Misrichthys 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 : 11-12

Misrichthys sp.

Figure 4 H-K

2016 Misrichthys sp. ; Merzeraud et al., p. 14-15, tab. 1.

Material. The material consists only of three isolated teeth ( KEB 1-105 to 1-108; Figure 4 F-K), and numerous fragmentary crown, broken from KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia.

Description

Teeth are medium sized, reaching 14 mm height. The enameloid of crown is totally smooth both on lower and upper teeth. The upper teeth ( Figure 4 J-K) have a high triangular cusp, distally inclined in antero-lateral and posterior files. The mesial cutting edge is unserrated, convex, and not distinct from the mesial heel on our material. The distal cutting edge is also unserrated and concave but well separated from the short, rounded distal heel, sometimes angular, by a notch. Root is high with divergent lobes and a very large median groove in lingual view. The lower anterior tooth ( Figure 4H ) has a high and narrow cusp, the cutting edges are well marked but never reach the shortly and abrupt distal heel. The root is massive with a well-developed lingual protuberance bearing a very deep nutritive groove and two short lobes.

Remarks

Misrichthys was long considered as a Late Eocene monospecific genus having the ability to tolerate brackish to fresh waters (Murray et al., 2010) of Egypt, where it was often recorded (e.g., Case and Cappetta, 1990; Murray et al., 2010; Adnet et al., 2011; Underwood et al., 2011; Zalmout et al., 2012) until it was observed elsewhere (Adnet et al., 2010). This new report in Tunisia confirms that this genus was widely distributed along the Tethys seaway, and indicates that its occurrence is much older than the Late Eocene. Underwood et al. (2011) already reported rare specimens of a small and gracile species of Misrichthys (Underwood et al., 2011, figure 5Q) in MI (Late Lutetian – Early Bartonian), and suggested that an unnamed species of the genus was present in Wadi al Hitan before the Priabonian. Our report confirms the presence of a small species of Misrichthys since the Middle Bartonian, at least in Tunisia, but the scarcity of referred material and the tenuous distinction with the unique species M. stromeri (except a smaller size) are insufficient to describe a new species.

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.