Lee Creek Rhinoptera Teeth

There appears to be two variations which are best differentiated by the nature of the longitudinal (apico-basal) ridges of the labial and lingual faces of the crown. When this page was first published, the two tooth-designs were referred to as types "R" and "S"; it is now concluded that these differences represent differing upper and lower tooth-designs.

Type "R" -- Rhinoptera sp. -- Uppers (Fig. )
Although only represented by smaller, isolated teeth, these are by far the most common ray teeth found when surface collecting the mine. When I first started collecting at Aurora, I perceived them as index fossils. When I came across one, it meant that 'real' fossils were likely in that area.
Crowns. The crowns are clearly hexagonal in shape and may be slightly to strongly elongated depending on tooth position. The height of each lateral end is relatively similar, and any observed slope extends from one end to the other. The variable width-to-depth ratios manifested by the teeth of this family often allow for easy identification (as to genus). The middle region of the labial crown face projects labially, in tenon-fashion, and fits into a depression (mortise) on the lingual face of its anterior counterpart. These interlocking faces have weak apico-basal grooves or ridges which clearly distinguish these teeth from the myliobatids.
Roots. When viewed laterally, the loblets are generally centered relative to the root stem, extending slightly to the front and back and not reaching the lingual edge of the crown. In addition, the labial edge of the loblets is generally perpendicular to the base of the crown, lacking the strong slant associated with the myliobatids. The lingual face of the root stem generally lacks foramina; the basal face usually reveals a few, and the labial face has numerous foramina above the loblets and just below the crown's overhang. Certain lower teeth, when viewed basally, have loblets which are oriented at an angle that is not perpendicular to the face of the crown, a characteristic of some Rhinoptera lateral teeth (fig. ).

Type "S" -- Rhinoptera sp. -- Lowers (Fig. )
These teeth are similar to Type "R" in overall design, but have crowns and roots which differ significantly enough to be included as a unique tooth-design.
Crowns. The labial face is more upright, lessening the tenon and mortise design so apparent in Type "R". The weakening of this crown interlocking mechanism has been compensated for by the stronger and more angular apico-basal ridges and grooves of each face -- an improved suture design. The labial face of each tooth is now positioned over the adjoining tooth's lingual ledge.
Roots. The roots, particularly the loblets, have also changed. They are now positioned to the rear and extended to the lingual margin of the collar. The labial face of each loblet has a slight depression to accommodate the loblets of their anterior counterpart.

Selected References