Eoplinthicus yazooensis Cappetta & Stringer, 2002

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 : 147-149

Eoplinthicus yazooensis Cappetta & Stringer, 2002

Fig. 54

Eoplinthicus yazooensis Cappetta & Stringer, 2002: 51–56 , pl. 1.

Material examined

UNITED STATES OF AMERICA – Alabama • 1 isolated tooth; Claiborne Group ; ALMNH PV1985.35.65 .

Description

A single median tooth is represented in our sample. Tooth is very wide, but labiolingually thin, sixsided. Occlusal surface concave across nearly the entire width; occlusal surface outlined by a sharp, irregular rim. In oral view, crown is conspicuously smaller in area than the crown base. Labial crown face concave, with lower half projecting labially and upper half nearly vertical. Lingual face vertical and straight, slight lingual projection at the crown foot. Very base of lingual crown bears weak transverse ridge immediately above the root. All crown faces with coarse ornamentation of vertical anastomosing and interconnected ridges that become finer apically. Polyaulocorhize root as high as the crown. Labial and lingual faces nearly vertical; 13 narrow lobes are separated by 12 nutritive grooves.

Remarks

When originally described, Eoplinthicus was not directly differentiated from Burnhamia , possibly because the two genera were not known to co-occur within the Yazoo Clay ( Cappetta & Stringer 2002). However, both Eoplinthicus and Burnhamia were collected from the upper Gosport Sand (see above), and a differential diagnosis is provided here. Eoplinthicus yazooensis is now known from three teeth (including two from the Yazoo Clay), all of which can be distinguished from Burnhamia by having an occlusal surface that is significantly smaller in area than the crown base. In contrast, the occlusal surface on Burnhamia teeth is equal to, or only slightly smaller in area than, the crown base. Additionally, the lower half of the labial face of E. yazooensis is broadly rounded, whereas on Burnhamia the labial crown foot is developed into a sharp horizontal or basally directed projection. In profile, the lateral angles of E. yazooensis are not as sharply defined as observed on Burnhamia . Also, the occlusal surface of E. yazooensis bears a series of fine labiolingually oriented striations, as opposed to a somewhat reticulated network of ridges on the oral surface of Burnhamia teeth. The labial margin on E. yazooensis is less sharply defined than Burnhamia , which has a sharp six-sided outline in occlusal view. Cappetta & Stringer (2002) implied that Eoplinthicus was a direct descendant of Burnhamia , but this theory must be further examined in light of the discovery that these taxa were coeval within the Gosport Sand paleoenvironment.

A second Eoplinthicus species, E. underwoodi Adnet et al. 2012 , has been reported from middle-toupper Eocene strata in Africa. This species differs from E. yazooensis in being smaller in size (with six root lamellae) and by having less developed crown ornamentation.

Stratigraphic and geographic range in Alabama

The lone specimen in our sample was collected from the upper Gosport Sand at site ACh-21. Middle Bartonian, Zone NP17.

Batomorphii indet.

Fig. 55

Material examined

UNITED STATES OF AMERICA – Alabama • 3 isolated teeth; Claiborne Group; MSC 37675.1–2, SC 2012.47.154.

Description

Teeth do not exceed 2 mm in crown height. Upper one-half to two-thirds of crown formed into laterally compressed, vertical to slightly lingually curving cusp. Lower one-third to one-half of crown wider, shelf-like laterally and lingually, with labial crown foot developed into small, divergent projections. Labial projections separated by shallow to deep medial embayment. Lingual crown foot straight or with weakly developed medial notch. Crown with trapezoidal to square outline in oral view, but more triangular in profile. Root located at lingual half of crown, bilobate with wide nutritive groove, extends past the lingual crown foot.

Remarks

The crown on these teeth is distinctive for their tall, laterally compressed cusp, conspicuous, diverging basal labial projections and roughly square oral outline. Although similar to teeth of Jacquhermania and the male teeth of “ Dasyatis ” described herein, the three teeth in our sample differ significantly in having a laterally compressed cusp that lacks lateral cutting edges. In addition, male teeth of “ Dasyatis ” bear ornamentation of various types (see above). Although the specimens are morphologically comparable to, and within the size range of, most members of the Torpedinidae , particularly Torpedo , the Lisbon specimens differ from all Recent and fossil Torpedinidae , except Eotorpedo , in lacking distinctive lateral cutting edges extending from the cusp apex to nearly the crown base (Cappetta 1988; Herman et al. 2002).

Eotorpedo White, 1935 can have a cusp similar to the Lisbon specimens described above, as well as labial projections separated by a deep embayment and a notch at the lingual crown foot. A significant difference between the Lisbon specimens and these two species of Eotorpedo is the lack of a basal transverse crest on the Alabama teeth. Some specimens identified as Eotorpedo , including Eotorpedo nolfi Herman, 1974 ( Herman 1974: fig. 1, a-c) and Eotorpedo jaekeli (Case, 1994) (see Case 1994a) may in fact be Jacquhermania ( Cappetta 2012; Cappetta & Case 2016). It is possible that the Claibornian specimens described above represent juvenile teeth of Jacquhermania , but to our knowledge this morphology has not previously been attributed to this genus. Additional, more complete, specimens are needed to more accurately identify this morphology.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the basal Lisbon Formation at site ACov-11. Lower Lutetian, Zone NP15.

Figures

Fig. 54. Eoplinthicus yazooensis Cappetta & Stringer, 2002, median tooth. A–E.ALMNH PV1985.35.65, Gosport Sand. A. Lingual view. B. Labial view. C. Oral view. D. Basal view. E. Profile view. Labial at top in oral and basal views. Scale bar = 1 cm.

Fig. 55. Batomorphii indet., teeth. A–E. MSC 37675.2, basal Lisbon Formation. A. Labial view. B. Lingual view. C. Profile view. D. Oral view. E. Basal view. F–J. MSC 37675.1, basal Lisbon Formation. F. Labial view. G. Lingual view. H. Profile view. I. Oral view. J. Basal view. K–O. SC2012.42.154, basal Lisbon Formation. K. Labial view. L. Lingual view. M. Profile view. N. Oral view. O. Basal view. Labial at top in oral and basal views. Labial at top in oral and basal views. Scale bars = 1 mm.