Dalmehodus cf. turnerae

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 : 17

Dalmehodus cf. turnerae

Figure 6.13 -16

Material. Seven teeth from sample LG-1, 11 teeth from sample 198404 and two teeth from TS-1, Laurel Formation, Laurel Downs, Tournaisian.

Description. Mesio-distally elongated teeth with slightly arched crowns comprising a low central cusp and between two and four almost completely fused lateral cusps that decrease in size distally ( Figure 6.13 -14). The central cusp varies from equal in size to slightly larger than the first pair of lateral cusps. Cusps are ornamented with faint to strong cristae ( Figure 6.14, 6.16 ). The base is roughly rectangular, extending lingually, and barely developed beyond the crown distally ( Figure 6.15 - 16). A row of large furrows are present along the lingual face of the base and extend from the lingual margin of the base to the crown base interface. The labial face of the base is small with a few small pores. The underside of the base is concave below the crown and flattened on the underside of the baso-lingual extension.

Remarks. The teeth resemble those previously attributed to Dalmehodus turnerae Long and Hairapetian, 2000 , in they possess a low, mesio-distally elongate crown covered in coarse cristae and a lingually short base with a row of rather large foramina. A key feature distinguishing teeth of D. turnerae from other protacrodonts is the lack of a discernible size difference between the central and lateral cusps. Typically, the teeth from the Canning Basin bear a central cusp slightly larger than the lateral cusps. Teeth with highly fused cusps figured in Ginter et al. (2011, text-figure 10H) and those in Hairapetian and Ginter (2009, text-figure 4B) most closely resemble the teeth from the Canning Basin and these were attributed to D. turnerae . Despite the large number of teeth from the Tournaisian deposits, the variation in morphology is limited. Teeth resembling the holotype ( Long and Hairapetian, 2000, figure 6f) and other specimens ( Hairapetian and Ginter, 2009, text-figure 9A-B) with less fusing of the cusps have not been found in samples from the Canning Basin. It may be that the teeth found here, as well as similar forms in Iran ( Hairapetian and Ginter, 2009) and Armenia ( Ginter et al., 2011), represent different protacrodont species.

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.