Physogaleus alabamensis ( Leriche, 1942 ) Ebersole & Cicimurri & Stringer, 2019

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 : 92-95

Physogaleus alabamensis ( Leriche, 1942) comb. nov.

Fig. 33

Galeocerdo alabamensis Leriche, 1942: 48 , pl. 4, fig. 2.

Galeocerdo alabamensis – Thurmond & Jones 1981: 63 , fig. 28, right.

Galeocerdo latidens – Van den Eeckhaut & De Schutter 2009 : pl. 20, figs 9–11. — Clayton et al. 2013: 68, fig. 3j. — Cappetta & Case 2016: 57, pl. 8, 12–16.

Galeocerdo eaglesomei – Van den Eeckhaut & De Schutter 2009 : pl. 20, fig. 8.

Physogaleus sp. – Cappetta & Case 2016: 58, pl. 7, figs 12–13.

Galeorhinus sp. – Pandey et al. 2018: fig. 4a–b.

Material examined

UNITED STATES OF AMERICA – Alabama • 507 isolated teeth; Claiborne Group ; ALMNH PV1989.4.125a (2 specimens), ALMNH PV 1989.4.21 (2 specimens), ALMNH PV1989.4.219b (6 specimens), ALMNH PV1992.28.17 (2 specimens), ALMNH PV1992.28.35 (6 specimens), ALMNH PV2000.1.43.3, ALMNH PV2005.6.441, ALMNH PV 2016.4.25, MMNS VP-8197 (19 specimens), MMNS VP-8198 (3 specimens), MMNS VP-8199 (122 specimens), MMNS VP-8217 (7 specimens), MMNS VP-8948 (2 specimens), MMNS VP-8949, MSC 2180.1 , MSC 2180.3 , MSC 2381.2 , MSC 2382.1 – 3 , MSC 34405.1 – 4 , MSC 34405.6 MSC 34408.8 , MSC 34408.10 – 12 , MSC 37020, MSC 37104, MSC 37105.1 – 4 , MSC 37107, MSC 37137.1 – 3 , MSC 37144, MSC 37145, MSC 37154.1 – 3 , MSC 37300, MSC 37344, MSC 37628, MSC 37635.2 , MSC 37637.1 – 2 , MSC 37653.1 – 2 , MSC 37655.1 – 2 , MSC 37663.1 – 2 , MSC 37676, MSC 38152, MSC 38153.1 – 5 , MSC 38154.1 – 10 , MSC 38155.1 – 2 , MSC 38156.1 – 12 , MSC 38169, MSC 38170.1 – 4 , MSC 38190.1 – 2 , MSC 38191, MSC 38192.1 – 32 , MSC 38193.1 – 4 , MSC 38195.1 – 2 , MSC 38215, MSC 38216.1 – 2 , MSC 38242.1 – 3 , MSC 38243.1 – 3 , MSC 38244.1 – 11 , MSC 38245.1 – 9 , MSC 38285.1 – 3 , MSC 38288, MSC 38318.1 – 4 , MSC 38319.1 – 4 , MSC 38320, MSC 38321.1 – 3 , MSC 38427.1 – 13 , MSC 38511.1 – 2 , SC 2012.47.166 (9 specimens), SC 2012.47.174 (9 specimens), SC 2012.47.184 (12 specimens), SC 2012.47.206 (85 specimens), SC 2012.47.252 (9 specimens), WSU 1 , WSU 2 , WSU 5001 , WSU 5039 (17 specimens), WSU CC 527 (2 specimens), WSU CC 533 (2 specimens), WSU CC 832.1 (2 specimens) .

Description

Anterior teeth with nearly triangular crown; mesial and distal cutting edges slightly convex. Lingual crown face convex; labial face flat to very weakly convex; crown enameloid smooth. Mesial cutting edge denticulated along lower two-thirds, upper two-thirds smooth. Distal cutting edge similar, contiguous or with slightly differentiated distal heel. Denticulation on distal edge decreases in size basally. Upper part of mesial and distal cutting edges form triangular, nearly erect cusp. Root bulky, bilobate, with low, elongated, highly divergent lobes; pronounced lingual boss bisected by nutritive groove, which contains large nutritive foramen. Lateral teeth wide, with more convex mesial cutting edge, short distal cutting edge, distally directed cusp; conspicuous distal heel separated from cutting edge by pronounced notch; heel with up to 12 serrations, decreasing in size basally. Root wider, more labiolingually compressed than anterior teeth. Root lobes generally rounded, widely diverging; interlobe area weakly concave to absent. Basal root face distinctly flattened. Conspicuous nutritive groove on lingual root boss; multiple foramina located on labial root face. Gynandric heterodonty expressed as male lower anterior teeth with taller, mesiodistally thinner, more sigmoidal crown than female teeth.

Remarks

Numerous teeth in our sample appear to be conspecific with Galeocerdo alabamensis , a taxon erected by Leriche (1942) based on a single tooth derived from Jackson Group deposits at Cocoa in Choctaw County,AL.Although Leriche (1942: 11) did not provide more specific details regarding the stratigraphic horizon of this tooth, he noted that the collection of teeth he examined was collected “by C. Schuchert in Alabama and Mississippi, partly in the Zeuglodon beds.” In Alabama, deposits within the town of Cocoa were designated the type section for the Cocoa Sand Member of the Yazoo Clay of the Jackson Group, the upper portion of which grades into a Zeuglodon -bearing bed ( Cooke 1933). Thus, it can be said with some certainty that the G. alabamensis holotype was collected from the upper portion of the Priabonian Cocoa Sand Member.

Upon reexamination of the holotype of G. alabamensis , USNM 8256, we determined that the species name is valid and that it is more appropriately assignable to Physogaleus , not Galeocerdo . USNM 8256 exhibits several characteristics that better ally it with Physogaleus , including a mesiodistally thinner crown that is sinuous in profile view and smooth cutting edges (although cusplets are developed on the base of the mesial edge and on the distal heel). In contrast, mesial cutting edges of all the species of Galeocerdo examined, both fossil and extant (for a discussion on the differences between Physogaleus and Galeocerdo , see Galeocerdo clarkensis and G. eaglesomei below), have a thick, flat crown, completely (or nearly completely) serrated mesial cutting edge, and serrated distal cutting edge. Furthermore, in a comparison with the teeth in our Claiborne sample, we conclude that USNM 8256 represents an upper lateral tooth, and that the dentition of this species is very similar to that of another Claiborne species, Physogaleus secundus . Our sample includes numerous teeth of both species, from all jaw positions, including upper and lower anterior, lateral, and symphyseal positions, as well as male teeth. These two taxa are differentiated from each other by the number of mesial denticulations and distal cusplets present, with teeth of Physogaleus alabamensis comb. nov. having well-defined cusplets on the mesial cutting edge that extend up to two-thirds the height of the crown, and up to 12 denticulations on the distal heel. In contrast, P. secundus has indistinct, if any, denticulation that is limited to the lower part of the mesial cutting edge, and four or less cusplets on the distal heel. Although these differences could be attributed to ontogeny within a single species, our sample of both morphologies contains teeth ranging in mesiodistal width from 4 mm to 17 mm. This indicates that the number of denticulations does not increase with the age of the animal (ontogeny), but rather that this is a taxonomically useful characteristic that can be used to differentiate these two species.

Several other Eocene species of Physogaleus have been described in the literature, including P. americanus (Case, 1994) , P. cuvieri (Agassiz, 1835) , P. latecuspidatus Müller, 1999 , P. rosehillensis Case & Borodin, 2000 , and P. secundus ( Winkler, 1876) . A comparison to these varied taxa indicates that the P. alabamensis comb. nov. morphology is both unique and valid. The differences between P. alabamensis comb. nov. and P. secundus have been noted above, and P. rosehillensis differs by having fewer denticulations than P. alabamensis comb. nov. Also, Cappetta & Case (2016) have suggested that the rosehillensis morphology should be considered a junior synonym of P. secundus because it falls within the morphological range of this latter taxon. Although the teeth of P. latecuspidatus Müller, 1999 have more defined mesial denticles than generally observed on P. secundus , it still has fewer mesial denticles and distal cusplets than on P. alabamensis comb. nov. Physogaleus latecuspidatus may also fall within the morphological range, and could be considered a junior synonym of P. secundus . The teeth of P. cuvieri (Agassiz, 1835) have three-to-five distal cusplets and very few, if any, mesial denticles. Not only do the number of mesial denticles and distal cusplets separate these teeth from those of P. alabamensis comb. nov., but Fanti et al. (2016) provided a convincing argument that P. cuveri instead belongs in Galeorhinus . The teeth of P. alabamensis comb. nov. differ from those of P. americanus by having more mesial denticles and distal cusplets, and by lacking the single large mesial cusplet as seen on the P. americanus type specimens (see Case 1994a: figs 214–218).

The P. alabamensis comb. nov. teeth in our sample most closely resemble those of the Oligocene and Miocene Physogaleus latus ( Storms, 1894) as both have distinct mesial and distal cusplets. The teeth of P. alabamensis comb. nov., however, can be differentiated from this latter taxon by the number of distal cusplets which Storms (1894) reported never exceeds five on P. latus , although as many as 12 can be present on P. alabamensis comb. nov. The similarity in morphology between these two species, and the slightly younger stratigraphic age of P. latus , suggests that these two taxa might be closely aligned.

Thurmond & Jones (1981) recognized the validity of the alabamensis morphology, noting the sinuosity of its crown. Our reexamination of their two figured specimens revealed that one specimen belongs to P. alabamensis comb. nov. (fig. 28, right), but the other (fig. 28, left) is Galeocerdo eaglesomei . Manning & Standhardt (1986) suggested that Galeocerdo clarkensis was a junior synonym of Galeocerdo alabamensis and that the former represented the upper teeth of the latter. However, serrations on the teeth of G. clarkensis are compound and extend nearly to the cusp apex on the mesial and distal edges (see below), whereas cusplets are not serrated on P. alabamensis comb. nov. and cutting edges on the main cusp are smooth. This indicates that the morphologies belong to entirely different taxa. Parmley & Cicimurri (2003) later identified teeth within their sample from the Clinchfield Formation in Georgia as belonging to Galeocerdo alabamensis , noting that the teeth were completely serrated and that serrations were compound. Their determination was based on White’s (1956) identification of teeth from South Carolina as G. alabamensis , but upon our reexamination, it is clear that Leriche’s (1942) alabamensis holotype is significantly different from the Clinchfield material. Our reexamination of Galeocerdo teeth from the Clinchfield Formation suggests that they compare more favorably to Galeocerdo clarkensis .

Several teeth in our sample appear conspecific to those illustrated by Van den Eeckhaut and De Schutter (2009: pl. 20, figs 9–11) as Galeocerdo latidens . Not only are these teeth similar in overall form to Physogaleus alabamensis comb. nov., they also have the same number of cusplets on the mesial and distal cutting edges, and lack serrations above the distal notch and on the upper third of the mesial blade. Van den Eeckhaut & De Schutter (2009: pl. 20, fig. 8) also illustrated a tooth that they assigned to G. eaglesomei , but this specimen lacks denticulations on the upper portion of the crown, and it exhibits a pronounced distal notch, a characteristic not well defined on the teeth of G. eaglesomei . We believe that the two teeth are more appropriately assigned to Physogaleus , and that they are comparable to P. alabamensis comb. nov. as described above.

Both Clayton et al. (2013: fig. 3j) and Cappetta & Case (2016: pl. 8, figs 12–16) illustrated teeth that they identified as Galeocerdo latidens that we herein refer to P. alabamensis comb. nov. These teeth all have more than four cusplets on the distal heel, they have well-defined mesial denticles that do not extend to the cusp apex, and serrations are lacking on the cutting edges. Cappetta & Case (2016: 58, pl. 7, figs 12–13) also described teeth that they assigned to Physogaleus sp., noting the morphology was common in the Ypresian of Prémontré in the Paris Basin. It is our opinion that these teeth are also conspecific with P. alabamensis comb. nov.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the Meridian Sand Member of the Tallahatta Formation and the lower Tallahatta Formation at site ADl-1, the Tallahatta Formation at site AMo-8, the contact of the Tallahatta and Lisbon formations and the basal Lisbon Formation at site ACov-11, the “upper” Lisbon Formation at site ACl-3, the basal Gosport Sand at site ACl-4, and the Gosport Sand at sites ACh-21 and ACl-15. Upper Ypresian to middle Bartonian, zones NP12 to NP17.

Figures

Fig. 33. Physogaleus alabamensis (Leriche, 1942) comb. nov., teeth. A–C. MSC 2382.1, lateral tooth, Gosport Sand. A. Labial view. B. Mesial view. C. Lingual view. D–F. MSC 2382.3, lateral tooth, Gosport Sand. D. Labial view. E. Mesial view. F. Lingual view. G–I. MSC 34408.2, lateral tooth, lower Tallahatta Formation. G. Labial view. H. Mesial view. I. Lingual view. J–L. MSC 38154.1, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. J. Labial view. K. Mesial view. L. Lingual view. M–O. MSC 38156.1, anterolateral tooth, lower Tallahatta Formation. M. Labial view. N. Mesial view. O. Lingual view. P–R. MSC 38154.3, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. P. Labial view. Q. Mesial view. R. Lingual view. S–U. MSC 37154.3, anterolateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. S. Labial view. T. Mesial view. U. Lingual view. V–X. MSC 38485.9, lateral tooth, basal Lisbon Formation. V. Labial view. W. Mesial view. X. Lingual view. Y–AA. MSC 38242.2, lateral tooth, basal Gosport Sand. Y. Labial view. Z. Mesial view. AA. Lingual view. BB–DD. MSC 38485.2, lateral tooth, basal Lisbon Formation. BB. Labial view. CC. Mesial view. DD. Lingual view. EE– GG. MSC 38511.1, lateral tooth, basal Gosport Sand. EE. Labial view. FF. Mesial view. GG. Lingual view. HH–JJ. MSC 37144, male anterior tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. HH. Labial view. II. Mesial view. JJ. Lingual view. KK–MM. MSC 38156.6, male anterior tooth, lower Tallahatta Formation. KK. Labial view. LL. Mesial view. MM. Lingual view. Scale bars = 5 mm.