Dasyatis Rafinesque, 1810

Ebersole, Jun A., Cicimurri, David J. & Stringer, Gary L., 2019, Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths, European Journal of Taxonomy 585, pp. 1-274 : 112-116

Genus Dasyatis Rafinesque, 1810

Type species

Dasyatis ujo Rafinesque, 1810 , Recent.

“ Dasyatis ” aff. D. charlisae Case, 1981 Fig. 40 A–L

Dasyatis charlisae Case, 1981: 69 , text-fig. 8, pl. 7, figs 1a–e, 2a–e, 4a–d.

Dasyatis sp. 1 – Clayton et al. 2013: fig. 5c–d.

Material examined

UNITED STATES OF AMERICA – Alabama • 8 isolated teeth; Claiborne Group; SC 2012.47.240, SC 2012.47.242, SC 2012.47.243, WSU 29, WSU CC 441, WSU CC 448, WSU CC 449, WSU CC 450.

Description

Only low-crowned teeth present. Transverse crest divides crown into labial and lingual halves. Crown is triangular in mesial and distal views; root lingually projected. Crown overhangs the root on all sides; base of labial face well developed, forming a labial shelf. Lingual crown face ranges from flat to slightly concave; labial face concave to convex, depending on tooth position. In occlusal view, labial face ranges from diamond to oval in outline; lingual face triangular and basally elongate. Basal margin of lingual crown face strongly convex. Punctate ornamentation present on entire labial crown face, at times extending just past the transverse ridge onto the periphery of lingual face. Root bilobed; separated from the crown by a shallow groove. Multiple foramina present within the median root furrow.

Remarks

Clayton et al. (2013) recognized two Dasyatis tooth morphologies within their sample from site ACov- 11 in Covington County, AL. Assigned to “ Dasyatis sp. 1” and “ Dasyatis sp. 2”, these morphologies were differentiated by their overall shape and development of ornamentation on their labial crown face.

To test whether the degree of crown ornamentation is a taxonomically useful characteristic for differentiating these otherwise similar taxa, our sample of “ Dasyatis ” teeth were directly compared to a modern set of dasyatid jaws (genus and species indet.) from the MSC collection. Our observations of this dentition are as follows:

1. Upper anterior teeth have a labial face that is obliquely flat to weakly convex.

2. Upper lateral teeth have a lower crown than anteriors but have a transverse crest that forms a sharper edge.

3. The labial face of the teeth is concave, and the apical one-third to one-half of the labial face is ornamented with vertical wrinkling.

4. The lower portion of the teeth have a reticulated ornamentation.

5. The ornamentation extends to lingual side of transverse crest.

6. Teeth in the lower jaw are similar to those in the upper jaw, but the lower jaw appears to have more lateral rows containing teeth with a concave labial face.

These observations indicate that many of the morphological characteristics cited for the isolated teeth of Dasyatis are ambiguous and can be attributed to heterodonty (monognathic, dignathic, and gynandric). However, crown ornamentation appears to be consistent across all tooth files, upper and lower, within a dentition, suggesting the extent and type of ornamentation can be useful in differentiating the various taxa. This lends support to the presence of two species being present within our Claiborne sample.

Cappetta & Case (2016) recognized two Dasyatis species from site ACov-11, including Dasyatis charlisae Case, 1981 and Dasyatis jaekeli ( Leriche, 1905) . Of these, Cappetta & Case (2016) also referred Dasyatis sp. 1 of Clayton et al. (2013) to D. charlisae . Although several of our Lisbon Formation teeth are similar to D. charlisae in that the ornamentation covers the entire labial face, the species is difficult to evaluate because Case (1981) based the species on only five teeth, all of which are slightly different in size, shape, and ornament. We tentatively follow Cappetta & Case (2016) regarding taxonomic assignment of this tooth type. These teeth of D. jaekeli are differentiated from D. charlisae by having a labial face bearing fine pitting that does not extend to the lingual side of the transverse crest. Placing the two Lisbon Formation morphologies within Dasyatis is potentially problematic. Extant Dasyatidae consists of eight genera and at least 88 species ( Nelson et al. 2016), and a recent phylogenetic analysis organized the species into the subfamilies Dasyatinae , Neotrygoninae, Urogymninae, and Hypolophinae ( Last et al. 2016). The results presented by Last et al. (2016) showed the genera Dasyatis and Himantura to be paraphyletic, and the authors resorted to using external morphology to ascribe several species to these genera. Because these recent taxonomic revisions were based on genetics and body shape, as opposed to tooth morphology, it is currently unclear how identification of extinct members of the Dasyatidae will be impacted. The difficulty in identifying fossil Dasyatidae teeth was discussed by Ward (1979), who explained that the morphological characteristics used to define extant and fossil Dasyatis teeth are shared among several different genera within the family. Due to the lack of taxonomic clarity among the fossil members of this family, we suggest the conservative usage of “ Dasyatis ” for these teeth because they could belong to any number of different genera within the Dasyatidae .

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the basal Lisbon Formation at site ACov-11 and the “upper” Lisbon Formation at site ACh-8. Lower Lutetian to middle Bartonian, zones NP15 to NP17.

“ Dasyatis ” jaekeli ( Leriche, 1905) Fig. 40 M–X

Trygon jaekeli Leriche, 1905: 100 , pl. 4, figs 29–32.

Dasyatis jaekeli – Casier 1946: 101 , pl. 3, fig. 2a–h.

Dasyatis sp. 2 – Clayton et al. 2013: fig. 5e–f.

Material examined

UNITED STATES OF AMERICA – Alabama • 16 isolated teeth; Claiborne Group ; MSC 35785.1 – 3 , SC 2012.47.8, SC 2012.47.9 (3 specimens), SC 2012.47.10, SC 2012.47.11, SC 2012.47.12 (5 specimens), SC 2012.47.241, WSU 14 .

Description

High-crowned and low-crowned morphologies present. Transverse crest on low-crowned teeth divides crown into labial and lingual halves. Crown triangular in mesial and distal views; root projects lingually. Crown overhangs root on all sides; base of labial face well developed forming a labial shelf. Lingual crown face ranges from flat to slightly concave; labial face concave to convex depending on tooth position. In occlusal view, labial face ranges from diamond-to-oval in outline; lingual face triangular and basally elongate. Basal margin of lingual crown face strongly convex. Punctate ornamentation present on labial crown face; ornamentation restricted to the crown base or along the transverse crest. Root bilobed, separated from crown by a shallow groove. Multiple foramina present within the median furrow of the root. High-crowned (male) teeth like the low-crowned morphology, but with more triangular labial crown face. In mesial or distal views, the lingual crown face is concave and the labial face convex; apex of the crown lingually projected.

Remarks

Clayton et al. (2013) identified this tooth type as Dasyatis sp. 2 and differentiated it from their Dasyatis sp. 1 specimens based on the highly convex labial face bearing fine pitting that does not extend to the lingual side of the transverse crest. The Dasyatis sp. 1 specimens figured by Clayton et al. (2013: pl. 70, figs 5c–d) were later assigned to D. jaekeli by Case & Cappetta (2016), and our comparison of the Lisbon sample to the type suite of D. jaekeli ( Leriche 1905: pl. 4, figs 29–32) indicates they do indeed belong to this taxon.

Both high-crowned and low-crowned tooth morphologies have been identified within our sample, which we consider to be conspecific due to the shared fine pitting on the labial face. It is important to note that several authors (i.e., Case 1981; Cappetta 2012; Cappetta & Case 2016) have erroneously assumed that because the high-crowned dasyatid teeth can be attributed to males, the low-crowned morphology must belong to female individuals. However, depending on the species, both males and females can have lowcrowned teeth, and the males of some species may develop highly cuspidate teeth during the breeding season ( Kajiura & Tricas 1996).

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site ADl-1 and the basal Lisbon Formation at site ACov-11. Upper Ypresian to lower Lutetian, zones NP14 and NP15.

Family incertae sedis

Genus Aturobatis Adnet, 2006

Type species

Aturobatis aquensis Adnet, 2006 , middle Eocene, France.

Figures

Fig. 40. “Dasyatis”, teeth. A–L. “Dasyatis” aff. D. charlisae Case, 1981. A–D. SC2012.47.242, basal LisbonFormation.A.Basiolabialview.B. Oralview.C. Labialview.D. Profileview.E–H. SC2012.47.243, basal Lisbon Formation. E. Basiolabial view. F. Oral view. G. Labial view. H. Profile view. I–L. WSU CC–449, “upper” Lisbon Formation. I. Basiolabial view. J. Oral view. K. Labial view. L. Profile view. — M–X. “Dasyatis” jaekeli (Leriche, 1905). M–P. MSC 35785.1, lower Tallahatta Formation. M. Basiolabial view. N. Oral view. O. Labial view. P. Profile view. Q–T. SC2012.47.9.241, basal Lisbon Formation. Q. Basiolabial view. R. Oral view. S. Labial view. T. Profile view. U–X. SC2012.47.10, male breeding morphology, basal Lisbon Formation. U. Basiolabial view. V. Oral view. W. Lingual view. X. Distal view. Labial at top in oral view. Scale bars = 5 mm.