Mecotrygon asperodentulus, Adnet & Marivaux & Cappetta & Charruault & Essid & Jiquel & Ammar & Marandat & Marzougui & Merzeraud & Temani & Vianey-Liaud & Tabuce, 2020
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publication ID |
https://doi.org/ 10.26879/1085 |
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publication LSID |
lsid:zoobank.org:pub:B6B8E985-F1CF-4C10-BB00-602E5BF36C1C |
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persistent identifier |
https://treatment.plazi.org/id/03BA87C1-FFEC-FFF9-C030-E7C4CED2B62F |
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treatment provided by |
Felipe |
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scientific name |
Mecotrygon asperodentulus |
| status |
sp. nov. |
Mecotrygon asperodentulus nov. sp.
Figure 12 View FIGURE 12 A-C zoobank.org/ E23FAB91-7091-45F7-9A3A-6E878BCC583E
2007 Dasyatis sp. 1 ; Strougo et al., p. 88-94.
2016 Dasyatis sp. 1 ; Merzeraud et al., p. 14-15, tab.
1.
Etymology. Derived from the Latin “aspero” and “dentulus”, meaning rugose small teeth.
Type locality and stratum. KEB 1-190 ( Figure 12C View FIGURE 12 ) from the KEB-1 locality, Souar-Fortuna formations in Djebel el Kébar, Tunisia .
Other material. Additional material, including figured KEB 1-188 and 1-189 ( Figure 12A, B View FIGURE 12 ), consists of several hundred oral teeth from the KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia.
Diagnosis. As that of the monotypic genus.
Description
The dentition shows a gradual monognathic heterodonty with high-crowned teeth, which decrease in size toward the commissure. The majority of available teeth have a small, thick cusp on the crown, holotype included ( Figure 12C View FIGURE 12 ). This cusp is mainly medio-lingually oriented ( Figure 12A View FIGURE 12 2 View FIGURE 2 , B 3 View FIGURE 3 , C 4 View FIGURE 4 ), its top is peculiarly flat, parallel to the crown base and connected to the transversal keel separating the smooth lingual face from the crested labial face of crown. Cusps are often displaced distally ( Figure 12B View FIGURE 12 2, C2 View FIGURE 2 ). The crown of cuspidate teeth are often asymmetric in occlusal view ( Figure 12B View FIGURE 12 2 View FIGURE 2 ), and the transversal keel is particularly irregular in these specimens, forming sometimes a pair of pseudo cusplets laterally ( Figure 12B View FIGURE 12 1 View FIGURE 1 ). Other teeth have a minute or no median cusp, the transversal keel being erected to low according to their position in jaw. The lateral edges of the lingual face are straight ( Figure 12A View FIGURE 12 1 View FIGURE 1 ) to concave ( Figure 12B View FIGURE 12 1, C1 View FIGURE 1 ) in lingual view, and converge toward the rounded lingual visor. The lingual face is concave, except in its median part below the cusp. The marginal angles are pointed ( Figure 12C View FIGURE 12 2 View FIGURE 2 ). The labial face is also mainly concave. It is delimited by the salient and irregular transversal keel and some secondary inner crests that sometimes merge with the previous one laterally. Most of the non cuspidate teeth have a labial face without any secondary crest, this face being rounded near the labial visor. In some antero-lateral teeth (of males?) with salient cusp ( Figure 12B View FIGURE 12 ), this merging forms a narrow basin in occlusal view ( Figure 12B View FIGURE 12 2 View FIGURE 2 ). More posterior teeth ( Figure 12C View FIGURE 12 ), holotype included, show an occlusal face more elongated mesio-distally with inner irregular crests transversally oriented ( Figure 12C View FIGURE 12 1 View FIGURE 1 ). Some minute enameloid peaks could appear along the transverse keel and near the labial visor, thereby forming sometimes rare anastomosed ridges. The lower face of the labial visor, overhanging the root, is particularly well developed ( Figure 12A View FIGURE 12 3, C3 View FIGURE 3 ), extending from one side to the other marginal angle. The root is relatively narrow compared to the crown in lingual or labial views. Several small foramina are visible on its labial face, near the crown/root junction. The root is relatively high in profile of anterior teeth ( Figure 12A View FIGURE 12 2 View FIGURE 2 ), and is lingually oriented without exceeding largely the visor. The root is of holaulacorhizous type with two lobes comparatively short and separated by a nutritive groove where one ( Figure 12A View FIGURE 12 3 View FIGURE 3 ) to several foramens ( Figure 12C View FIGURE 12 3 View FIGURE 3 ) emerge. The basal face of root lobes, which tend to converge each over, are semi-circular in basal view.
Remarks
The numerous teeth belonging to this new taxon have a variable morphology, with crowns rugose and typically asymmetric with short to minute cusp revealing a dentition assignable to the Neotrygoninae (e.g., Taeniura ) among dasyatids. For instance, Herman et al. (1999) and Cappetta (2012) abundantly figured teeth of Taeniura lymma . Monognathic and sexual heterodonties figured by Herman et al. (1999, pl. 7) are comparable to the variability observable in the KEB-1 sample, male teeth (during the breeding season) having short cusp more or less displaced laterally when female or male teeth (outside the breeding season) are less cuspidate, except along one lateral file (Herman et al., 1999, text, plate 1). However, none of the figures of Taeniura lymma shows teeth with such an irregular transverse keel nor labial face marked by numerous secondary crests that often form an inner concave basin as observable in some specimens of Mecotrygon asperodentulus nov. gen nov. sp. (e.g., Figure 12B View FIGURE 12 2 View FIGURE 2 ). However, we can note some similarities with other taxa. For instance, the irregular transverse keel of M. asperodentulus reminds that of the Ypresian “ Dasyatis” tricuspidatus Casier, 1946 , a taxon, which presents a peculiar tricuspidate transversal keel and a secondary crest on the labial crown face. Possibly reported from the Middle Eocene (Case et al., 1996, as Dasyatis sp. ) until the Priabonian (Cicimurri and Knight, 2019), “ D.” tricuspidatus is distinct from M. asperodentulus nov. gen. in having teeth with long, wide root lobes and a lingual visor more or less bifid. Neotrygonins are relatively scarce in the fossil record, especially in Middle-Late Eocene deposits of the Tethys area. Adnet et al. (2011) and Underwood et al. (2011) reported the presence of Taeniura sp. in MI, BQ, KM and QS, Egypt. The rare figurations of them (Adnet et al., 2011, from KM / Underwood et al., 2011, from BQ) are seemingly different from the KEB- 1 specimens in having a more rugose and discontinuous transversal keel. However, we do not exclude that some material attributed to the Middle Eocene Taeniura (e.g., from MI) could in fact belong to a distinct new taxa. Otherwise, the material from EG attributed to Dasyatis sp. 1 and characterized by a cuspidate crown with a cutting crest on the sides of the lingually directed cusp and a labial face without trace of enamel ornamentation (Strougo et al., 2007) belongs definitively to the new taxon (pers. observ. SA, HC). Murray et al. (2014, figure 4J) also reported the presence of Taeniura in JQ, earliest Oligocene of Fayum with a tooth that could represent a female design (or male outside the breeding season) seemingly differing from new taxa.
Specimens repositories. Holotype and Paratypes are deposited in the paleontological collections of the museum of the “ Office National des Mines ” of Tunis , 24 rue 8601, 2035 La Charguia, 1080 Tunis, Tunisia
Temporal range. Uppermost Lutetian – lowermost Bartonian ( Egypt) to middle Bartonian ( Tunisia).
Sub Family UROGYMNINAE Last et al., 2016
Genus HIMANTURA Müller and Henle, 1837
Type species. Himantura uarnak (Gmelin, 1789) View in CoL , extant species
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