Rhizoprionodon sp.

Adnet, Sylvain, Marivaux, Laurent, Cappetta, Henri, Charruault, Anne-Lise, Essid, El Mabrouk, Jiquel, Suzanne, Ammar, Hayet Khayati, Marandat, Bernard, Marzougui, Wissem, Merzeraud, Gilles, Temani, Rim, Vianey-Liaud, Monique & Tabuce, Rodolphe, 2020, Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia, Palaeontologia Electronica (a 38) 23 (2), pp. 1-62 : 12

Rhizoprionodon sp.

Figure 4 L-R

2016 Rhizoprionodon sp. ; Merzeraud et al., p. 14-15,

tab. 1. Material. A hundred broken upper and lower teeth from the KEB-1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia (including those figured, KEB 1-126 to 1-132; Figure 4 L-R).

Description

Teeth are relatively small (5 mm in length), labial face of root is slighlty concave and the basal edge of root is well rounded, except near the nutritive notch. The main cusp is relatively high (especially in most anterior lower teeth; Figure 4O ) and without serration. Finely serrated, the distal heel of the crown is interrupted by a small notch in lateral teeth, sometimes marking a low cusplet ( Figure 4R ).

Remarks

First recorded in the Early Eocene of Morocco (Arambourg, 1952), Cenozoic evidence of the genus Rhizoprionodon is relatively common in tropical deposits of the Tethys seaway during the Late Eocene, from the Caribbean sea to the Jordanian coast (e.g., Case, 1981; Mustafa and Zalmout, 2002), leading some authors to propose that the current distribution of the seven recent species, today unknown in Mediterranean sea, is most likely a result of a former widespread distribution along Tethyan mangroves in the mid-Cenozoic, affected by successive vicariance events (Briggs, 1995; Musik et al., 2004; Gallo et al., 2010). It is noteworthy that certain extant species of Rhizoprionodon are possibly known since Late Eocene deposits but distinctive specific characters on teeth suffer from a conservative dental morphology among genera, as observable in the literature devoted to those taxa (Springer, 1964; Compagno, 1988; Herman et al., 1991). By combination of a pointed cusp out with the lack of serrated cutting edges, this unnamed fossil species seems quite different from several extant species, but resembles the Ypresian Rhizoprionodon gantourensis (Arambourg 1952) , the Neogene Rhizoprionodon fisheuri (Joleaud, 1912) , frequently recorded in Miocene deposits of Mediterranean or the extant Rhizoprionodon lalandii (appendix 2 Fig. D) and Rhizoprionodon acutus (appendix 2 Fig. C), recorded since the Zanclean deposits of south and north Mediterranean coasts (e.g., Cappetta and Cavallo, 2006; Pawellek et al., 2012). Besides the fact that tooth morphology of fossil Rhizoprionodon is quite conservative, dignatic and gynandric heterodonties are frequently observed in fresh jaws of Recent representatives. Its use in systematics appears highly uncertain.

Figures

FIGURE 4. A-B: Carcharhinus kasserinensis nov. sp., A. Antero-lateral upper tooth of young specimen KEB 1-098, A1. Lingual view, A2. Labial view; B. Antero-lateral upper tooth of young specimen KEB 1-099, labial view. C-G: Carcharhinus frequens. C. Lateral upper tooth KEB 1-100, C1. Labial view, C2. Lingual view; D. Lateral upper tooth KEB 1-101, D1. Labial view, D2. Lingual view; E. Anterior lower tooth KEB 1-102, E1. Labial view, E2. Lingual view; F. Lateral lower tooth KEB 1-103, F1. Labial view, F2. Lingual view; G. Posterior lower tooth KEB 1-104, lingual view; H- K: Misrichtys sp. H. Anterior lower tooth KEB 1-105, lingual view; I. Lateral upper tooth KEB 1-106, labial view; J. Posterior lower tooth KEB 1-107, j1. Labial view, J2. Lingual view; K. Lateral upper tooth KEB 1-108, labial view; L-R: Rhizoprionodon sp. L. Anterior upper tooth KEB 1-126, labial view; M. lateral upper tooth KEB 1-127, labial view; N. Lateral upper tooth KEB 1-128, labial view; O. Anterior lower tooth KEB 1-129, labial view; P. Lateral lower tooth KEB 1-130, P1. Labial view, P2. Lingual view; Q. Posterior lower tooth KEB 1-131, labial view; R. Antero-lateral lower tooth KEB 1-132, R1. Labial view, R2. Lingual view.