Squalus gabrielsoni Siverson, 1993b

Adolfssen, Jan S. & Ward, David J., 2015, Neoselachians from the Danian (early Paleocene) of Denmark, Acta Palaeontologica Polonica 60 (2), pp. 313-338 : 320-321

Squalus gabrielsoni Siverson, 1993b .

Fig. 3B–E .

1993 Squalus gabrielsoni sp. nov.; Siverson 1993b: 8, pl. 2: 1–8.

Material.—Six teeth from the Ce of Stevns Kridtbrud ( MGUH 29829, MGUH 29830, GMV 2012-60 [batch number]), two teeth and 13 fragments from the Br1 at Kulstirenden ( MGUH 29831, MGUH 29832, GMV 2012-61 [batch number]), and two teeth from the Br2 at Faxe ( GMV 2012-62).

Description.—The heterodonty in Squalidae is moderately monognathic. Monocuspid teeth show a cusp strongly declined towards the commissure and a long slightly irregular mesial cutting edge. The cusp is triangular and may be gently turned upward in males. The distal heel is long and convex, joining the cusp in a notch. The labial face of the crown is smooth and convex with median apron. The apron is elongated with parallel edges reaching well below the basal edge of the root. The lingual face of the crown is smooth with a prominent mesially twisted uvula. The labial face of the root is low, with several foramina below the crown-root junction. The basal face of the root is in general almost flat with the axial foramina fused into an infundibulum. Anteri- or and upper teeth are narrower and higher than lateral and posterior teeth. Teeth reaching up to 3 mm in width and 2 mm in height.

Remarks.—Differs from S. minor ( Leriche 1902) in having irregular cutting edges and a more demarcated apron and from S. smithi ( Herman 1982) in having an apron with almost parallel faces, whereas S. smithi has a triangular apron. S. crenatidens ( Arambourg 1952) differs from S. gabrielsoni in the shape of the apron, which is triangular in the former and the strongly serrated cutting edge of S. crenatidens . The specimens depicted as S. minor by Case (1996) from the Paleocene of New Jersey, USA resemble the Danish material

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and may be conspecific. The separation of several species of Squalus is rather difficult owing to the very conservative morphology of the genus and ontogenetic heterodonty. In particular, the shape of the apron has been used as a character for defining species within Squalidae , which itself is subject to ontogenetic variation. The use of the fusion of the axial foramina into an infundibulum is also unreliable, as this appears to be a very variable character.

Stratigraphic and geographic range.—Mid-Maastrichtian ( Siverson 1993b) to middle Danian of southern Scandinavia.

Figures

Fig. 3. Hexanchiformes, Squaliformes, and Squatiniformes from the Danian of Stevns Kridtbrud, Kulstirenden, and Faxe kalkbrud. A. Chlamydoselachus sp., MGUH 29828, DK635 (Ce) lateral tooth in labial (A 1), lingual (A 2), and distal (A 3) views. B–E. Squalus gabrielsoni Siverson, 1993. B. MGUH 29829 (Ce) lower anterior tooth in labial (B 1) and lingual (B 2) views. C. MGUH 29830 (Ce) lower lateral tooth in labial (C 1) and lingual (C 2) views. D. MGUH 29831 (Br1) lateral tooth in labial (D 1) and lingual (D 2) views. E. MGUH 29832 (Br1) lateral tooth in labial (E 1) and lingual (E 2) views. F. Squaliodalatias sp., MGUH 29833 (Ce) lateral tooth in labial view (F 1), lingual (F 2), and distal (F 3) views. G, H. Centroscymnus praecursor Müller and Schöllmann, 1989. G. MGUH 29834 (Ce) lower tooth in labial (G 1) and lingual (G 2) views. H. MGUH 29835 (Ce) lower tooth in labial (H 1) and lingual (H 2) views. I, J. Squatina sp. I. MGUH 29836 (Ce) lateral tooth in labial (I 1) and lingual (I 2) views. J. MGUH 29837 (Ce) lateral tooth in labial (J 1) and lingual (J 2) views. K. Parasquatina cappettai Herman, 1982, MGUH 29838 (Ce) tooth in labial view (K ), lingual (K ), and distal (K ) views.