Pseudaetobatus undulatus, Cicimurri & Ebersole, 2015

Cicimurri, DJ & Ebersole, JA, 2015, Two new species of Pseudaetobatus Cappetta, 1986 (Batoidei: Myliobatidae) from the southeastern United States, Palaeontologia Electronica (London, England) 24 (1), pp. 1-17 : 9-11

Pseudaetobatus undulatus sp. nov.

Figure 6

zoobank.org/ F5F4BAC2-B808-42F0-AF11-4FD8B8BCD907

Etymology. Species so named for the undulating nature of the lateral teeth.

Hypodigm. SC 2013.38.91 (holotype), upper right distal-most lateral tooth ( Figure 6.1 ); SC 2013.38.84 (paratype), lower median tooth ( Figure 6.6 ); SC 2013.38.86 (paratype), upper median tooth ( Figure 6.8 ); SC 2001.1.5.1 (paratype), lower right distal-most lateral tooth ( Figure 6.5 ); SC 2001.1.5.2 (paratype), intermediate lateral tooth ( Figure 6.4 ).

Type locality. 33.504444 N, - 84.742778 W (N 33° 30' 16" lat., W 81° 44' 34" long.), Aiken , Aiken County, South Carolina .

Type horizon. Dry Branch Formation, approximately 2.0 m below contact with overlying Tobacco Road Formation.

Additional material. Abandoned clay pit north of the Aiken city limit, 33.624867 N, - 81.681713 W; Aiken County, SC; Dry Branch Formation - SC 96.97.52, 22 median tooth fragments; SC 96.97.53, lateral tooth. Type locality SC 2001.1.3, 110 partial median teeth; SC 2001.1.4.1, upper left distal-most lateral tooth ( Figure 6.2 ); SC 2001.1.4.2, lower right distal-most lateral tooth; SC 2001.1.4.3, lateral tooth; SC 2001.1.5.3, 8 lateral teeth; SC 2001.1.6, lateral tooth; SC 2001.1.7, lower left distal-most lateral tooth; SC 2013.38.85, upper median tooth ( Figure 6.10 ); SC 2013.38.87, upper median tooth; SC 2013.38.88, incomplete upper median tooth; SC 2013.38.89, incomplete upper median tooth; SC 2013.38.90, lower median tooth ( Figure 6.7 ); SC 2013.38.92, lower right distal-most lateral tooth; SC 2013.38.93.1, upper right distal-most lateral tooth; SC 2013.38.93.2, upper left distal-most lateral tooth; SC 2013.38.93.3, lower left distal-most lateral tooth ( Figure 6.3 ); SC 2013.38.93.4, two upper distal-most lateral teeth; SC 2013.38.94, 12 lower distal-most lateral teeth; SC 2013.38.95, intermediate lateral tooth; SC 2013.38.96.1, intermediate lateral tooth; SC 2013.38.96.2, intermediate lateral tooth; SC 2013.38.96.3, three intermediate lateral teeth; SC 2013.38.97, 88 partial median teeth.

Diagnosis. Upper and lower tooth morphologies as in Pseudaetobatus casieri and P. belli sp. nov., but smaller in overall size than the latter species. The distal-most lateral teeth are the most diagnostic, and these are distinguished from equivalent teeth of all other Pseudaetobatus species by their sinuous outline in labial/lingual view.

Description. Upper and lower median teeth have a six-sided and very wide but short (labio-lingually) crown. Upper median teeth are rectilinear, with the largest complete tooth (SC 2013.38.85) measuring slightly over 2.2 cm in width and 0.35 cm in length ( Figure 6.10 ). Lower median teeth are arcuate (distal ends of teeth curve lingually), and the largest complete specimen (SC 2013.38.84) measures 1.8 cm in width (slight damage to left corner) and 0.4 cm in length ( Figure 6.6 ). Some fragments indicate that teeth can attain a slightly larger size. The crowns of median teeth have a rectangular cross section. The labial face may be vertical or slightly inclined lingually, and it is ornamented with fine vertical wrinkles. The lingual face is nearly always vertical and bears fine vertical wrinkling and/or conspicuous rugosities. Mesial and distal margins of the crown are angular ( Figure 6.7 -8). A thick, rounded lingual transverse ridge at the crown foot extends along the entire width of the tooth. The ridge profile is enhanced by parallel furrows immediately above and below, and the superjacent furrow is deeply impressed. A shallow groove extending along the entire labial face represents the juncture between the crown and the root. The root is polyaulocorhizous and extends distally past the crown, with the very oblique labial face bearing numerous short transverse furrows that nearly intersect with lamellae located on the flat basal attachment surface.

We associate three lateral tooth morphotypes with the median teeth described above based on crown ornamentation, nature of the lingual longitudinal ridge, and root morphology. The three morphologies are equivalent to those described for Pseudaetobatus belli sp. nov., including upper and lower distal-most laterals, and intermediate lateral. The intermediate lateral teeth have a six-sided crown that is slightly asymmetrical, and straight margins meet at sharp angles ( Figure 6.4 ). The upper and lower distal-most lateral tooth types are similar to those of P. casieri and P. belli sp. nov., with presumed uppers ( Figure 6.1-2 ) being wider than the lowers ( Figure 6.3, 6.5 ), and the mesial margin being angular but the distal margin being drawn out into a pointed, lingually directed projection. The crowns of P. undulatus sp. nov. are sinuous in labial/lingual view due to median concavity and basal curling of the distal margin ( Figures 6.1.3 , 2.1-2 , 3.1-2 ).

Remarks. The median teeth of Pseudaetobatus undulatus sp. nov. differ from those of P. belli sp. nov. in that they are smaller in overall size (SC 2013.38.84 is only half as large as the P. belli holotype), the lingual crown face is more vertical, and the groove above the lingual longitudinal ridge is more deeply impressed. The distal-most lateral teeth of P. undulatus sp. nov., uppers and lowers, are easily distinguished from P. casieri and P. belli sp. nov. in having undulating crowns (those of the latter two species are rather flat). In addition, the distal-most lateral teeth of P. casieri are wider and have more elongated disto-lingual projections than either P. belli sp. nov. or P. undulatus sp. nov. ( Cappetta, 1986).

Stratigraphic and geographic range. The species is thus far only known from the upper Eocene (Priabonian) Dry Branch Formation of Aiken County, South Carolina .

Figures

FIGURE 2. Chronostratigraphy, lithostratigraphy, and biostratigraphy of lower-to-middle Eocene strata of eastern Mississippi and Alabama. Modified from Bybell and Gibson (1985).

FIGURE 3. Chronostratigraphy, lithostratigraphy, and biostratigraphy of middle-to-upper Eocene strata of south-central South Carolina. Abbreviation: O’burg = Orangeburg.

FIGURE 6. Pseudaetobatus undulatus sp. nov. hypodigm and other specimens from the upper Eocene Dry Branch Formation, Aiken County, South Carolina. 1, SC 2013.38.91, upper right distal-most lateral tooth (holotype), basal (1.1), distal (1.2), labial (1.3), mesial (1.4), lingual oblique (1.5), and occlusal (1.6) views. 2, SC 2001.1.4.1, upper left distal-most lateral tooth, labial (2.1), lingual (2.2), and occlusal (2.3) views. 3, SC 2013.38.93.3, lower left distal-most lateral tooth, labial (3.1), lingual (3.2), and occlusal (3.3) views. 4, SC 2001.1.5.2, intermediate lateral tooth (paratype), basal (4.1), distal (4.2), labial (4.3), mesial (4.4), lingual oblique (4.5), and occlusal (4.6) views. 5, SC 2001.1.5.1 (paratype), lower right distal-most lateral tooth, mesial (5.1), lingual oblique (5.2), distal (5.3), labial (5.4), and occlusal (5.5) views. 6, SC 2013.38.84, lower median tooth (paratype), lingual oblique (6.1), basal (6.2), and occlusal (6.3) views. 7, SC 2013.38.90, lower median tooth, lingual oblique view. 8, SC 2013.38.86, upper median tooth (paratype), lingual oblique (8.1), baso-lingual (8.2), and occlusal (8.3) views. 9, Occlusal view of hypothetical reconstruction of part of the upper dentition. This consists of specimens shown in 1 (SC 2001.1.5.2), and 8 (SC 2013.38.86. 1 and 4 were reduced in size to be consistent with 8, and they were reversed to also represent the right tooth rows. The resulting composite series was then replicated. 10, SC 2013.38.85, upper median tooth, occlusal view. Scale bars equal 0.5 cm.