EUCHONDROCEPHALI Lund and Grogan, 1997

Roelofs, Brett, Barham, Milo, Mory, Arthur J. & Trinajstic, Kate, 2016, Late Devonian and Early Carboniferous chondrichthyans from the Fairfield Group, Canning Basin, Western Australia, Palaeontologia Electronica (Barking, Essex: 1987) 262, pp. 1-28 : 20

publication ID	https://doi.org/ 10.26879/583
persistent identifier	https://treatment.plazi.org/id/ED189025-607F-FF96-FF00-F8C86E7693DE
treatment provided by	Felipe
scientific name	EUCHONDROCEPHALI Lund and Grogan, 1997
status

Treatment

Subclass EUCHONDROCEPHALI Lund and Grogan, 1997

Superorder HOLOCEPHALI Bonaparte, 1831 Holocephali gen. et sp. indet.

Figure 7.14 View FIGURE 7 -17

Material. 12 teeth from 198404, two teeth from 198480, seven teeth from TS-1, Laurel Formation, Laurel Downs, Tournaisian.

Description. Large teeth up to 21 mm across the crown, mesio-distally. The crown is asymmetrical and covered in a series of minute pores ( Figure 7.14 View FIGURE 7 -15). The centre of the crown is elevated, forming a large bulbous projection with a rounded, labially directed apex that overhangs the base on the labial margin ( Figure 7.16 View FIGURE 7 -17). On one side of the main projection is a smaller one, approximately half the size and also directed labially. The other distal end of the crown is flattened with no discernible elevation. A row of well-developed cusplets is present on the baso-labial side of one incomplete tooth crown (WAM 15.6.14, Figure 7.14 View FIGURE 7 ). The boundary between the crown and base on the lingual side of the tooth is marked by a shallow groove. The base has a short lingual extension with some teeth preserving thin distal margins extending beyond the crown. A row of tightly packed canals, extending from the lingual margin to the crown base, occupy the lingual face of the base ( Figure 7.15 View FIGURE 7 ). The labial face of the base is thin and borders a shallow trough perforated by small pores. The underside of the baso-linguinal extension and majority of the crown is gently convex and smooth, devoid of foramina.

Remarks. Teeth conforming to this morphology were first documented in the Canning Basin by Thomas (1957, 1959) who published photographs of “Bradyodont” teeth from the Laurel Formation. These teeth were later redescribed by Turner (1982) who tentatively attributed them to the genus Helodus . The teeth described here and the ones previously recovered from the Laurel Formation, both share crowns perforated by tiny pores as well as a base with small, elongate canals. In addition, the labial side of the base in these teeth are also highly vascularised. The teeth described here likely represent the same species previously recovered from the Laurel Formation with differences in crown and base shape that can be attributed to the high degree of heterodonty found in “bradyodont” sharks.

There are few features present in these isolated teeth that can be used to confidently identify them to a species level. Similar teeth have been recovered in Muhua, China, and attributed to Helodus conicus Newberry and Worthen, 1866 , however no descriptive comparison to the original teeth of this species was given ( Ginter and Sun, 2007). The mesio-distally elongate teeth from the Canning Basin share a general morphology including a high midpoint to the crown with a surface covered in small pores. In contrast, the presence of a more developed bulbous projection on one side of the crown centre, tightly packed pore canals on the lingual face of the base as well as a wider labio-lingual morphology distinguishes these teeth from those of Muhua. Characters such as tubular dentine and a bulbous crown are typical of teeth assigned to the genus Helodus , however these are not genera specific. As the similarities do not appear significant enough to be included under the same genera, we have left the teeth in open nomenclature.