Synechodus faxensis ( Davis, 1890 )

Adolfssen, Jan S. & Ward, David J., 2015, Neoselachians from the Danian (early Paleocene) of Denmark, Acta Palaeontologica Polonica 60 (2), pp. 313-338 : 315-316

Synechodus faxensis ( Davis, 1890)

Fig. 2A–C.

1890 Odontaspis faxensis sp. nov.; Davis 1890: 390, pl. 38: 26.

1929 Synechodus faxensis (Davis) ; Leriche 1929: 232.

1976 Synechodus hesbayensis (Davis) ; Glickman 1976: pl. 21: 19, 20, 34.

1977 Synechodus faxensis (Davis) ; Herman 1977: 36, pl. 1: 9.

Material.—One complete tooth from a juvenile (OESM-10046-17) and two incomplete teeth (MGUH 1401, OESM-10046-16) including the specimen depicted by Davis (1890) of the species from the Br 2 in Faxe. A dozen more in private collections have been studied.

Description.—Teeth with a tall main cusp and two to four pairs of lateral cusplets on the deflecting shoulders. The main cusp has smooth labial and lingual faces, whereas the cusplets may carry a few irregular vertical folds on both faces. The cutting edge appears to be continuous and strong. The base of the crown overhangs the root and displays a strong concave indentation in anterior teeth but less so in laterals and posteriors. The labial face is convex and the lingual face is strongly so. Neither of the adult specimens has completely preserved roots, but the remnants of the roots exhibit a pseudopolyaulacorhize vascularization (Herman 1977). Juveniles have much coarser vertical folds on both the labial and lingual faces, with the folds covering the lower two thirds of the labial face and almost all of the lingual face.

Remarks.— Davis (1890) described this species as being smooth on both faces. This is incorrect, as the specimen depicted by Davis (1890: pl. 38: 26) does show weak folds on both faces. Anterior teeth may have fewer folds than observed in lateral teeth and the folds become weaker in larger specimens. Leriche (1927) commented that he has no doubt that the specimens from the Maastrichtian of Belgium and the Netherlands were the same species as Davis’ (1890) tooth from Faxe.

Ward (2010) synonymised two mid-Cretaceous species of Synechodus , S. nitidus (Woodward, 1911) and S. tenuis Woodward, 1889 ), with S. dubrisiensis (Mackie, 1863) . This species has a similar distribution of folds as S. faxensis , that is anterior and presumed lower teeth display less folding.

The poorly known mid-Paleocene species Synechodus hesbayensis ( Casier 1943) , listed erroneously by Cappetta 2006: 105) as a junior synonym of Paraorthacodus eocaenus Leriche 1902 ), differs from S. faxensis in having more developed vertical ridges on the labial crown face. Further study may demonstrate that this is a positional or ontogenetically variable feature and that S. faxensis is the senior synonym.

Stratigraphic and geographic range.—Late Maastrichtian of Denmark and the Netherlands to the Thanetian of the Urals Herman 1977; Glickman 1957).