Chlamydoselachus sp.

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

Chlamydoselachus sp.

Fig. 3A .

Material.—A single incomplete tooth (MGUH 29828) collected in the Ce in Stevns Kridtbrud.

Description.—Tooth with three elongated cups of almost equal length. The cusps are sigmoid in lateral view and rather divergent. The median cusp is slightly inclined toward the commissure, whereas the mesial and the distal cusp are at a 45° angle with the basal face of the root. The enameloid is smooth, but may have very small wide indistinct depressions at the base of the labial face of the cusps. The cutting edges do not reach the base of the crown and the enameloid is not continuous between the cusps. Both the labial and the lingual faces of the cusps are very convex. There is no sign of strong vertical folds on the main cusps and no sign of cusplets in between the main cusps. The root is badly preserved, but appears to be wide and low and lingually reduced. A transverse notch is visible in the basal face of the root. The tooth is 24 mm wide and 14 mm high. The tooth is probably a lateral tooth, as lateral teeth have divergent cusps, whereas anterior teeth have less divergent and more erect cusps ( Pfeil 1983).

Remarks.—Fossil frilled sharks are poorly known, owing to the rarity of deep-water sediments where teeth can be recovered. However, owing to their unique morphology they are more likely to be described and figured than a lamniform tooth. Specimens are known from Antarctica ( Richter and Ward 1990), Africa ( Antunes and Cappetta 2002), Asia Goto and Research 2004), New Zealand ( Consoli 2009), North America ( Welton 1979), and Europe ( Davis 1887; Pfeil 1983; Adnet 2006; Fulgosi et al. 2009). The oldest known specimens are from the Campanian of Antarctica and Angola. Three different species were described from Angola by Antunes and Cappetta (2002) of which one species, C. gracilis , appears to be similar to Chlamydoselachus , whereas C. goliath is more reminiscent of the genus Proteothrinax ( Pfeil 2012) . The two genera were separated by Pfeil

(1983) on the lack of intermediate cusplets between the main cusps, size and being less lingually inclined. Richter and Ward (1990) argued that differences between Thrinax (Proteothrinax) and Chlamydoselachus were within the variation of Chlamydoselachus and regarded it as a junior synonym of Chlamydoselachus . Both the first discovered fossil Chlamydoselachus ( Lawley 1876) as well as C. gracilis described by Antunes and Cappetta (2002) and C. tatere ( Consoli 2009) may lack intermediate cusplets and the lingual projection of the root appears to vary. This makes the basis for a separation into two genera quite unreliable. As specimens described as Proteothrinax may just be older and larger individuals of a sturdy Chlamydoselachus species, this is more a question of ontogenetic heterodonty than of different genera.

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.