Cretalamna deschutteri, Siversson & Lindgren & Newbrey & Cederström & Cook, 2015

Siversson, Mikael, Lindgren, Johan, Newbrey, Michael G., Cederström, Peter & Cook, Todd D., 2015, Cenomanian-Campanian (Late Cretaceous) mid-palaeolatitude sharks of Cretalamna appendiculata type, Acta Palaeontologica Polonica 60 (2), pp. 339-384 : 368-370

publication ID	https://doi.org/ 10.4202/app.2012.0137
persistent identifier	https://treatment.plazi.org/id/B63E4546-4339-FF89-FF81-FD866BC55EB1
treatment provided by	Felipe
scientific name	Cretalamna deschutteri
status	sp. nov.

Treatment

Cretalamna deschutteri sp. nov.

Fig. 18 View Fig .

Etymology: Named after Pieter De Schutter, in recognition of his work on Cenozoic elasmobranchs from Belgium and assistance in making teeth from the SECAB quarry available to us.

Type material: Holotype: lower anterior tooth, WAM 13.5.17 ( Fig. 18F View Fig ). Paratypes: WAM 13.5.13–16, 18–19 and UM-BET 6 ( Fig. 18A– E, G, H View Fig ).

Type horizon: Tourtia de Bettrechies , early Turonian, Late Cretaceous . Type locality: SECAB quarry, Bettrechies , northern France .

Material.— Type material only.

Diagnosis. —Upper and lower anterior teeth markedly enlarged. Most upper and lower lateroposterior teeth with markedly compressed cusp in labiolingual direction. Lingual protuberance of root relatively well demarcated in basal view in both upper and lower anterior teeth but wide and with poorly defined base in lateroposterior teeth. Median indentation of basal edge of root deep and U-shaped in anterior teeth but forming wide and shallow V with rounded apex in lateroposterior teeth. Lingual protuberance of root in anterior teeth broad and dome-shaped in profile view.

Description.— First upper anterior tooth file:An incomplete, 23.5 mm high tooth is assigned to the A1 position ( Fig. 18A View Fig ). The mesial cusplet is missing and the distal end of both lobes of the root is damaged. The cusp is very slightly inclined, presumably in distal direction. The labial face of the tooth is moderately convex in profile. The distal cusplet is triangular, divergent and, curiously, with an apex considerably more worn from prey manipulation than is the apex of the cusp. The base of the crown forms a prominent shelf at the crown/ root boundary. The root is markedly asymmetrical in basal view with the mesial lobe significantly more compressed than the distal lobe. The base of the lingual protuberance is well defined in basal view. The basal third of the cusp, neck and lingual protuberance of the root form a gently curved arch in profile view. The basal edge of the root is U-shaped and the mesial lobe is narrower than is the distal lobe.

Upper lateroposterior tooth files: Four teeth are referred to the inferred upper lateroposterior hollow; two from the left side of the jaw ( Fig. 18B, C View Fig ) and two from the right side ( Fig. 18E, G View Fig ). The upper left teeth are both most likely from the anterior half of the inferred upper lateroposterior hollow, whereas the two right teeth are from the posterior part of the hollow. The cusp is moderately (more anteriorly situated teeth) to strongly (posteriorly situated teeth) distally curved in labial/lingual views. It is markedly labiolingually compressed and straight (posteriorly situated teeth) to labially curved in profile view. The cusplets are large and well defined in the anteriorly situated teeth but the mesial cusplet is largely merged with the mesial cutting edge of the cusp in the two posteriorly situated teeth ( Fig. 18E View Fig 1 View Fig , G 3 View Fig ). The lingual view of the root is progressively more asymmetrical in more posteriorly situated teeth with an enlarged mesial side. The median indentation of the basal edge is wide and shallow. The basal view is very similar in all four teeth and shows a wide, very poorly demarcated protuberance and a slightly V-shaped outline of the root.

First lower anterior tooth file: One complete tooth, 19 mm high, is referred to the a1 file ( Fig. 18D View Fig ). The cusp is triangular, relatively short and erect. It is strongly lingually curved in profile view. A relatively small, triangular cusplet is situated on either side of the cusp.The root is nearly perfectly symmetrical in labial/lingual views and has rounded lobe-extremities. A low, nearly symmetrical basal view features a relatively well demarcated, broad protuberance ( Fig. 18D View Fig 2 View Fig ).

Second lower anterior tooth file: A 22 mm high tooth (holotype) is assigned to the left a2 position ( Fig. 18F View Fig ). The tooth is missing a small section of the lingual face of the root but has otherwise the best root surface preservation of all examined teeth from the SECAB quarry. The cusp is slightly distally inclined in labial/lingual views and tapers off rather abruptly in the distal third of its length. The cutting edges of the cusp are lingually curved in profile and slightly sigmoidal. A pair of divergent, triangular cusplets is present at the base of the cusp. The labial base of the crown is developed into a shelf-like structure. The asymmetrical root features a short, broad and angular distal lobe, in contrast to a more elongated, narrower and rounded mesial lobe. The base of the lingual protuberance is well-defined in basal view. In profile view, the lingual protuberance is low.

Lower lateroposterior tooth files: One tooth, 10.5 mm high, is referred to the inferred lower right lateroposterior hollow ( Fig. 18H View Fig ). The tip of the cusp is broken off and the mesial lobe of the root has sustained some damage, primarily affecting the tip of the lobe, which is more rounded that it would have been originally. A small piece of the root is also missing at the mesial base of the lingual protuberance (clearly visible in lingual view). The triangular cusp is labiolingually compressed (compared to equivalent teeth in other species of the genus) and distally inclined. It is slightly lingually curved in profile view ( Fig. 18H View Fig 2 View Fig ). The cusplets are large, relatively upright and feature a convex inner edge, shorter than the straighter outer edge. The median indentation of the basal edge is very similar to that in upper lateroposterior teeth, being wide and V-shaped with a rounded apex.

Remarks.—See the description above of C. hattini sp. nov. for a comparison of the two species. The root is taller in lingual view (relative to its width) in lower anteriors of the two coexisting species C. appendiculata ( Fig. 3A 3 View Fig ) and C. gertericorum sp. nov. ( Fig. 11F View Fig 3 View Fig ) than it is in C. deschutteri sp. nov. ( Fig. 18D View Fig 4 View Fig , F 3 View Fig ). Most lateroposterior teeth of C. gertericorum sp. nov. have a small and shallow but tightly curved median indentation of the basal edge of the root (e.g., Fig. 11C View Fig 3 View Fig ) whereas the equivalent indentation is wide and V-shaped in C. deschutteri sp. nov. ( Fig. 18B View Fig 4 View Fig ). In C. appendiculata it is deep and U-shaped in anteriorly situated upper lateroposterior teeth ( Fig. 2D View Fig 3 View Fig ). The lingual protuberance is very small and well demarcated in basal view in most lateroposterior teeth of C. gertericorum sp. nov. ( Fig. 11G View Fig 3 View Fig ) but larger and poorly demarcated from the sloping legs of the lingual edge of the root in C. deschutteri sp. nov. ( Fig. 18H View Fig 4 View Fig ). The often rectangular basal view of the root in C. gertericorum sp. nov. ( Fig. 11C View Fig 1 View Fig ) has not been observed in C. deschutteri sp. nov. In mid- to anteriorly situated upper lateroposterior teeth of C. appendiculata , the distal lobe is labiolingually compressed compared with the mesial lobe Fig. 2C View Fig 1 View Fig , D 2 View Fig ). Teeth from middle part of the inferred upper lateroposterior hollow in C. deschutteri sp. nov. ( Fig. 18B View Fig 2 View Fig ) have a rather symmetrical basal view of the root, like in C. hattini sp. nov. (Fig. 15H 1). This difference between the two taxa seems to be reversed in upper commissural teeth as the distal lobe is more compressed than is the mesial lobe in C. deschutteri sp. nov. ( Fig. 18G View Fig 1 View Fig ) and C. hattini sp. nov. Fig. 16H View Fig 2 View Fig ) whereas posteriorly situated upper lateroposteri- or teeth of C. appendiculata have a rather symmetrical root in basal view ( Fig. 2F View Fig 3 View Fig ).

The late middle to early late Turonian teeth from the Arcadia Park Formation, illustrated and described as Cretolamna woodwardi by Welton and Farish (1993) probably belong to the C. hattini -species group. The two anterior teeth illustrated (Welton and Farish 1993: 105, figs. 1, 2) might both be first upper anteriors as the difference in cusp inclination is well within the range seen in other Cretalamna (e.g., C. sarcoportheta sp. nov.). The two teeth are superficially similar to the A1s of C. catoxodon sp. nov. but the profile view of the lingual protuberance is much closer to that of C. deschutteri sp. nov. ( Fig. 18A View Fig 3 View Fig ) than it is to that of C. catoxodon sp. nov. (Fig. 20A 2). The upper lateroposterior tooth illustrated along with the two upper anterior teeth as C. woodwardi by Welton and Farish (1993: 105, figs. 1, 2) clearly differs from the corresponding teeth of C. deschutteri sp. nov. by its labiolingually thick cusp (see Fig. 18B View Fig 3 View Fig ). Teeth of the C. hattini group, very similar to those misidentified by Welton and Farish (1993) as C. woodwardi , occur in the basal part of the Fairport Member of the Carlile Shale at Mosby, Montana (MS, personal observations), indicating the presence of two coexisting species of the C. hattini group (assuming C. deschutteri sp. nov. ranges into the middle Turonian in the SECAB quarry). The North American species lacks the marked labiolingual compression of the cusp in lateroposterior files that characterises C. deschutteri sp. nov. and is in this regard closer to C. hattini sp. nov.