Following are the comments specific to teeth recovered from the Nanjemoy sediments of Potapaco Bed B and written prior to reading Cappetta (1986).
Making identification difficult is the condition of complete specimens. To the author's knowledge, no complete (or partial) plates have been found; leaving only shed teeth to be evaluated. By virtue of its grinding nature and strong interlocking, the teeth of this species show extreme occlusal wear (including the labial face). Fortunately, the Folmer collection includes not only what appear to be lateral teeth but fragmentary medials as well. Using a complete specimen (Fig. a), a fragmentary medial (Fig. ) and an isolated lateral (Fig. ), a reconstruction was made of the general tooth-design (Fig. b).
The few specimens available for study have a relatively level lingual crown base and roots that are deeper medially. It is currently unknown if these represent upper teeth only, or if both dentitions have similar characteristics. The upper root bears low, broad and short meandering ridges on the lingual and lateral faces. The upper crown face is ornamented with small enameloid projections, undoubtedly associated with interlocking. [Cappetta's description notes that when viewed occlusally, the upper teeth are rectilinear and the lowers curved (convex labially). Viewed labially, the crown of the uppers is deeper medially and the root lobes of equal size. In the lowers, the occlusal surface is relatively flat and the lobes higher medially.]
The large isolated lateral tooth in Figure has dramatically deep and lingually directed roots. The occlusal profile, lateral face of the crown & more strikingly the roots, compare well with those of the medial teeth in figure and .
Another of the mystery myliobatid teeth is illustrated in Figure . Kent (1999) deemed this tooth-design to be Aetomylaeus. The dentition of the fossil species A. meridionalis includes no teeth of this type, but the genus includes three or four extant species, and the author is not familiar with most.
These teeth are often small with low width:depth ratios, and usually quite worn. When casually viewed the roots look pointed from an occlusal or lingual perspective. Actually, two similar designs are present in the fauna. The more common has smooth labial and lingual crown faces and a centered marginal angle. The other has small projections (interlocking) on the crown faces, and the marginal angle is off set.
Based on the normally small size, I originally suspected them to represent neonate/juvenile examples of "Myliobatis" dixoni. teeth. However this was proved incorrect when Mike McCloskey provided a 25 mm (3:1) and Daryl Serafin a 36 mm (4:1) specimen.
Although the Eocene teeth and mouthplates could be grouped by odontological design, placing them in described taxa required an indepth knowledge of these species. I need to thank David Ward for taking the time to confirm the identificaton of "Myliobatis" latidens and providing the proper identifications for the specimens presented above as "M." sulcidens, "M." toliapicus, "M." dixoni and cf "M." nzadinensis. Henri Cappetta was kind enough to provide additional details on Pseudaetobatus and respond to a cross-examination on various details.