Aetomylaeus undetermined

Cicimurri, David J. & Knight, James L., 2019, Late Eocene (Priabonian) elasmobranchs from the Dry Branch Formation (Barnwell Group) of Aiken County, South Carolina, USA, PaleoBios 36, pp. 1-31 : 19

AETOMYLAEUS SP.

( FIG. 7A–E )

Material examined —SC96.97.49, 17 incomplete median teeth; SC96.97.50, lateral tooth; SC96.97.51, lateral tooth; SC 2001.1.1, eight partial median teeth; SC 2001.1.2, incomplete median tooth; SC 2001.1.29, lateral tooth; SC 2001.1.30, three lateral teeth; SC 2001.1.31, two incomplete median teeth; SC2001.1.32, five partial median teeth; SC2013.38.80, partial median tooth; SC2013.38.81, two incomplete median teeth; SC2013.38.82, four incomplete median teeth; SC2013.38.83, two lateral teeth.

Remarks —These 48 teeth are distinguished by their thick crowns with slightly lingually inclined labial and lingual faces. The labial face appears highly pitted ( Fig. 7A ), whereas the lingual face has a granular texture and a very thin and sharp transverse ridge is located at the crown-root junction ( Fig. 7B ). Upper median teeth can be distinguished from those in the lower dentition in being more convex overall, with a straight to curved crown base that parallels the occlusal surface. In contrast, lower median teeth have a straight crown with flat occlusal surface, and the crown foot is parallel to the basal root face. Lateral teeth are longer than wide and bear labial pitting and lingual tuberculation on crown faces ( Fig. 7D, E ).

The Dry Branch material appears to be conspecific with a myliobatoid occurring in the Clinchfield Formation of central Georgia (DJC unpublished data). In terms of overall morphology, this taxon compares quite favorably to Miocene teeth Cappetta (1970) identified as Pteromylaeus Garman, 1913 , and to Myliobatis meridionalis ( Gervais, 1852) . Cappetta (2006) synonymized M. meridionalis with Pteromylaeus , and earlier Cappetta (1987:171) considered the possibility that the material he described in 1970 could represent old individuals of Aetomylaeus . Hovestadt and Hovestadt-Euler (1999) noted the difficulty of identifying isolated fossil myliobatidae teeth and stated that Pteromylaeus is only known from extant species. However, Hovestadt and Hovestadt-Euler (2013) later assigned several fossil species previously identified as Myliobatis to Pteromylaeus and Aetomylaeus , thereby extending the record of the latter genera back into the Eocene. White (2014) more recently synonymized Pteromylaeus with Aetomylaeus , and the latter generic name is applied to the Dry Branch sample listed above.

Figures

Figure 7. Myliobatidae teeth from the Dry Branch Formation (Priabonian) of Aiken County, South Carolina. A–E. Aetomylaeus sp. Incomplete lower median tooth in labial (A), lingual (B), and occlusal (C) and views, SC2001.1.2. Lateral tooth in occlusal (D) and profile (E) views, SC2001.1.29. F–I. Pseudaetobatus undulatus. Upper median tooth in occlusal (F) view, SC2013.38.86. Lower median tooth in occlusal (G) view, SC2013.38.84. Upper right distal-most lateral tooth in occlusal (H) and labial (I) views, SC2013.38.91. Lateral tooth in occlusal (J) view, SC2013.38.96.2. K–R. Rhinoptera sp. Lateral tooth in labial (K), lingual (L), occlusal (M), and basal (N) views, SC2001.1.12. Median tooth in occlusal (O), lingual (P), and basal (Q) views, SC2001.1.16. Lateral tooth in lingual (R) view, SC2013.38.70. Labial at top in C, D, F–H, J, M–O, Q; at right in E. Scale bars=1 cm in A–C, F–I, K–R; 5 mm in D, E, J.