Teeth of varying genera and even families have been dumped over the years into the genus Myliobatis -- some 150 fossil species according to Cappetta (1987). It is likely that most of the species are invalid and that more than one genus is represented. The living genera as provided by Compagno (1999) include:
Myliobatis
The most common myliobatid genus used by paleontologists for the last 150 years is Myliobatis -- one could spend a decade attempting to track down type specimens and reconciling taxa assigned to this paleo-bucket. It has been abused to such an extent with Paleogene taxa that I felt compelled to place all determinations in quotes on the website. As it relates to the western Atlantic, Myliobatis was undoubtedly present during the Neogene. Hovestadt-Euler and Hovestadt (pers. com. 2007) notes that the toothplate-designs of extant Myliobatis species and those of Aetomylaeus are so variable yet similar that there is no reliable characteristic to differentiate these taxa. As Aetomylaeus is an Indo-Pacific genus, it will be assumed that it is not present in the Neogene of the western North Atlantic and that specimens falling into this tooth-design envelope are Myliobatis.
In general terms, the dentition has a laterally expanded medial file and three or four lateral files on each side. The upper and lower toothplates are of similar width, but the upper is more dorso-ventrally curved when viewed laterally. Successive rows are interlocked and teeth tend to be severely abraded when shed. Root laminae are lingually-directed and the labial crown face extends well beyond the roots (to rest on a labial ledge of the younger tooth). Myliobatis teeth can be differentiated from those of Pteromylaeus by the lateral elongation of the crown; the width to depth ratio in Myliobatis teeth tends to be 4-5 to one while in Pteromylaeus it is closer to 7-8 to one. In addition, Pteromylaeus roots tend to be more lingually extended.
With so many variables and unknowns, it would be foolish to ascribe these teeth to a particular species. With that said, Yorktown (Pliocene) specimens likely represent M. ferminvillii LESUEUR, 1824. Purdy et al (2001) did not include Myliobatis in the Lee Creek fauna.
Pteromylaeus
The dental configuration includes one elongated medial file and one or more lateral files (generally three), which may be either labio-lingually or laterally elongated. on each side. In 1996, Bob Purdy (Smithsonian) suggested the presence of Pteromylaeus at Aurora. Using Stehmann's (1981) illustrated P. bovinus toothplate certain isolated teeth (fig. ) were identified on this basis.
At that time (1996), other Lee Creek toothplates with posterio-anteriorly elongated medial files (fig. ) better compared with Aetomylaeus meridionalis as depicted by Cappetta (1987; 171, fig. 144c).
Herman et al (2000) published their myliobatid paper which more fully defined the dentition-designs of the myliobatids.
Three of these authors, Herman, Hovestadt-Euler and Hovestadt (pers. com. 2007) identified figure and/or dentition-designs as Pteromylaeus.
The crowns of the medial teeth are hexagonally shaped and the marginal angles are centered and acute, forming an elongated point. In lateral view, the labial crown face may be relatively flat (fig. a) or convex (fig. b) which likely represents the difference between the lower (less curved) and upper tooth-designs. A small tenon/mortise joint is located low on the crown, and there are meandering, apico-basally oriented wrinkles which interlock the adjoining crown faces. The width:depth ratio of the medial crown is generally seven or eight-to-one.
The roots are lingually directed, particularly the slope of the labial and lingual faces of the laminae. Foramina run along the labial face above the laminae; the occlusal face shows foramina near the juncture of the laminae, and the lingual face generally bears foramina between the laminae just below the crown.
Using the published record to identify this toothplate design is highly problematic. Hovestadt-Euler and Hovestadt (pers com. 2007) note that in the extant genus, the lateral file-count is variable and the diagnostic characteristic of the genus is the elongated medial tooth and the presence of one or more lateral files. At Lee Creek, otherwise similar toothplates have been found with one (fig. ), two (fig. ) and three (fig. a; left, termino-lateral positions missing) lateral files -- tending to validate their observations with the Recent taxon.
Commenting on Lee Creek fossil toothplates, Hovestadt-Euler and Hovestadt (pers. com. 2007) note, "It is also difficult to say that these are really new species and not for example P. apenninus COSTA 1850, which is also from the Miocene or P. gemmellaroi SALINAS 1901 or P. siculus SALINAS 1901". There certainly are multiple instances of this dentition-design being described; an early US example would be Myliobatis gigas COPE 1867 (two lateral files) from the Miocene of Charles Co., MD (see Eastman, 1904 Plate XXIX 1a & b). Cappetta's (1987) A. meridionalis illustration (3 lateral files) likely played a part in Iturralde-Vinent et al (1998) describing Aetomylaeus cojimarensis (1 lateral file) and A. cubensis (2 lateral files) from the Miocene of Cuba. Purdy et al (2001: 93) took the prudent approach attributing this dentition-design to Pteromylaeus sp.
Recent seas include two species, Pteromylaeus asperrimus (GILBERT, 1898) from the eastern Pacific and P. bovinus (GEOFFROY SAINT-HILAIRE, 1817) of the eastern Atlantic. During the Miocene, the western Atlantic, Gulf coast and eastern Pacific likely included a single species which was probably at that time the same as present in the eastern Atlantic. The multiple described Miocene taxa would best be synonymized with P apenninus or whichever proves to be the earliest described Miocene species. Arguably, the western Atlantic/Caribbean population could represent a distinct species; in that case, P. gigas would have priority. As a point of interest, note the similarity of the dentition-designs of Pteromylaeus and Pseudaetobatus from the Eocene of Virginia.