10 Anguilliformes. a–d Panturichthys cf. fowleri (Ben-Tuvia, 1953), SMF PO 101.184 (a reversed), Dar bel Hamri. 10e, Echelus myrus (Linnaeus, 1758), SMF PO 101.216 (reversed), Dar bel Hamri. f–h, Saurenchelys silex van Hinsbergh & Hoedemakers, 2022, Dar bel Hamri, Zanclean, f SMF PO 101.186, g–h tentatively assigned specimens,SMF PO 101.815 (reversed). i–j, Saurenchelys cancrivora Peters, 1864, extant,West Pacific, i BSKU 69087, j BSKU 75296.k, Conger sp. juv., SMF PO 101.187 (reversed), Dar bel Hamri. l, Gnathophis mystax (Delaroche, 1809), SMF PO 101.188 (reversed),Dar bel Hamri. m, Japonoconger africanus (Poll, 1953), SMF PO 101.189 (reversed), Dar bel Hamri. n, Paraxenomystax cf. bidentatus Reid, 1940, SMF PO 101.273, Dar bel Hamri

Fig. 7 Photoplate of selected macrofossils from the Early Pliocene coquina of section 1, ca.1.5 km south of Dar bel Hamri. A rock sample is shown in n

Fig. 8 Conceptual structural cross-section through studied area based on Zizi (1996) and own field observations (scale 1:1). Subsurface thicknesses are extrapolated from sections of nearby wells published in Saadi et al. (1980) and Sani et al. (2006). Subsurface positions of not-exposed tectonic elements after Tilloy (1952), Zizi (1996), and Zouhri et al. (2002)