Galeorhinus louisi, Adnet & Cappetta, 2008
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publication ID |
https://doi.org/ 10.4202/app.2008.0306 |
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persistent identifier |
https://treatment.plazi.org/id/03DBAF0C-FFB7-EE47-FCD8-F9BBD562FCDE |
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treatment provided by |
Felipe |
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scientific name |
Galeorhinus louisi |
| status |
sp. nov. |
Galeorhinus louisi sp. nov.
Fig. 4A–F View Fig .
Etymology: Species named in honour of Pierre Louis from the local “Société Laonnoise et Axonaise de paléontologie” for his contribution to palaeontological research in the Reims region.
Holotype: UM−PRE 11, a lower antero−lateral tooth ( Fig. 4A View Fig ) collected by HC.
Type locality: Prémontré Abbey, Prémontré (Aisne, northern France).
Type horizon: “Sables de Glennes” (Laon Clays Fm.), Level 2, late Ypresian (NP12), Eocene.
Material.—Nine teeth.
Diagnosis.—Small species of Galeorhinus , teeth up to 2.2 mm in total width, with a reduced number of denticles on the distal edge of crown (up to 4) and lacking denticles and serrations on the mesial cutting edge, except sometimes a very small basal one. G. louisi differs from all other Galeorhinus species in having the base of the labial face of the crown (overhanging the labial crown−root junction) with several marked irregular folds and associated notches on the entire width, forming sometimes a horizontal, straight transversal bulge in labial view. Root not very thick, with lobes always clearly separated, even in the anterior files.
Description.—The holotype ( Fig. 4A View Fig ) is a lower antero−lateral tooth. The cusp is acute, well individualized, and distally inclined with an angle close to 45 °. Its mesial cutting edge is sigmoid, slightly convex at the base to concave near the apex. The distal edge of the cusp is short, very oblique and convex. The distal heel is abrupt and bears three large denticles. The labial crown−root boundary is concave in labial view. The basal edge of the crown, overhanging the crown−root junction, is deeply incised by several vertical notches and folds on its entire width. Limited in height, these delimit a horizontal, straight and salient bulge. In apical view ( Fig. 4A View Fig 2), the labial face is convex under the cusp and concave at its extremities, especially under the distal heel. The enamel of the lingual face of the crown is smooth. The root is moderately thick; its lobes have flat basal faces and are separated by a deep and large nutritive groove ( Fig. 4A View Fig 3 View Fig ). The margino−lingual faces of the root are well−separated from the basal face and bear some elliptic foramina on their surface. The large principal foramen opens in the lingual part of the nutritive groove. The labial face of the root is low; its profile is concave and largely overhung by the crown enamel in occlusal view ( Fig. 4A View Fig 2).
The lateral teeth ( Fig. 4C–E View Fig ) show a cusp with a more buckled enamel compared to the anterior ones, especially on the lingual face. The distal heel bears from one to three denticles. The labial crown−root boundary is generally straight and its basal transversal bulge may be very prominent and irregular, showing many folds and associated notches except on its mesial extremity ( Fig. 4B View Fig 1, C 1 View Fig ). In some more lateral files ( Fig. 4E View Fig ), the cusp is distally elongated with an apex being above the distal extremity of the root. The mesial cutting edge is long, slightly but regularly convex, with an unique small mesial serration. The distal heel is short and bears only two denticles. The labial crown−root boundary is medially concave.
A probably upper anterior tooth ( Fig. 4B View Fig ) appears less mesio−distally developed than the lower teeth. The mesial cutting edge of the crown is straight and the labial transversal bulge is medially underlined by many short and vertical folds. On the upper lateral tooth ( Fig. 4E View Fig ), the diagnosic labial transversal bulge is always developed and folded.
Comments.—The tooth morphology is definitily that of Galeorhinus but the shape of the peculiar labial crown−root boundary recalls that of a contemporaneous species such as Triakis wardi Cappetta, 1976 and justifies the description of this new species. The closest species seems to be G. mesetaensis Noubhani and Cappetta, 1997 from the Thanetian of Morocco. Yet, G. louisi sp. nov. can be clearly separated from the latter in having a more continuous and irregular bulge at the base of the labial face of the crown. Compared with G. mesetaensis , this basal bulge is lacking in the median part of the crown.
Musick et al. (2004) discussed the historical zoogeography of Galeorhinus and noted that the origin and paleoenvironment of the ancestors of the unique living species G. galeus (Linnaeus, 1758) , worldwide distributed, suggest similar thermal preferences to the cold waters as for the extant species ( Compagno et al. 2005). However, Paleogene fossil localities of North Atlantic where numerous species of Galeorhinus are recorded (such as G. louisi sp. nov.) correspond to warm climatic conditions, implying an obvious environmental change in the Recent distribution of this genus.
Stratigraphic and geographic distribution.—Late Ypresian (NP12), known only from the type locality.
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