Galeorhinus duchaussoisi, Adnet & Cappetta, 2008

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 : 435-438

Galeorhinus duchaussoisi sp. nov.

Fig. 2A–J.

2006 Galeorhinus ? sp. nov.; Adnet 2006: 74–76, pl. 25: 1–7.

Etymology: Species named in honour of François Duchaussois, from the “Société Laonnoise et Axonaise de paléontologie”, for his contribution to paleontological research in Prémontré.

Holotype: UM−PRE 5, an upper antero−lateral tooth, ( Fig. 2E), 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.—86 teeth.

Diagnosis.—Fossil species of Galeorhinus distinguished from the majority of Galeorhinus species ( Galeorhinus louisi sp. nov. included) in having thick, medium−sized teeth up to 7 mm in total width with a combination of a series of up to 6 large, divergent distal denticles. Galeorhinus duchaussoisi sp. nov can be distinguished from the closest fossil species G. ypresiensis by its reduced or absent mesial denticles or serrations and a strong thickness of the root, even in anterior and antero−lateral rows.

Description.—The dignathic heterodonty is moderate and concerns especially the shape and size of the cusp. The holotype ( Fig. 2E) is an upper latero−anterior tooth, broader than high. The enamel is mainly smooth. The cusp is high, well individualized, distally inclined with an angle close to 45 °; its mesial cutting edge is rectilinear on the whole, slightly concave and oblique. The distal cutting edge is straight, long and oblique. The distal heel is well−developed, oblique and bears five denticles with a size which decreases distally. The distal angle (formed by the distal cutting edge of cusp and the mesial edge of the first denticle of the heel) is acute. The lingual face of the crown is rather convex transversely, especially on the median part and it sometimes bears some parallel folds at the base of the mesial extremity ( Fig. 2E 1 ). The labial face is rather convex, especially at the level of the cusp. Its basal limit is medially concave and clearly overhangs the root without forming a true transversal bulge. The root is thick; the lobes have very flat basal faces and are separated by a broad and deep nutritive groove that reaches the crown−root boundary on the lingual face ( Fig. 2E 1 ). A large foramen opens in the median part of the groove. The lingual protuberance of the root is well−marked but not salient. The two margino−lingual faces of the root show many and rather large foramina, especially towards the ends of the lobes. In lingual view, the basal edge of the root is medially concave and marginally raised. The labial face of the root is low, with a slightly concave profile and bears many foramina, irregularly spaced and aligned parallel to the basal edge. Other antero−lateral teeth show a similar morphology with moderate change in cusp shape ( Fig. 2D) and number of distal denticles.

In the anterior teeth, the mesial cutting edge of the cusp bears few serrations on its basal and median part ( Fig. 2B, C). The distal heel is abrupt and cut out by five denticles. The nutritive groove is narrower ( Fig. 2C 2) than on the holotype.

A lower symphyseal tooth is almost symmetrical ( Fig. 2A). The tooth is rather narrow, with an almost vertical erected cusp. The mesial edge is concave, with a blunt denticle in its median half part. The distal edge is very abrupt and bears three denticles; distal angle is close to 90 °. The lower boundary of the enamel is medially concave.

The lower teeth ( Fig. 2F–J) are relatively broader than the upper ones, with a more erect cusp, leading to a more concave mesial cutting edge. On an anterior tooth ( Fig. 2G), the mesial cutting edge is medially concave to slightly convex near the apex of the cusp; the distal cutting edge is long and oblique and the distal heel has three denticles. This tooth is remarkable by the presence of a broad and probably abnormal supplementary nutritive groove across the mesial lobe of root ( Fig. 2G 2). In more lateral files, the mesial cutting edge cerdo. Teeth of the Belgian G. ypresiensis ( Casier, 1946) , is more concave. The distal heel bears from three to five well−known from the Ypresian–Lutetian stages in the Engdenticles according to the tooth position. One tooth ( Fig. 2I) lish−French−Belgian basin ( Bor 1985; Dutheil 1991; Kemp shows only one denticle followed by a rather straight heel, 1994) and the U.S. Atlantic Coast ( Ward and Weist 1990; except in its distal part where it bends. The labial crown−root Kent 1999a), is related to Galeorhinus duchaussoisi sp. nov. boundary is slightly concave in the median part, except on a but despite a certain resemblance, the teeth of the new species very massive tooth ( Fig. 2F) which has a median convexity. can be easily separated from G. ypresiensis by their larger size, The root is massive and thick as in the upper teeth. their more important thickness and the usual lack of denticles Comments.—Many species have been attributed to the triakid or serrations on the mesial cutting edge from anterior to genus Galeorhinus , but, in fact, a close examination of their antero−lateral files. As the tooth morphology of G. ypresiensis dentitions show that most of them belong to the carcharhinid is relatively confused in the literature, typical teeth of G. genus Physogaleus . This is the case for the species G. cuvieri ypresiensis from Forest−lez−Bruxelles (the type locality) have (Agassiz, 1835), from the Ypresian of Monte Bolca, northern been refigured here ( Fig. 3A–C ) for comparison.

Italy (still assigned to Galeorhinus in Cappetta 2006), for the Galeorhinus duchaussoisi sp. nov. is clearly separated widespread species G. minor (Agassiz, 1835) noted in the from the other fossil species of the genus in having thick Paleocene and the Eocene from the English−French−Belgian teeth with a crown bearing numerous denticles (up to 6) on Basin ( Leriche 1905, 1906; Casier 1946, 1966; Herman 1972, the distal heel. In fact, most Paleogene species of Galeo− 1977; Ward 1980; Kemp 1994) to the East coast of the USA rhinus have teeth with no more than 3 distal denticles, as seen ( Ward and Weist 1990; Cvancara and Hoganson 1993; Case in G. mesetaensis Noubhani and Cappetta, 1997 and G. 1996) and for the species G. falconeri White, 1926 from the minutissimus (Arambourg, 1935) from Morocco. Moreover, Lutetian of Nigeria. The species G. huberiensis Case, 1981 , G. mesetaensis has teeth always bearing folds at the base of from the late Eocene of Georgia, is clearly different from all the labial face of the crown, mainly under the heels. G. the others in its large size (10 mm in width), high number of minutissimus has much smaller teeth with a more slender secondary denticles or serrations on the mesial cutting edge of cusp.

the cusp and a labio−lingually compressed root which resem− The species G. loangoensis Dartevelle and Casier, 1943 bles the morphology of the large carcharhinid genus Galeo− (pl. 12: 32–36) was described from the Lutetian of Landana, + Angola. The type series is not homogeneous and the teeth of their figs. 34 and 35, and maybe 33, can be attributed to the genus Physogaleus . Only fig. 32, depicting a symphyseal tooth, and fig. 36, which shows posterior tooth, represent the genus Galeorhinus . This material is quite insufficient to correctly define a species, but these teeth, mainly the symphyseal one, differ clearly from the teeth of G. duchaussoisi sp. nov.

Adnet (2006: pl. 25: 1–7) figured an unnamed species (as Galeorhinus ? sp. nov.) from the late Ypresian of St Géoursd’Auribat (Landes, southwestern France) which can now be assigned to the new species G. duchaussoisi .

Stratigraphic and geographic distribution.—Late Ypresian (NP12) of north and southwestern France.

Figures

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.