Mustelus, Linck, 1790

Adnet, Sylvain & Cappetta, Henri, 2008, New fossil triakid sharks from the early Eocene of Prémontré, France, and comments on fossil record of the family, Acta Palaeontologica Polonica 53 (3), pp. 433-448 : 440

Mustelus aff. M. vanderhoefti Herman, 1982

Fig. 6A .

2006 Mustelus sp. ; Adnet 2006: 76–78: pl. 26: 1–3.

Material.—Two teeth.

Description.—The species of this genus are characterised by a crushing−type dentition. The lateral tooth figured here ( Fig. 6A ) is slightly asymmetrical and transversely elongated, with a reduced, distally directed cusp. The enamel of the crown is strongly wrinkled, especially on the labial and lingual faces. The crown is as high as the root. Its occlusal face is flat and relatively smooth except on its labial edge, where it bears deep folds. The labial face of the crown broadly overhangs the root in profile ( Fig. 6A 2) and the lingual face bears a salient uvula located under the cusp ( Fig. 6A 1 , A 3 ). The root is thick with a flat basal face. The lingual protuberance of the root is well−developed under the uvula and several marginal foramina open on both sides. The nutritive groove is broad, straight and the principal nutritive foramen opens on it lingual edge.

Comments.—The fossil record of the genus Mustelus is poorly documented. The oldest record seems to be from the Thanetian of the Paris Basin ( Bault and Genault 1995) but this genus remains scarce in deposits until the Neogene, during which it becomes more abundant ( Herman 1982: 191; Bault and Genault 1995: 207). Mustelus is currently one of the most diverse triakid genera, including 22 living species, and inhabits mainly the neritic zone (up to 200 m depth) of the cold to tropical areas of most of the seas and oceans (e.g., Compagno 1984; Compagno et al. 2005). The tooth morphology of Mustelus species is very homogeneous and species are hardly differentiable on the basis of dental characters ( Herman et al. 1988, 1990), which partly explains why paleontologists hesitate to refer fossil Mustelus teeth to precise species ( Cappetta and Cavallo 2006). As a result, only three fossil species of Mustelus have been described and considered as valid (Cappetta 2006): Mustelus biddlei Bault and Genault, 1995 (Thanetian of Ressons−sur−Matz, northern France); Mustelus whitei Cappetta, 1976 (lower Ypresian of Burnham−on Crouch, London Clay, England) and Mustelus vanderhoefti Herman, 1982 (Ypresian of Egem, Belgium). The teeth of Premontré, like those from the middle Lutetian of southwestern France ( Adnet 2006), are closely similar to those of Mustelus vanderhoefti , known until the middle Eocene of England ( Kemp 1994).

Figures

Fig. 6. Triakid shark Mustelus aff. M. vanderhoefti Herman, 1982. Prémontré Abbey, late Ypresian.UM−PRE 18, lateral tooth, lingual face (A), profile view (B), occlusal face (C), and basal face (D).

Fig. 1. A. Location of the Prémontré Abbey (Aisne, northern France). B. Simplified stratigraphic column of Prémontré with fossiliferous (2–3) and non−fossiliferous (4–12) levels (from Dégrémont et al. 1985: 12).

Fig. 3. Triakid shark Galeorhinus ypresiensis (Casier, 1946). Forest−lez−Bruxelles, Belgique. A. UM−FLB 1, anterior tooth, lingual face. B. UM−FLB 2, anterior tooth, labial (B1) and lingual (B2) faces. C. UM−FLB 3, anterior tooth, labial (C1) and lingual (C2) faces.