Negaprion gilmorei ( 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 : 73-77

Negaprion gilmorei ( White, 1956)

Fig. 27

Sphyrna gilmorei Leriche, 1942: 47 , pl. 4, fig. 1.

Alopias latidens alabamensis White, 1956: 132–133 , text figs 28–32, pl. 2, figs 5–6.

Negaprion gibbesi gilmorei White, 1956: 142 , figs 37–66, pl. 2, fig. 9.

Hypoprion greyegertoni White, 1956: 137 , figs 50–56, pl. 2, fig. 7.

Aprionodon greyegertoni – Thurmond & Jones 1981: 65 , fig. 30.

Negaprion gibbesi gilmorei – Thurmond & Jones 1981: 66 , fig. 31.

Carcharhinus greyegertoni – Kruckow & Thies 1990: 51 .

Carcharhinus gilmorei – Müller 1999: 49 , pl. 7, fig. 1.

Sphyrna sp. – Cappetta & Case 2016: 61, pl. 10, figs 1–4.

Material examined

UNITED STATES OF AMERICA – Alabama • 1519 isolated teeth; Claiborne Group ; ALMNH PV1989.4.13.3 (25 specimens), ALMNH PV1989.4.151.1b, ALMNH PV1989.4.193, ALMNH PV1989.4.196 (21 specimens), ALMNH PV 1989.4.6 (2 specimens), ALMNH PV1989.4.8.3 (17 specimens), ALMNH PV1989.4.8.4 (18 specimens), ALMNH PV1993.2.401 (160 specimens), ALMNH PV1993.2.402 (50 specimens), ALMNH PV2016.3.72, ANSP 23422 , GSA-V701 (5 specimens), GSA-V704 (2 specimens), GSA-V710, MSC 188.3 – 5 , MSC 188.7 – 10 , MSC 188.14 , MSC 188.24 – 25 , MSC 188.28 , MSC 188.30 , MSC 188.33 , MSC 188.35 , MSC 188.37 , MSC 188.46 – 48 , MSC 188.52 – 53 , MSC 188.55 – 59 , MSC 188.61 , MSC 188.63 – 64 , MSC 188.66 , MSC 188.69 – 71 , MSC 188.74 – 77 , MSC 188.80 – 81 , MSC 188.83 – 87 , MSC 188.90 – 93 , MSC 188.95 , MSC 188.97 – 100 , MSC 188.102 – 103 , MSC 188.105 – 106 , MSC 188.108 – 110 , MSC 188.113 – 116 , MSC 188.118 – 119 , MSC 188.122 , MSC 188.125 , MSC 188.127 , MSC 188.132 – 135 , MSC 188.137 – 139 , MSC 188.141 – 144 , MSC 188.146 – 148 , MSC 188.150 , MSC 188.152 – 157 , MSC 188.160 – 163 , MSC 188.165 , MSC 188.167 – 168 , MSC 188.170 – 173 , MSC 188.175 , MSC 188.177 , MSC 188.180 – 184 , MSC 188.186 – 187 , MSC 188.189 – 192 , MSC 188.194 – 196 , MSC 188.198 – 201 , MSC 188.203 , MSC 188.206 , MSC 188.208 – 216 , MSC 188.218 – 224 , MSC 188.226 – 232 , MSC 188.234 – 240 , MSC 188.242 – 244 , MSC 188.246 – 253 , MSC 188.256 – 257 , MSC 188.260 , MSC 188.264 – 265 , MSC 188.267 , MSC 188.269 – 271 , MSC 188.274 , MSC 188.277 , MSC 188.279 , MSC 188.281 , MSC 188.284 – 291 , MSC 188.293 – 296 , MSC 188.298 – 302 , MSC 188.304 , MSC 188.306 , MSC 188.309 , MSC 188.312 – 315 , MSC 188.319 – 322 , MSC 188.325 , MSC 188.327 , MSC 188.329 , MSC 188.332 – 336 , MSC 1424.3 – 8 , MSC 1424.13 – 21 , MSC 2171.7 , MSC 2173.8 , MSC 2175.1 – 4 , MSC 2175.7 – 8 , MSC 2175.10 – 16 , MSC 2175.18 , MSC 2175.20 , MSC 2175.23 – 24 , MSC 2175.26 – 29 , MSC 2175.31 – 37 , MSC 2175.41 – 48 , MSC 2175.50 – 54 , MSC 2175.56 , MSC 2175.58 – 63 , MSC 2175.65 – 69 , MSC 2175.71 – 73 , MSC 2380.1 – 19 , MSC 37161.1 – 16 , MSC 37395, MSC 37431, MSC 37466.1 – 62 , MSC 37469, MSC 37475, MSC 37493.1 – 552 , MSC 37526.1 – 2 , MSC 37539.1 – 3 , MSC 37545, MSC 37593, MSC 37594, MSC 37596.1 – 134 , MSC 37597.1 – 6 , MSC 37649, MSC 37682.1 – 5 , MSC 37914.1 – 5 , MSC 37916.1 – 2 , MSC 38415.1 – 6 , MSC 38429, MSC 38465, MSC 38466.1 – 29 , MSC 38495.1 – 6 , MSC 38506.1 – 11 , MSC 38508.1 – 10 , MSC 38547.1 – 33 , MSC 38547.9 , MSC 38556.1 – 8 , NJSM 24029 , SC 2012.47.165 (4 specimens), SC 2012.47.176, SC 2012.47.181 .

Description

Dentition exhibits strong dignathic heterodonty. Upper anterior teeth with triangular main cusp. Broadbased cusp flanked by short, oblique mesial and distal heels. Lateral teeth mesiodistally wider, cusp distally inclined, shoulders more elongated, becoming horizontal. Posterior teeth wide, short and distally inclined cusp. Cutting edges on cusp smooth; cutting edges on shoulders smooth to weakly and irregularly serrated. Labial crown face flat; lingual face convex; smooth enameloid. Root bilobate; lobes elongated, low, rounded, highly diverging. Interlobe area generally shallow, V-shaped. Attachment surface of lingual face generally flat, bisected by deep nutritive groove. Nutritive groove often forms a distinctive basal notch. Lower anterior teeth with narrow, erect cusp flanked by short, nearly horizontal mesial and distal shoulders. Lateral teeth mesiodistally wider, with distally inclined cusp, elongated lateral shoulders. Posterior teeth with shorter and very inclined cusp. Cutting edges of cusp and shoulders smooth.

Remarks

Woodward (1889) erected the name Carcharias (Aprionodon) gibbesii for 120+ teeth he examined in the NHMUK collections that were derived from Eocene deposits in South Carolina and Clarke County, AL. Although Woodward (1889) did not figure these teeth, with some uncertainty he referred several of those illustrated by Gibbes (1848) to his new taxon, whereas others he identified as Galeocerdo minor Agassiz, 1843 ( Gibbes 1848: pl. 25, figs 63–65), and a single specimen was assigned to Oxyrhina minuta Agassiz, 1843 ( Gibbes 1848: pl. 27, fig. 164).

White (1956) later reexamined Woodward’s (1889) Carcharias (Aprionodon) gibbesii teeth and agreed that Gibbes’ (1848: pl. 27, fig. 164) Oxyrhina minuta was a lower tooth of the gibbesii morphology. However, of Gibbes’ (1848: pl. 25, figs 63–65) Galeocerdo minor teeth, White (1956) disagreed with Woodward’s (1889) referral and said they belonged instead to Sphyrna prisca (Agassiz, 1843) . White (1956) assigned the gibbesi morphology to Negaprion because he believed that they more closely resembled teeth of the extant Lemon Shark. However, several years prior, Leriche (1942: 47, pl. 4, fig. 1) figured two teeth from the Priabonian Yazoo Clay at Cocoa in Choctaw County, AL that he referred to a new taxon, Sphyrna gilmorei , noting their similarity with the extant Sphyrna prisca . White (1956) reexamined these teeth and synonymized S. gilmorei with Negaprion gibbesii . White (1956) also noted slight differences between Woodward’s (1889) South Carolina and Alabama teeth and stated that the South Carolina specimens had finer serrations on the upper teeth, and to some extent on the lower teeth, whereas the lower teeth from Alabama were smooth. Because of this, White (1956) referred to the South Carolina teeth as the “typical” form Negaprion gibbesii , and assigned the Alabama teeth to a new subgenus, Negaprion gibbesii gilmorei . White’s (1956) placement of these morphologies within Negaprion was later followed by numerous authors, including Case (1980), Thurmond & Jones (1981), Westgate (1984), and Krukow & Thies (1990).

Based on nine teeth from Clarke County, AL, White (1956) erected the taxon Hypoprion greyegertoni , which Thurmond & Jones (1981) later placed within Aprionodon because this genus lacked the lateral cusplets that occur on the teeth of Hypoprion . Thurmond & Jones (1981) also stated that the teeth of Aprionodon greyegertoni were very similar to those of Negaprion gibbesi gilmorei but differed by being taller than broad and lacking a medial nutritive groove (stating this characteristic was very prominent on the teeth of N. gibbesi gilmorei ). Müller (1999), however, noted issues with White’s (1956) H. greyegertoni syntypes and believed that they represented at least three different genera. Müller (1999) designated H. greyegertoni as a nomen dubium, referred most of White’s (1956) syntypes to the genera Abdounia and Physogaleus , and assigned White’s (1956: figs 50–51, 53–54, 56) remaining teeth to the gilmorei morphology.

Ward & Wiest (1990) and Müller (1999) both recognized teeth of the gibbesi morphology as occurring within the Paleocene-to-Eocene Pamunky Group in Maryland, and Müller (1999) reported both the gibbesi and gilmorei morphologies from the same deposits in Virginia. Ward & Wiest (1990) and Müller (1999) placed these morphologies within the genus Carcharhinus , and between the two, elevated both C. gibbesi and C. gilmorei to species status. Manning (2003) later suggested that these two species are intergradational, with C. gilmorei occurring in both Eocene and Oligocene deposits, whereas C. gibbesi was largely confined to the Oligocene.

As part of our study, we examined numerous teeth of the gilmorei / gibbesi morphologies that were derived from various middle Eocene (Lutetian) to late Oligocene (Chattian) localities in Alabama. We determined that all these teeth represent the gilmorei morphology, as serrations on the upper and lower teeth were either absent or inconspicuous.Although no teeth attributable to the gibbesi morphology (those with distinct heel serrations) were identified in our sample, the presence of the gilmorei morphology within both Eocene and Oligocene deposits in Alabama corroborates Manning’s (2003) observation regarding the stratigraphic range of this species.

To further complicate the matter, Cappetta & Case (2016) identified 40 specimens from the contact of the Tallahatta and Lisbon formations at site ACov- 11 in Covington County as belonging to Sphyrna sp. and suggested these teeth represented the oldest occurrence of this genus. Cappetta & Case (2016: pl. 10, figs 1–4), however, failed to compare the teeth in their sample to those with the gilmorei morphology, even though the specimens they figured are conspecific with the upper teeth of this taxon. Furthermore, our sample consisted of 23 additional specimens from the ACov-11 locality that appear conspecific to those figured by Cappetta & Case (2016), all of which are consistent with the gilmorei morphology.

Confusion over the generic placement of teeth with the gilmorei morphology stems from the generalized dentition of this shark, which consists of T-shaped lower teeth and upper teeth with a broader triangular main cusp.This generalized dentition strongly resembles those of several representatives within the extant Carcharhinus , Negaprion , and Sphyrna , prompting various authors, at one point or another, to refer the gilmorei morphology to each of these genera (see Leriche 1942; White 1956; Müller 1999). To garner insight into the taxonomic placement of teeth with the gilmorei morphology, we compared the teeth in our sample to those within the dentitions of extant representatives within all three of the aforementioned genera. Our observations show that the dentitions of the numerous species of Carcharhinus are extremely variable in terms of upper and lower tooth morphology, but all members of the genus can be categorized by having distinct dignathic heterodonty with upper teeth having serrated mesial and distal cutting edges, and lower teeth with more slender crowns that may or may not have weak serrations (see Voigt & Weber 2011). A few Carcharhinus species have lower teeth that bear fine serrations extending nearly to the apex of the crown (i.e., C. acronotus , C. albimarginatus , C. amblyrhynchos , C. amboinensis , C. borneensis , C. brachyurus , C. leucas , C. longimanus , and C. wheeleri ), whereas other species have weak serrations that are confined to the mesial and distal shoulders (i.e., C. hemiodon , C. obscurus , C. porosus , C. signatus ). However, the upper teeth of all these species have serrated mesial and distal cutting edges, with serrations generally extending nearly to the crown apex.

The Sphyrnidae ( Eusphyra and Sphyrna ) jaw sets we examined exhibited varying degrees of dignathic heterodonty (see Compagno 1984) and fall into one the following four categories: 1) those with triangular upper teeth and lower teeth with a narrow crown and a sinuous mesial edge (i.e., Eusphyra blochii and Sphyrna tiburo ); 2) those with upper and lower teeth with a narrow crown and a sinuous mesial edge (i.e., Sphyrna corona ); 3) those with triangular upper teeth and T-shaped lower teeth (i.e., Sphyrna lewini , Sphyrna media , and Sphyrna tudes ); and 4) those with triangular upper and lower teeth exhibiting little dignathic heterodonty (i.e., Sphyrna mokarran and Sphyrna zygaena ). Of these species, S. tudes had serrated cutting edges on its upper teeth but smooth cutting edges on the crowns of lower teeth, and upper and lower teeth of S. mokarran are uniformly serrated. All remaining species have upper and lower teeth that lack serrations.

The dentitions of the two extant species of Negaprion , N. acutidens and N. brevirostris , exhibit a similar degree of dignathic heterodonty, consisting of triangular upper teeth and T-shaped lower teeth. Both species also have serrated upper teeth, although to varying degrees. The upper teeth of N. acutidens have serrated mesial and distal cutting edges, and the serrations extend almost to the cusp apex. In contrast the serrations on upper teeth of N. brevirostris are confined to the mesial and distal shoulders and do not extend onto the central cusp. The cutting edges on the lower teeth of both species are smooth. Examination of teeth from the extinct N. eurybathodon show they are more similar to those of N. brevirostris , with a difference being the occasional presence of weak serrations on the mesial and distal shoulders on certain lower teeth of the extinct species.

Although early Carcharhinus representatives have been recently described from middle and upper Eocene deposits elsewhere (see Adnet et al. 2007; Underwood & Gunter 2012; Samonds et al. 2019), these species, as well as all the extant species, have upper teeth with serrations on their mesial and distal cutting edges that extend nearly to the apex of the crown. The presence of these mesial and distal serrations appears to be a defining characteristic of Carcharhinus (see Underwood & Gunter 2012), suggesting teeth with the gilmorei morphology do not belong to this genus. Assigning the gilmorei morphology to Sphyrna is also problematic because molecular divergence estimates by Lim et al. (2010) indicated that the family Sphyrnidae split from Carcharhinus during the early-to-middle Eocene (40 to 50 Ma), and that Sphyrna only diverged from its sister taxon Eusphyra during the early-to-middle Miocene (15 to 20 Ma). These data suggests that true members of Sphyrna did not evolve until the earlyto-middle Miocene, and any Eocene teeth with a similar morphology should therefore be referred to a different genus. Regarding the use of Negaprion, Schultz et al. (2008) calculated molecular divergence times for the two extant species of the genus and suggested that they are derived from a cosmopolitan common ancestor, the Oligo–Miocene Negaprion eurybathodon (Blake, 1862) .

Our analysis showed that extant species of Carcharhinus , Sphyrna tudes , and Negaprion acutidens have teeth with serrations that extend nearly to the apex of the crown in all upper tooth positions. In addition, all the species within the Sphyrnidae (with the exception of S. tudes and S. mokarran ) were observed to have smooth crowns on both the upper and lower teeth. Based on these observations, teeth with the gilmorei morphology appear most closely aligned with those of N. brevirostris and N. acutidens in that they have triangular upper teeth, T-shaped lower teeth, and weak serrations that are limited to the mesial and distal shoulders of certain teeth (as serrations appear on the upper teeth in N. brevirostris and both upper and lower teeth in N. acutidens ). Due to their morphological similarity to the other members of Negaprion , we concur with previous assignments of the gilmorei morphology to Negaprion , making N. gilmorei one of the earliest representatives of the genus.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the contact of the Tallahatta and Lisbon formations at sites ACh-14, ACov-11 and ACon-6, the basal Lisbon Formation at site ACov-11, the “upper” Lisbon Formation at site ACl-3, the contact of the Lisbon Formation and Gosport Sand at site AMo-4, the basal Gosport Sand at site ACl-4, and the Gosport Sand at site ACh-21. Lower Lutetian to middle Bartonian, zones NP14 to NP17.

Figures

Fig. 27. Negaprion gilmorei (White, 1956), teeth. A–C. MSC 37682.2, upper lateral tooth, basal Lisbon Formation. A. Labial view. B. Lingual view. C. Mesial view. D–F. MSC 37596.132, lower anterolateral tooth, basal Gosport Sand. D. Labial view. E. Lingual view. F. Mesial view. G–I. MSC 38466.2, upper lateral tooth, basal Gosport Sand. G. Labial view. H. Lingual view. I. Mesial view. J–L. MSC 38466.1, upper lateral tooth, basal Gosport Sand. J. Labial view. K. Lingual view. L. Mesial view. M–O. MSC 37596.5, lower anterior tooth, basal Gosport Sand. M. Labial view. N. Lingual view. O. Mesial tooth. P–R. MSC 37596.116, upper lateral tooth, basal Gosport Sand. P. Labial view. Q. Lingual view. R. Mesial view. S–U. MSC 37596.11, upper lateral tooth, basal Gosport Sand. S. Labial view. T. Lingual view. U. Mesial view. V–X. MSC 37596.121, upper lateral tooth, basal Gosport Sand. V. Labial view. W. Lingual view. X. Mesial view. Scale bars = 5 mm.