Stegostoma tethysiensis, 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/328467AB-1AFC-4825-BF60-65628BA4AF05 |
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taxon LSID |
lsid:zoobank.org:act:328467AB-1AFC-4825-BF60-65628BA4AF05 |
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treatment provided by |
Felipe |
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scientific name |
Stegostoma tethysiensis |
| status |
sp. nov. |
Stegostoma tethysiensis nov. sp.
Figure 8 View FIGURE 8 D-G
zoobank.org/ 328467AB-1AFC-4825-BF60-65628BA4AF05
2007 Chiloscyllium sp. 2 ; Strougo et al., p. 88-94, pl.
1, fig. 6.
2011? Stegostoma sp. ; Underwood et al., p. 52-62, fig. 6C-D.
2016 Stegostoma sp. ; Merzeraud et al., p. 14-15, tab. 1.
Etymology. Derived from the “Tethys” sea where the species inhabited.
Type locality and stratum. KEB 1-147, Figure 8D View FIGURE 8 from the KEB- 1 locality, Souar-Fortuna formations in Djebel el Kébar, Tunisia.
Other material. Additional material, including figured KEB 1-148 to 1-150 ( Figure 8 View FIGURE 8 E-G), consists of 20 teeth from the KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia.
Diagnosis. Extinct species of Stegostoma only known by isolated teeth that are characterized, compared to those of the unique and living species S. fasciatum , by teeth slightly lower and showing a light but gradual monognathic heterodonty; a pair of lateral cusplets that are more separated from the main cusp, especially in anterior files.
Description
The holotype ( Figure 8D View FIGURE 8 ) is an anterior tooth which measures 1.7 mm mesiodistally. The tooth is quite symmetrical; the crown, relatively slender, bears a sharply-pointed main cusp, which is slightly angled distally. The main cusp is flanked by a pair of lateral cusplets. The latter are strong, high, erected and well-individualized from the main cusp. The height of the mesial cusplet is about 70% of that of the main cusp, whereas the distal lateral cusplet is only about 60%. Both lateral cusplets are similarly sharply pointed and all of the cusps possess sharp cutting edges, which descend the lateral margins of the cusp mesially and distally. The lateral cusplets are sub-parallel to the main cusp. In profile, the cusplets are slightly flattened labio-lingually, as the main cusp. A moderate bifid apron is developed on the crown margin, beneath the central cusp base, and substantially overhangs the root ( Figure 8D View FIGURE 8 1 View FIGURE 1 ). The enameloid of the crown is entirely smooth. A short uvula is developed on the lingual face, above the median protuberance of the root, which is marked by a small collar ( Figure 8D View FIGURE 8 2 View FIGURE 2 ). The root has a V-shaped basal surface ( Figure 8D View FIGURE 8 3 View FIGURE 3 ), and an oval lingual foramen is present beneath the uvula. The lateral foramina are sometimes present under the crown-root boundary ( Figure 8D View FIGURE 8 2 View FIGURE 2 ). The mesial and distal lobes of the root are fine and extend slightly beyond the mesial and distal heels of the crown. A large basal nutritive foramen opens on the basal face, in the large notch built by two root lobes ( Figure 8D View FIGURE 8 3 View FIGURE 3 ).
Several antero-lateral to lateral teeth show less prominent labial aprons with much straighter labial margins and less marked overhanging of the root ( Figure 8 View FIGURE 8 E-F). The base of the central cusp is somewhat inflated mesiodistally. In some specimens, the pair of lateral cusplets may be less prominent ( Figure 8F View FIGURE 8 ) or quite similar ( Figure 8E View FIGURE 8 ) with respect to the condition found in the holotype. In both cases, one cusplet is always lesser developed than the other, either on the mesial or on the distal side. More lateral teeth ( Figure 8G View FIGURE 8 ) have a much squatter, triangular, shorter main cusp than in anterior teeth. The mesial and distal cutting edges are nevertheless consistently and strongly developed. The main cusp is also flanked by a pair of lateral cusplets, which are much shorter and possess a less acuminate, more rounded outline than is the case in more anterior teeth. The labial apron is here rounded in labial view ( Figure 8G View FIGURE 8 ). There is clearly a light gradual monognathic heterodonty between the anterior and lateral teeth of this new species. Changes taking place distally through the dentition include a gradual asymmetry of teeth, with posterior teeth slightly bended distally ( Figure 8E, G View FIGURE 8 ); a long, slender main cusp flanked by a pair of high lateral cusplets in anterior teeth generates a more squat, triangular central cusp flanked by relatively shorter, more rounded lateral cusplets in lateral teeth; a labial apron, although quite variable, regardless of the tooth position, that tends to be more bifid in anterior teeth ( Figure 8D View FIGURE 8 ) and more rounded in lateral teeth ( Figure 8G View FIGURE 8 ).
Remarks
Only known in the fossil record by Eocene teeth from Antarctica (Long, 1992) and recently revised and placed within the Hemiscylliidae (Engelbrecht et al., 2016) , the genus Stegostoma is rarely cited in the paleontological literature, unlike some specimens from the Eocene of Northern Africa belonging to this genus (Cappetta, 2012, p. 168). Contrary to most orectolobiforms ( Hemiscylliidae included), there is no well-marked heterodonty in jaws of the living representative S. fasciatum , as illustrated by Herman et al. (1992). Upper and lower teeth are virtually similar (even in the same jaw), and anterior and posterior teeth share a similar crown pattern with long symmetrical cusp and pair of cusplets. Engelbrecht et al. (2016) erected the new genus Notoramphoscyllium from supplementary material formerly attributed to Stegostoma cf. fasciatum by Long (1992) due to the presence on their new large sample of teeth with a marked gradient of monognathic heterodonty, an asymmetrical main cusp with low and also asymmetrical lateral cusplets. With this suite of characters, the latter authors assigned Notoramphoscyllium to the family Hemiscylliidae because of their general resemblance with the teeth of Chiloscyllium / Hemiscyllium , in which the monognathic heterodonty is particularly noticeable. The KEB-1 material shows symmetrical anterior teeth ( Figure 7D View FIGURE 7 ) as well as asymmetrical lateral teeth with sometimes reduced cusplets in posterior teeth ( Figure 7G View FIGURE 7 ), a feature that is seemingly inconsistent with an attribution to Stegostoma . However, and contrary to what is observed in all recent and fossil species of hemiscyllids, the lateral cusplets are always present and usually well-developed, even in the most posterior teeth. If the gradual and light monognathic heterodonty observed in the KEB-1 material recalls that of some brachaelurid taxa (e.g., Brachaelurus , Eostegostoma ), the latter are clearly distinguishable by their teeth that have a rounded and elongated apron, which overlaps the root. The genus was nevertheless previously reported in Priabonian deposits of Egypt, from the upper GE, BQ to lower QS (? Stegostoma sp. , Underwood et al., 2011), and the figured tooth (Underwood et al., 2011, figure 6C-D from BQ) appears to be similar to lateral teeth of Stegostoma tethysiensis nov. sp. We also corroborate its occurrence in EG (pers. observ. SA, HC) even if affiliated material only consists of rare broken teeth without root, except those figured by Strougo et al. (2007, plate 1, figure 6) as Chiloscyllium sp. 2 .
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), and possibly up to Priabonian ( Egypt).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.