DASYATIDAE Jordan and Gilbert, 1879

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 : 32-33

Family DASYATIDAE Jordan and Gilbert, 1879

The recent revision of Last et al. (2016) about dasyatids has profoundly shaken our understanding of the systematics of fossil teeth with modern dasyatid design that have long been attributed to Dasyatis alone, or more recently to Himantura . To date, no available study of tooth morphologies within and between the most diversified subfamilies ( Dasyatinae , Neotrygoninae , and Urogymininae) is available due to incompleteness of tooth figuration (Guinot et al., 2018). Only Hypolophinae (gathering all the species of Pastinachus ) have a tooth morphology that is atypical enough to be clearly identified among fossil and living dasyatids (see also Adnet et al., 2019). However, and despite a very partial knowledge of the morphological diversity within each of the rare figured genera (e.g., Herman et al. 1998, 1999, Hovestadt and Hovesdtat-Euler, 2010; Cappetta, 2012; Marrama et al., 2018), it seems that most of the subfamily dasyatins sensu Last et al. [2016; e.g., Dasyatis pastinaca (Linnaeus, 1758) , D. sabina (Lesueur, 1824) , Bathytoshia centroura (Mitchill, 1815) , Pteroplatytrygon violacea (Bonaparte, 1832) ] and neotrygonins sensu Last et al. [2016; e.g., Neotrygon kuhlii (Müller and Henle, 1841) , Taeniura lymma (Forsskal, 1775) ] have jaws presenting a marked sexual heterodonty with male (and sometimes female) teeth displaying a long, tapered cusp in all or some tooth files.

Conversely, urogynminins sensu Last et al. (2016) have numerous species with a tooth morphology without well-detached cusp [e.g., Fontitrygon margarita (Günther, 1870) , Fontitrygon margaritella Compagno and Roberts, 1984 , Himantura uarnak (Gmelin, 1789) , Urogymnus asperrimus (Bloch and Schneider, 1801) , Fluvitrygon signifier (Compagno and Roberts, 1982) ]. Only a complete revision of the dental morphology of living taxa reviewed in this recent phylogenetic framework could allow a better and more accurate fossil identification of dasyatid genera. However, the presence of a cusp in the fossil dasyatid tooth sample can tentatively help for identification at the subfamily rank despite the knowledge of periodic shifts in male dentition from a female-like molariform to a recurved cuspidate form only during the reproductive season (Kajiura and Tricas, 1996).

Sub family NEOTRYGONINAE Last et al., 2016

Genus MECOTRYGON nov. gen.

zoobank.org/ F3C2C37C-A6C7-4225-BC7E-85D3F56AD72C

Type species. Mecotrygon asperodentulus nov. sp.

Etymology. From the acronym “MECO” (Middle Eocene Climatic Optimum) and Latin “trygon” that means stingray from the MECO event.

Temporal range. Uppermost Lutetian – lowermost Bartonian ( Egypt) to middle Bartonian ( Tunisia).

Diagnosis. Genus only known by isolated teeth with typical dasyatid design. Characterized by the presence of rugose crown marked by a sinuous transversal keel and secondary crests that tend to form an inner basin on the labial face. Cuspidate teeth have a small and thick cusp with a flat top extremity. The root could be high in anterior teeth with reduced rounded root lobes in lingual view.