Protacrodus aequalis Ivanov, 1996

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 : 14-15

Protacrodus aequalis Ivanov, 1996

Figure 6.1

v. 1982 Protacrodus sp. ‘C’; Turner, pp. 125-126, fig. 7.

v. 1994 Protacrodus sp. C ; Ivanov and Lukševičs, pp. 25-26, fig. i, j.

v. 1996 Protacrodus aequalis sp. nov.; Ivanov, p. 423, fig. 6A-G.

v. 1999 Protacrodus aequalis Ivanov ; Ginter and Turner, p. 113, fig. 7A-C.

v. 2000 Protacrodus aequalis Ivanov ; Ginter and Ivanov, p. 339, pl. 2I.

v. 2005 Protacrodus sp. 3 ; Derycke-Khatir, pp. 64- 65, pl. VIII, fig. 8.

v. 2010 Protacrodus aequalis Ivanov ; Ginter, Hampe and Duffin, p. 87, fig. 80D, E.

v. 2011 Protacrodus aequalis Ivanov ; Ivanov and Lucas, p. 58, fig. 6A-L.

Material. One tooth from sample TS-1, Laurel Formation, Laurel Downs, Tournaisian.

Description. Tooth with a tricuspid crown, comprising a central cusp and two lateral cusps diverging at 45 degrees from the base ( Figure 6.1 ). The cusps are compressed labio-lingually, and short and wide in lingual view. The central cusp is slightly larger than the lateral cusps, which are fused at the base to the central cusp. The cusps are all ornamented with strong cristae, which converge at the cusp apices ( Figure 6.1 ). The base is bulbous with a rounded lingual extension covered by small pores. A row of small foramina occur above a slightly arched crown-base interface on the labial side.

Remarks. The symmetrical nature of the tooth is unusual in comparison to the majority of teeth attributed to this species. Typically, the crown of P. aequalis comprises cusps that are inclined to a distal side. A similar symmetrical tooth, is figured in Ivanov (1996, figure 6F) but shows a pair of lateral cusps with less distal divergence than the tooth from the Canning Basin. The symmetrical nature of this tooth suggests placement within symphyseal region of the mandible and possibly explains the low numbers recovered.

Distribution and stratigraphic range. Recorded from the early Famennian in Arctic Canada ( Ginter and Turner, 1999), middle Famennian of Latvia ( Ivanov and Lukševičs, 1994) and the late Famennian in New Mexico, USA ( Ivanov and Lucas, 2011). Within the South Urals, Russia, this species is known from the latest Famennian to early Tournaisian ( sulcata CZ ; Ivanov, 1996). In Australia, P. aequalis is known from the Famennian in Queensland ( Turner, 1982) and the Tournaisian in the Canning Basin, Western Australia. This species has also been recorded from the Tournaisian in Belgium ( Derycke-Khatir, 2005).

Figures

FIGURE 6. Protacrodont teeth from Lower Carboniferous Laurel Formation, Laurel Downs, Lennard Shelf, Canning Basin, Western Australia. 1, Protacrodus aequalis, WAM 15.6.43, sample TS-1, in lingual view (1); 2-4, Protacrodus sp. 1, WAM 15.6.45, sample TS-1, in lingual (2), occlusal (3) and labial (4) views; 5-12, Deihim mansureae, WAM 15.6.17, in lingual view (5), WAM 15.6.18, sample 198408, in occlusal view (6), WAM 15.6.46, sample TS-1, in lingual view (7), WAM 15.6.48, sample TS-1, in lingual view (8), WAM 15.6.19, sample 198404, in labio-basal view (9), WAM 15.6.17, sample 198404, in labial view (10), WAM 15.6.49, sample TS-1, in labio-basal view (11), and WAM 15.6.18, sample 198404, in lateral view (12); 13-16, Dalmehodus cf. turnerae, WAM 15.6.30, sample LG-1, in lingual (13) and labial (14) views, WAM 15.6.44, sample TS-1, in occlusal (15) and lateral (16) views. Scale bar length: 1-4, 0.5 mm; 5- 12, 1 mm; 13-16, 0.25 mm.