Palaeobrachaelurus sp.

Kriwet, Jürgen, 2003, Neoselachian remains (Chondrichthyes, Elasmobranchii) from the Middle Jurassic of SW Germany and NW Poland, Acta Palaeontologica Polonica 48 (4), pp. 583-594 : 585-586

Palaeobrachaelurus sp.

Fig. 2C .

Material.—A single tooth (BGRX 12502), Kłęby 1/37: 244.8–245.7 m. Callovian.

Description.—The single specimen is rather small. The main cusp is bulky, upright and bent lingually with an abraded apex. The tooth crown is mesio−distally expanded and displays well−developed lateral heels with two pairs of lateral cusplets. The first pair of cusplets is distinctly separated from the main cusp. The outer lateral cusplets are only rudimentary. The labial face of the tooth crown is convex in both apico−basal and mesio−distal directions. The base of the crown overhangs the root labially with a prominent apron. The apron is broad and rectangular in labial view with divergent margino−lateral marginsand a slightly centrally concave labialmargin. The lingual face of the crown is very convex and continues into a short but broad and tongue−shaped uvula covering the lingual protuberance of the root almost completely. The occlusal surface of the uvula is flat. The crown−root junction is slightly furrowed and marked by a neck collar. The tooth crown is completely smooth without any ornamentation or sculpture.

The root is hemiaulacorhize with a central foramen that is connected to a second smaller one via a shallow canal on the surface of the root. There is a rather distinct medio−lingual foramen that opens onto the lingual face of the protuberance just below the neck collar. The root lobes are flared and jut out below the crown marginally in labial view. Lingually, they meet to form the protuberance, which is broad in basal view. The area enclosed by the root lobes is flat and of V−shaped outline. The central foramen opens into the area between the root lobes. The basal surfaces of the root lobes are flat. Two margino−lingual foramina are present on one side of the root, while there is only a single on the other.

Remarks.—The tooth from Kłęby displays all characteristic features of orectolobiform teeth (e.g., bilaterally symmetrical, overall crown morphology, hemiaulacorhize root). The morphology matches perfectly the one of teeth attributed to Palaeobrachaelurus from the Early and Middle Jurassic of Germany, Belgium, and England (e.g., Thies 1983, 1989; Delsate and Lepage 1990). The lack of any ornamentation or sculpture differentiates it easily from other contemporaneous orectolobiforms (e.g., Annea , Orectoloboides ). The dentition of Palaeobrachaelurus is slightly heterodont expressed by the presence or absence of lateral cusplets and the form of the labial apron ( Thies 1983; Cappetta 1987). The labial margin of the apron is rounded in anterior to antero−lateral files, while it is straighter or even concave in lateral to posterior rows. The cusplets are completely reduced in posterior rows. Consequently, the tooth from Kłęby comes from a lateral tooth row.

Palaeobrachaelurus is known from the Toarcian of Germany ( P. aperizosteus Thies, 1983 ) and Belgium (P. sp., Delsate and Lepage 1990), from the Aalenian of Germany (P. spp., Thies 1983), from the Bathonian of England (Charlie J. Underwood personal communication 2002), and from the Callovian of England ( P. alisonae and P. bedfordensis, Thies 1983 ). Candoni (1995) indicates the presence of Palaeobrachaelurus in the Kimmeridgian of northern France, which would represent the stratigraphic youngest record. Teeth of P. asperizosteus differ in the much more expanded crown base with four lateral cusplets in lateral teeth and a less well−developed, rectangular apron. The contemporaneous specimen from Belgium resembles teeth of P. alisonae Thies, 1983 . The main distinctive character of P. alisonae is the morphology of the crown base and the apron. The apron in P. alisonae is tongue−like with concave margino−labial margins. Lateral teeth of P. bedfordensis from the Callovian of England also differ in the morphology of the apron and in the presence of two pairs of well−developed and distinct lateral cusplets from P. alisonae . The specimens described by Thies (1989) from the Aalenian of Germany disagree in the morphology of the crown, especially of the apron, and in the form and number of lateral cusplets compared to P. alisonae . The teeth from the Bathonian of England differ in the overall morphology of the cusp and cusplets and in the form of the apron (Charlie J. Underwood personal communication 2002). The specimen from Kłęby might represent a new species of Palaeobrachaelurus . However, it seems premature to attribute it to a new or already known species since the tooth morphologies of different species are very similar and only a single tooth has been recovered from Poland so far.

Figures

Fig 2. A. Hybodontiformes indet. BGRX 12499; in lateral (A 1, A2) and occlusal (A3) views. All × 40. B. Pseudospinax? sp. BGRX 12500, Kłęby 1/37: 244.8–245.7 m, Callovian; in occlusal (B1), lateral (B2), and lingual (B3) views. All × 80. C. Palaeobrachaelurus sp. BGRX 12502, Kłęby 1/37: 244.8–245.7 m, Callovian in labial view (C1), × 55, occlusal view (C2), × 55, lateral view C3, × 55, lingual view (C4), × 55, and basal view (C5), × 40. D. Holotype of Folipistrix digitulus gen. et sp. nov. SMNS 87861, Weilen unter den Rinnen, SW Germany, Dogger α, lower Aalenian; in labial view (D1), × 50, lateral view (D2), × 50. lingual view (D3), × 45, latero−lingual view (D4), × 45, and basal view (D5), × 45.