Heptranchias howellii ( Reed, 1946 )

Adolfssen, Jan S. & Ward, David J., 2015, Neoselachians from the Danian (early Paleocene) of Denmark, Acta Palaeontologica Polonica 60 (2), pp. 313-338 : 319-320

Heptranchias howellii ( Reed, 1946)

Fig. 2K, L.

1890 Notidanus microdon Agassiz : Davis 1890; 380, pl. 38: 5.

1946 Notidanion howellii sp. nov.: Reed 1946; 1, figs. 1–4.

1974 Heptranchias howellii Reed ; Welton 1974, 7, pl. 2: A, B.

2006 Heptranchias howelli Reed ; Adnet 2006: 18, pl. 1: 3–8.

2008 Heptranchias howelli Reed ; Mannering and Hillier 2008: 1345, text-fig. 4A, B

2009 Heptranchias howelli Reed ; Bieńkowska-Wasiluk and Radwański 2009: 238, pl. 1: 1–5.

Material.—An almost complete lower antero-lateral tooth and an incomplete upper lateral tooth ( OESM- 10046-14, OESM- 10046-15). Two incomplete lower antero-laterals and one upper anterior specimen are kept in a private collection, all collected from the Br 2 in Faxe.

Description.—An upper lateral tooth ( Fig. 2L), labio-lingually compressed with a long and acute strongly sigmoid main cusp, with mesial serration and a distal cusplet. The root has a rounded basal edge, but it is mesially damaged so the outline is uncertain.

The lower tooth ( Fig. 2K) is strongly compressed labio-lingually with a strong triangular main cusp and six cusplets. The main cusp carries eight reduced mesial cusplets on the lower mesial face, increasing upwards in size. The first distal cusplet after the main csup is slightly lower than number two, three and four, but twice the size of number five. The sixth distal cusplet is very small. The root is tall and mesio-distally elongated with a slightly damaged basal edge.

Remarks.—The contemporaneous middle Danian Heptranchias sp. from the Limhamn quarry in Sweden ( Siverson 1995) differs from the Faxe specimen by the presence of numerous reduced mesial cusplets in the latter. Numerous mesial cusplets are also present in another tooth held in the private collection of Alice Rasmussen in Faxe ( JSA, personal observation). Since the teeth are of the same size, around 13 mm wide and appear to have been in the same position in the lower jaw, the differences can hardly be solely due to ontogeny. The tooth figured by Cappetta (1981) as H. howellii from the early Eocene of Morocco displays five poorly developed mesial cusplets, similar to the Faxe specimen. A further 10 specimens from Morocco of similar size (12–15 mm) in the DJW collection display between four and six reduced mesial cusplets, varying from poorly developed to robust. Lower Heptranchias teeth from the early Oligocene of Poland show a similar degree of variation ( Bieńkowska-Wasiluk and Radwański 2009). Clearly the number and degree of development of mesial cusplets in lower teeth is not a reliable taxonomic character. Currently Heptranchias teeth are too intraspecifically variable to identify trends or groupings in order to separate them into separate species. In the lower teeth of the Recent H. perlo the mesial face of the main cusp carries one to five cusplets ( Welton 1974) and it appears to have been the same in H. howellii ( Reed 1946; Welton 1974; Adnet 2006) and in the Heptranchias sp. described by Waldman (1971). The Danian material from New Zealand ( Mannering and Hiller 2008) is too poorly preserved for comparison.

Stratigraphic and geographic range.—Middle Danian (early Paleocene) of Denmark to early Oligocene of Poland ( Bieńkowska-Wasiluk and Radwański 2009), Danian (early Paleocene) of New Zealand ( Mannering and Hiller 2008), and the Eocene and Oligocene of Oregon, USA ( Welton 1974).