Orectolobus ziegenhinei Cappetta & Case, 2016

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 : 17-20

Orectolobus ziegenhinei Cappetta & Case, 2016

Fig. 6

Orectolobus ziegenhinei Cappetta & Case, 2016: 46–48 , pl. 1, figs 1–9.

Squatiscyllium aff. nigeriensis Clayton et al., 2013: 16, fig. 2f–g.

Orectolobus sp. – Cappetta 2012: 161, fig. 147.

cf. Eometlaouia sp. – Clayton et al. 2013: 16, figs 2d–e.

Material examined

UNITED STATES OF AMERICA – Alabama • 180 isolated teeth; Claiborne Group ; ALMNH PV1992.28.37 (1 specimen), ALMNH PV1992.28.4 (4 specimens), MMNS VP-8216 (3 specimens), MSC 37008.1 – 2 , MSC 37009, MSC 37010, MSC 37056.1 – 2 , MSC 37068.1 – 2 , MSC 37069.1 – 2 , MSC 37070, MSC 37071, MSC 37164, MSC 37181, MSC 37240.1 – 3 , MSC 37250, MSC 37274, MSC 37303 , MSC 37319.1–43, MSC 37673.1–9, MSC 37692.1–2, MSC 38612.1–2, NJSM 24016, SC 2012.47.34– 35, SC 2012.47.36 (13 specimens), SC 2012.47.37, SC 2012.47.38, SC 2012.47.39 (11 specimens), SC 2012.47.159 (29 specimens), SC 2012.47.244 (3 specimens), SC 2012.47.245 (2 specimens), SC 2012.47.246 (3 specimens), WSU 19, WSU 4, WSU 5036 (28 specimens).

Description

Anterior teeth with tall, triangular cusp that is lingually directed and may be very slightly distally inclined. Main cusp flanked by short lateral shoulders that may be oblique or perpendicular to the cusp. A smooth cutting edge extends across the entire crown, dividing it into convex labial and lingual parts. The labial crown foot bears a basally directed protuberance of varying length and width. Lingual crown foot bears a lingually directed protuberance that extends onto the dorsal surface of the root. Root very low with short lobes; heart-shaped in basal view; basal attachment surface is very concave. Root hemiaulocorhizous, with an anterior depression directed towards a large basal foramen. Basal depression located closer to the posterior margin. Posteriorly, the basal foramen is connected to a foramen on the lingual face of the root by a narrow canal; sometimes these foramina are joined by a groove. The dorsal surface of the lingual side of the root bears two or three small foramina, located below the crown foot, on each side of the crown protuberance. Crowns of lateral and posterior teeth are like those in anterior positions except that they are wider (due to more elongated shoulders) and the cusp is lower and more obviously distally inclined. Root is wider, with more elongated lobes, and the number of dorsal foramina on the root varies from three to six. Some lateral teeth have one to two pairs of lateral cusplets. Short longitudinal ridges present on the labial face of lateral shoulders of small teeth (<5 mm), but only a short medial ridge may occur on large teeth.

Remarks

The Orectolobus ziegenhinei teeth in our sample were directly compared to those within two Recent Orectolobus japonicus Regan, 1906 jaws, one a presumed adult set measuring 16.5 cm wide and the other a presumed juvenile or subadult set measuring 11 cm wide. Our observations of these two O. japonicus jaws indicate that a degree of ontogenetic heterodonty occurs, with older/larger specimens lacking or having a single pair of cusplets on their lateral teeth, whereas lateral teeth of younger/smaller specimens have one-to-two pairs of cusplets. Furthermore, the lower dentition of O. japonicus has a single symphyseal tooth that is nearly identical to those in the anterior positions but has mesial and distal shoulders that are equal in length. On the anterior teeth, the distal lobe is slightly elongated and lateral cusplets are absent. Lateral teeth are broader than anterior teeth, and all have lateral cusplets. The first lateral tooth is distinct, as it has a distal cusplet, but no mesial cusplet(s). The right and left sides of the upper and lower dentitions have a single row of anterior teeth, and the upper dentition has a row of minute symphyseal teeth. Upper lateral teeth are more lingually inclined than lower laterals. In profile view, the upper anterior teeth are slightly more sigmoidal than those in the lower jaw. Ornamentation, occurring as striations at the crown foot, is present on the labial crown face of the anterior and lateral teeth in both jaw sets, but is coarser and more conspicuous on the juvenile/subadult specimen.

Comparison of the fossil material to Recent Orectolobus japonicus teeth revealed that the ornamentation on the Lisbon Formation specimens generally extends higher on the crown, lateral teeth are not as distally inclined, and the teeth have a shorter crown. These differences aside, the fossil teeth in our sample compare very favorably with those within the extant jaws, allowing us to draw several conclusions regarding the fossil species. Our sample of fossil teeth exhibit a similar degree of monognathic and dignathic heterodonty, as lower symphyseal (symmetrical teeth), anterior (teeth with elongated distal heels), first lateral (teeth with mesial cusplet present, but no distal cusplet), and lateral teeth (teeth with one to two pairs of lateral cusplets) have been identified in our sample. However, the crown on the fossil lateral teeth is less distally inclined than those in the Recent jaw sets we examined; dignathic heterodonty is therefore less apparent because it is difficult to distinguish upper from lower files. We also note a pattern within the fossil teeth in our sample that we interpret as ontogenetic heterodonty based on our observation of the O. japonicus jaws, as specimens with single and double pairs of lateral cusplets are present, indicating the presence of both juvenile and adult teeth in our sample.

Our analysis of both the fossil and Recent teeth allows us to emend the species identifications previously made by Clayton et al. (2013). These authors identified two species, cf. Eometlaouia and Squatiscyllium aff. nigeriensis, based on the presence (cf. Eometlaouia ) or absence ( Squatiscyllium ) of lateral cusplets. The figured cf. Eometlaouia specimen ( Clayton et al. 2013: fig. 2: d–e) has an elongated distal heel and distal cusplet, but no mesial cusplet, suggesting it instead belongs to a first lateral tooth of O. ziegenhinei . The Squatiscyllium aff. nigeriensis tooth ( Clayton et al. 2013: fig. 2: f–g) has mesial and distal shoulders of equal length, indicating it is an O. ziegenhinei lower symphyseal tooth. Cappetta (2012: fig. 147) figured three “ Orectolobus sp.” teeth purportedly from the Tallahatta Formation in Mississippi, which Cappetta & Case (2016) later referred to O. ziegenhinei while at the same time correcting the error in stratigraphic horizon and geographic location, as the teeth were actually derived from the contact zone of the Tallahatta and Lisbon formations at site ACov- 11 in Covington County, AL. According to Cappetta & Case (2016), the O. ziegenhinei teeth from site ACov-11 represent the stratigraphically oldest member of this genus.

Stratigraphic and geographic range in Alabama

To date this taxon appears stratigraphically confined to the contact of the Tallahatta and Lisbon formations at sites ACh-14 and ACov-11, and the basal Lisbon Formation at site ACov-11. Middle Lutetian, zones NP14 and NP15.

Superfamily Hemiscyllioidea Naylor et al., 2012

Family Ginglymostomatidae Gill, 1862

Figures

Fig. 6. Orectolobus ziegenhinei Cappetta & Case, 2016, teeth. A–E. MSC 37009, Tallahatta/Lisbon formation contact zone, courtesy of Carl Sloan. A. Oral view. B. Lingual view. C. Distal view. D. Labial view. E. Basal view. F–J. MSC 37181, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. F. Oral view. G. Lingual view. H. Distal view. I. Labial view. J. Basal view. K–O. MSC 37056.1, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. K. Oral view. L. Lingual view. M. Distal view. N. Labial view. O. Basal view. P–T. MSC 37319.1, basal Lisbon Formation. P. Oral view. Q. Lingual view. R. Mesial view. S. Labial view. T. Basal view. U–Y. MSC 37319.3, basal Lisbon Formation. U. Oral view. V. Lingual view. W. Mesial view. X. Labial view. Y. Basal view. Labial at top in oral and basal views. Scale bars = 2 mm.