Cristatodens sigmoidalis, Ginter & Sun, 2007

Ginter, Michał & Sun, Yuanlin, 2007, Chondrichthyan remains from the Lower Carboniferous of Muhua, southern China, Acta Palaeontologica Polonica 52 (4), pp. 705-727 : 722

Cristatodens sigmoidalis sp. nov.

Fig. 11A–D ,?E.

Holotype: Specimen PKUM02−0165 , a tooth ( Fig. 11A ) from the MH section north of Muhua , Guizhou Province, southern China; sample MH−1, bioclastic limestone, Carboniferous , Mississippian, Tournaisian, Siphonodella crenulata conodont Zone.

Derivation of the name: Latin sigmoidalis = sigmoidal, from the outline of the crown.

Material.—Three teeth and two crowns.

Diagnosis.— Cristatodens in which the occlusal crest is sigmoidal in oral view.

Description.—The crown is composed of almost completely fused cusps; only the tips are distinguishable. The median cusp is the largest and thickest, rounded in cross section. The crest formed by the lateral cusps decreases outwards. On one side (it is difficult to determine if it is mesial or distal), it gently turns linguad, but on the other it first goes straight and at the lateral end it turns labiad. The crown is smooth save for the basal rim which is regularly crenulated. Crenulations are stronger on the labial face. The internal structure of the crown, and especially the presence or absence of the tubular dentine, is unknown.

The euselachian−type base is of the same width or only slightly wider (mesio−distally) than the crown. Its lingual margin is convex in oral view, parallel to the lingual rim of the crown. The lateral margins are straight and directed labio−lingually.

The average width of the larger teeth is 3.5–5 mm. In the smaller specimen (2.5 mm; Fig. 11D ) sigmoidality of the occlusal crest is only indistinctly marked.

There is a single, larger tooth (6.2 mm; Fig. 11E ) with a similar base shape, and the outline and crenulation of the crown, but without a differentiated median cusp and sigmoidal occlusal crest. It is only provisionally attributed here to this species.

Remarks.—The only comparable tooth from elsewhere is the specimen BMNH P.9914, from the Mississippian of Avon near Bristol, labeled as? Psephodus laevissimus ( Fig. 10B ). It is particularly similar to the tooth illustrated here in Fig. 11B , but much larger (width about 20 mm). Its crown is built of tubular dentine. It is likely that BMNH P.9914 and Cristatodens sigmoidalis are conspecific, despite the size difference, but more material is required to confirm this assumption.

Figures

Fig. 11. Teeth of Euchondrocephali incertae sedis from sample MH−1, middle Tournaisian of Muhua, China. A–D. Cristatodens sigmoidalis gen. et sp. nov. A. Holotype (PKUM02−0165) in lateral (A1), labial (A2), lingual (A3), and oral (A4) views. B. Crown of PKUM02−0166 in oral (B1) labial (B2), and lateral (B3) views. C. Crown of PKUM02−0167 in oral (C1) and lingual? (C2) views. D. Small tooth (PKUM02−0168) in lingual (D1) and oral (D2) views. E.?Cristatodens sigmoidalis, PKUM02−0169 in oblique labial (E1), oral (E2), lateral (E3), opposite lateral (E4), and lingual (E5) views.

Fig. 10. Reference specimens from Laurussia. A. Diclitodus scitulus Davis, 1883, holotype (BMNH P.49629), from the Carboniferous Limestone, Richmond, Yorkshire, England, in labial view. B. “?Psephodus laevissimus”, specimen BMNH P.9914, from the Lower Limestone shales bone bed, Avon Gorge near Bristol, in oral view. C. Chomatodus davisi (Woodward, 1889), a specimen of the type series (BMNH P.2656), from the Viséan Mountain Limestone of Armagh, Northern Ireland, in lingual view. D. Tamiobatis wachsmuthi (St. John and Worthen, 1875), a specimen of the type series (MCZ 6371), from the Kinderhookian of Burlington, Iowa, in labial view. E. Deltodus sublaevis (Agassiz, 1838), specimen BGS 5964, from the Viséan Mountain Limestone of Armagh, Northern Ireland, in oral view (left side broken). F.?Goodrichthys eskdalensis (Moy−Thomas, 1936), a tooth from the specimen NMS 2000.14.2, from the lower Viséan of Glencartholm, Dumfriesshire, Scotland, in labial view. G. Chomatodus linearis (Agassiz, 1838), specimen BMNH P.2653, from the Lower Carboniferous Yoredale Beds, Richmond, Yorkshire, England, in oral view. H. Sibyrhynchus denisoni Zangerl and Case, 1973 (FMNH PF6408), palatal tooth plates.