Arechia 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 : 37-38

Arechia sp.

Figure 12 P-Q

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

Material. Sixty teeth, including those figured KEB 1-203, 1-204 ( Figure 12 P-Q) from the KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia.

Description

Teeth are relatively large, reaching 3 mm long for the largest one. The dentition is characterized by a moderate gradient of monognathic heterodonty, with high-crowned teeth, which decrease in size toward the commissure. The enameloid of crown is entirely smooth, except the presence of soft wrinkles along the labial margin of the transversal keel in some teeth ( Figure 12Q 1 ). There is no detached cusp but the transversal keel can be substantially high, lingually oriented to vertically erected (e.g., Figure 12Q 2 ), with rarely a minute cusp medially centred. The transversal keel, fine and cutting, never reaches the lateral angles of crown, the labial and lingual faces being fused laterally. On many teeth, the cutting transversal keel appears isolated from the rest of the crown in occlusal view. As a result, the lateral angles are well delimited from the transversal keel by angular notches in labial or lingual views ( Figure 12Q 2 ). The lingual face shows a triangular shape and is concave except near the median, vertical keel. The labial face is regularly concave or flat, depending on the file position of teeth. The lingual visor is medially sinuous in lingual view ( Figure 12Q 2 ). The root is poorly developed, lingually oriented with two short lobes separated by a shallow groove where a large principal foramen opens medially. A secondary foramen always opens labially near the crown/ root boundary.

Remarks

Only one species of Arechia is known to date: A. arambourgi Cappetta, 1983 from the Late Ypresian of Morocco. However, several reports of the genus indicate a more widespread geographical and stratigraphical ranges (e.g., Cappetta and Traverse, 1988; Tabuce et al., 2005; Cappetta, 2012; Sambou et al., 2017). The KEB-1 dental material is comparable to that figured by Cappetta (1983 pl. 2), but it seems somewhat different from Arechia arambourgi in having a higher cutting transversal keel with a slight ornamentation on its inner border, prefiguring the appearance of a real large cusp. However, these differences are tenuous, and this material is left in open nomenclature.

Murray et al. (2014, figure 4K-?M) figured several teeth of Dasyatis sp. from the Rupelian JQ, Fayum, the morphology of which is strongly reminiscent of that of Arechia , having non-continuous transversal keel from one lateral angle to the other. Some of them (Murray et al., 2014, figure 4M) possess a relatively long detached “cusp” that seemly derives from a high cutting transversal keel. Whatever the validity of the latter attribution, we provisionally attribute the genus Arechia to Urotrygonidae incertae sedis, rather than to Dasyatidae incertae sedis because the living representatives Urobatis jamaicensis (Herman et al., 2000; Hovestadt and Hovestadt-Euler 2010) seems to be the unique figured taxa with dasyatoid tooth design with teeth having a non-continuous transversal keel from both lateral angles of the crown. Arechia clearly differs from representatives of living or fossil Urobatis (Hoverstadt and Hovestadt-Euler 2010, Pimiento et al., 2013) in having no secondary crest on the labial face of the crown nor so developed cusp. The occurrences of Arechia in the middle Bartonian of Tunisia (Djebel el Kébar) and possibly until the Rupelian of Egypt (Murray et al., 2014) increase significantly the stratigraphical range of this possible urotrygonid, a family distributed today throughout the tropical Pacific and Western Atlantic realms.

Figures

FIGURE 1. Paleotemperatures (ice-free deep-ocean T°/ tropical sea surface T°) and Thermic events during the “doubthouse” conditions of Eocene period (from Cramwinckel et al., 2018 modified with events dating from Hollis et al., 2019). Stratigraphically and geographical locations of the main deposits with Elasmobranch associations along the southwestern Tethys. Abbreviations: DAK: Dakhla (Adnet et al., 2010), GEN: Genam (Zouhri et al., 2017, in press); AZ: Aznag (Tabuce et al., 2005) PM: Phosphate ores (see Noubhani and Cappetta, 1997), Morocco; GAF: Gafsa basin (see Arambourg, 1952); KEBAR: Kébar (this work and Adnet et al., 2019); MBK: Mabrouk (see Sweydan et al., 2019), Tunisia; EG: ElGedida (see Strougo et al., 2007); KM: KM11 (see Adnet et al., 2011) MT: Minqar Tabaghbagh (see Zalmout et al., 2012); BQ: Birquet Qarun QS: Quar et Sa; GE: Genahamm Fm.; MI: Midawara FM. from Wadi al Hitan, see Underwood et al., 2011), Egypt; QD: Qa Faydat al Dahikya, Jordania, see Mustafat and Zalmout, 2002).

FIGURE 2. Locality of KEB-1, Djebel el Kébar, Kasserine region, Tunisia. A, Simplified topographic map of Tunisia locating the Djebel el Kébar in central Tunisia; B, simplified stratigraphical position of fossiliferous level having yielded the fossil-bearing KEB-1 locality; C, photograph showing the typical badlands of variegated clays from the early Tertiary sequence of Djebel el Kébar. See Merzeraud et al. (2016) for precise details about geological settings.

FIGURE 12. A-C. Mecotrygon asperodentulus nov. gen nov. sp. A. anterior tooth KEB 1-188, A1. occlusal view, A2. Profile, A3. Basal view; B. lateral tooth KEB 1-189, B1. occlusal view, B2. labial view, B3. Profile; C. lateral tooth KEB 1-190, HOLOTYPE, C1. Occlusal view, C2. Lingual view, C3. Basal view, C4. Profile; D-M. Himantura souarfortuna nov. sp. D.?posterior tooth KEB 1-191, D1. Occlusal view, D2. Profile, D3. Basal view; E. antero-lateral tooth KEB 1- 192, occlusal view; F. anterior tooth KEB 1-193, F1. Occlusal view, F2. Labial view; G. antero-lateral tooth KEB 1-194, G1. Occlusal view, G2. Profile; H. anterior tooth KEB 1-195, occlusal view; I. lateral tooth KEB 1-196, occlusal view; J. A. anterior tooth KEB 1-197, occlusal view; K. lateral tooth KEB 1-198, K1. Occlusal view, K2. Basal view; L. A. anterior tooth KEB 1-199, occlusal view; M. lateral tooth KEB 1-200, occlusal view. N-O. Dasyatoid indet. N. antero-lateral tooth KEB 1-201, N1. Occlusal view, N2. Basal view; O. A. antero-lateral tooth KEB 1-202, occlusal view; P-Q. Arechia sp. P. lateral tooth KEB 1-203, occlusal view; Q. A. anterior tooth KEB 1-204, Q1. Occlusal view, Q2. Lingual view.