Galeocerdo clarkensis White, 1956

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 : 103-106

Galeocerdo clarkensis White, 1956

Fig. 36

Galeocerdo clarkensis White, 1956: 127–128 , text figs 24–26, pl. 2, figs 12–14.

Galeocerdo aduncus – Woodward 1889: 446 .

Galeocerdo alabamensis – Parmley & Cicimurri 2003: 170–171 , fig. 6. — Manning 2003: 374, fig. 21.3.3.

Material examined

UNITED STATES OF AMERICA – Alabama • 86 isolated teeth; Claiborne Group ; ALMNH PV1993.2.407 (6 specimens), MSC 188.6 , MSC 188.26 , MSC 188.68 , MSC 188.149 , MSC 188.255 , MSC 188.259 , MSC 188.272 , MSC 188.308 , MSC 2175.21 , MSC 2180.2 , MSC 2378.2 – 3 , MSC 2382.4 , MSC 37402.1 – 3 , MSC 37494.1 – 49 , MSC 37522, MSC 37592, MSC 37604, MSC 37897, MSC 38468, MSC 38469, MSC 38470.1 – 2 , MSC 38509.1 – 2 , MSC 38543.1 – 5 .

Description

Teeth with roughly triangular crown. Mesial cutting edge is uniformly convex, sometimes slightly concave basally. Coarse, weakly compound serrations located at most convex portion of mesial edge; serrations finer basally and apically. Distal cutting edge short, weakly convex, finely serrated nearly to apex, forms distally inclined cusp with mesial edge. Distal heel heavily serrated, separated from distal cutting edge by notch. Heel serrations decrease in size distally; generally, largest serration (just distal to notch) has compound serration pattern on distal side. Labial crown face flat to slightly convex; lingual face convex; enameloid smooth. Root bilobate; lobes short, rounded, divergent; lobes separated by shallow U-shaped interlobe area. Lingual root face high, with weak lingual protuberance bisected by deep nutritive groove.

Remarks

Leriche (1942) erected the species Galeocerdo alabamensis based on a single specimen recovered from upper Eocene deposits at Cocoa in Choctaw County, AL. White (1956) later named G. clarkensis in part based on specimens that Woodward (1889) reported from the Priabonian Yazoo Clay in Clarke County, Alabama. White (1956) justified his new taxon by stating that the teeth of G. clarkensis were evenly serrated on the mesial edge, whereas those on the teeth G. alabamensis and G. latidens were more coarsely serrated. Thurmond & Jones (1981) recognized the validity and occurrence of both G. clarkensis and G. alabamensis in Alabama and noted that the two species could be differentiated by the shape of their mesial cutting edge, with that on G. clarkensis being smoothly convex and that on G. alabamensis being straight, concave, or S-shaped. Manning & Standhardt (1986) later synonymized G. clarkensis with G. alabamensis , stating, with no justification, that the former were the upper teeth of the latter. This synonymy is in error, as the alabamensis morphology is more appropriately assigned to Physogaleus (see above).

An examination of high-resolution photographs of White’s (1956) syntypes leads us to believe that Galeocerdo clarkensis is a valid species that occurs within the Claiborne Group in Alabama. The holotype (NHMUK P.30501) measures 1.3 cm in height and 1.6 cm in mesiodistal width, proportions that suggests it is an anterior tooth. One of syntypes, NHMUK P.30467, measures 1.2 cm in height and 2.0 cm in mesiodistal width, suggesting it is a lateral tooth. The second syntype, NHMUK P.30502, is slightly ablated, but as preserved measures 0.7 cm in height and 1.3 cm in mesiodistal width, suggesting the tooth is from a lateroposterior position. All three of these teeth have compound serrations, an evenly convex mesial edge, and serrations that extend nearly to the apex on both the mesial and distal cutting edges. The presence of an evenly convex mesial edge on all three G. clarkensis syntypes indicates that this characteristic is consistent across the tooth row, separating this species from G. eaglesomei , whose anterior teeth have a mesial edge that is strongly sinuous. In addition, the development of compound serrations on the teeth of G. clarkensis is in contrast to G. eaglesomei , whose teeth have simple serrations. Our examination of Galeocerdo teeth from the Clinchfield Formation in Georgia, identified as G. alabamensis by Parmley & Cicimurri (2003), leads us to conclude that they are similar to the G. clarkensis teeth reported herein.

We could not confidently differentiate upper and lower teeth for this species. Monognathic heterodonty is expressed as anterior teeth that are nearly as tall as wide, and lateral teeth are much wider than tall with a more inclined cusp. Lateral teeth of G. clarkensis could be confused with the lateral teeth of Carcharhinus mancinae sp. nov., as both have convex mesial cutting edges and compound serrations. However, the distal notch on the teeth of C. mancinae sp. nov. is much less defined and the lingual root protuberance is much more pronounced and “pinched.”

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the basal Gosport Sand at sites ACl-4 and AMo-4, and the Gosport Sand at site ACh-21. Middle Bartonian, Zone NP17.

Galeomorphii indet.

Fig. 37

cf. “ Synechodus ” sp. – Clayton et al. 2013: fig. 2a.

Material examined

UNITED STATES OF AMERICA – Alabama • 1 isolated tooth; Claiborne Group ; SC 2012.47.32 .

Description

Tooth fragment consisting of the distal shoulder with three cusplets preserved. Cusplets cylindrical, distally directed, decrease in size laterally. Lingual face of cusplets lack ornamentation, and slight orolingual shelf visible. Labial face with very coarse, oblique ridges that extend from crown base but do not reach apices of cusplets. Labial edge of the crown base overhangs the root, which is incompletely preserved.

Remarks

The single tooth fragment in our sample was picked by one of the present authors (DJC) out of bulk matrix recovered directly from the basal Lisbon Formation (bed 2 of Copeland 1966) at site ACov-11. This specimen was originally figured, but not described, by Clayton et al. (2013) who referred the tooth to cf. “ Synechodus ” sp. Cappetta & Case (2016) contested this assignment, simply on the grounds that the specimen fell outside the youngest known occurrence of the family.

SC2012.47.32 possesses a unique combination of having multiple lateral cusplets, a small orolingual shelf, a labial crown face that overhangs the root, heavily folded enameloid ornamentation on the labial face ( Fig. 37A ), and a smooth lingual face ( Fig. 37B ). Additionally, SC2012.47.32 exhibits a third lateral cusplet, and the lateral two cusplets have a slight medial bend. This combination of characteristics separates this tooth fragment from all the other specimens in our sample and does conform well with the genera represented within the Paleospinacidae , including Palidiplospinax Klug & Kriwet, 2008 and Synechodus Woodward, 1888 (see Cappetta 2012: figs 304–6). Unfortunately, we scrutinized the specimen but cannot determine what taxon it represents due to its incompleteness, but it is included here for thoroughness.

Stratigraphic and geographic range in Alabama

The lone specimen in our sample, SC2012.47.32, was derived from the basal Lisbon Formation at site ACov-11. Middle Lutetian, Zone NP15.

Figures

Fig. 36. Galeocerdo clarkensis White, 1956, teeth. A–E. MSC 188.68, lateral tooth, basal Gosport Sand. A. Labial view. B. Close–up of distal notch. C. Lingual view. D. Close–up of mesial compound serrations. E. Mesial view. F–J. MSC 188.272, lateral tooth, basal Gosport Sand. F. Labial view. G. Close–up of mesial compound serrations. H. Lingual view. I. Close–up of distal notch. J. Mesial view. K–O. MSC 2382.4, lateral tooth, Gosport Sand. K. Labial view. L. Close–up of distal notch. M. Lingual view. N. Close–up of mesial serrations. O. Mesial view. P–T. MSC 37592, anterolateral tooth, basal Gosport Sand. P. Labial view. Q. Close–up of mesial compound serrations. R. Lingual view. S. Close–up of distal notch. T. Mesial view. Scale bars = 5 mm.

Fig. 37. Galeomorphii indet., tooth fragment. SC2012.47.32, basal Lisbon Formation. A. Labial view. B. Lingual view. C. Oral view. D. Basal view. Scale bar = 2 mm.