Otodus (Carcharocles)

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 : 28-30

Otodus (Carcharocles) sp.

Fig. 9 M–X

Squalus auriculatus de Blainville, 1818: 80 .

Carcharodon auriculatus – Agassiz 1843: 254 , pl. 28, figs 17–19.

Procarcharodon auriculatus – Casier 1960: 13 .

Carcharocles auriculatus – Keyes 1972: 237 .

Otodus (Carcharocles) auriculatus – Cappetta 2012: 224 , fig. 209.

Material examined

UNITED STATES OF AMERICA – Alabama • 23 isolated teeth; Claiborne Group ; ALMNH PV1985.87.7, ALMNH PV1985.87.8, ALMNH PV1988.29.1, ALMNH PV1989.4.50.2, ALMNH PV1992.28.44.1–2, ALMNH PV 2016.4.27 (2 specimens), ALMNH PV 2016.4.28 (3 specimens), ANSP 23410 , ANSP 23411 , ANSP 23412 , MMNS VP-8233, MSC 2370 , MSC 2371 , MSC 37019, MSC 37158, MSC 37170, MSC 37172, MSC 37288, NJSM 24021 .

Description

Teeth very large, approaching 10 cm in overall height. Main cusp large, robust, triangular, flanked by a single pair of lateral cusplets. Anterior teeth with erect main cusp; whereas main cusp on lateral teeth broader, lower, with slight distal inclination. Base of main cusp broader on upper anterior teeth than in lower anterior files. Lingual crown face smooth and strongly convex; labial face smooth and nearly flat to moderately convex. Prominent V-shaped dental band present at lingual base of main cusp. Lateral cusplets broad and triangular, variable in overall height and width. Cutting edges of main cusp and lateral cusplets serrated from the base to the apex. Serrations coarse, often varying from regular to irregular along the length of the cutting edge, decreasing in size apically to crown apex. Root robust with well-developed lingual protuberance. Multiple prominent foramina present on lingual root face. Root lobes slightly divergent, with U-shaped or V-shaped interlobe area.

Remarks

The generic placement of teeth with this morphology has been a contentious subject for many years, with the names Squalus Linnaeus, 1758 , Carcharodon Smith in Müller & Henley, 1838 , Procarcharodon Casier, 1960 , Carcharocles Jordan & Hannibal, 1923, and Otodus Agassiz, 1843 each being used by various researchers (see Agassiz 1843; Jordan & Hannibal 1923; Glikman 1964; Cappetta 1987, 2012; Applegate & Espinosa-Arrubarrena 1996; Zhelezko & Kozlov 1999; Purdy et al. 2001; Nyberg et al. 2006; Pimiento et al. 2010; Ehret et al. 2012; Pimiento et al. 2013; Ehret & Ebersole 2014). It is believed that this genus is part of an evolutionary lineage that begins with Otodus (Otodus) obliquus and culminates with Otodus (Megaselachus) megalodon (see Cappetta 2012; Ehret et al. 2012; King et al. 2013; Malyshkina & Ward 2016). Cappetta (2012) suggested the usage of Otodus for all specimens within this lineage and assigned unserrated teeth with cusplets to the subgenus Otodus (Otodus) , those with serrated crowns and cusplets to Otodus (Carcharocles) , and those with serrations and no cusplets to Otodus (Megaselachus) . We follow the recent convention and utilize Cappetta’s (2012) taxonomic divisions for the members of Otodonitdae, with Otodus (Otodus) representing unserrated species and Otodus (Carcharocles) the serrated species with lateral cusplets.

Taxonomic uncertainty clouds accurate identification of large serrated teeth like those from the Claibornian of Alabama, as numerous nominal Otodus (Carcharocles) species have been named from Eocene deposits elsewhere ( Cappetta 2012). Early-to-middle Eocene teeth like those described above have been assigned to O. (C.) angustidens (Agassiz, 1843) , O. (C.) auriculatus ( de Blainville, 1818) and O. (C.) sokolovi ( Jaekel, 1895) , based on tooth size and the nature of serrations. It is unclear, however, if these morphologies represent distinct species because the range of variation within each taxon is insufficiently documented, and type descriptions and figures are far from adequate when differentiating specimens. Agassiz (1843), for example, admitted that he lacked specific characteristics to separate his C. angustidens type specimens from C. auriculatus , and did so based on tooth size. Case & Cappetta (1990) noted that the teeth of C. auriculatus differed from those of C. sokolovi by having serrations that are stronger and more irregular, by having lateral cusplets that are more united to the main cusp, and by having root lobes that are more mesiodistally compressed. However, these characteristics are highly variable on the teeth in our Claiborne sample, and they co-occur within the Priabonian Parkers Ferry Formation of South Carolina (DJC, pers. observ.). Diedrich (2013) and Malyshkina & Ward (2016) reported both the auriculatus and sokolovi morphologies as coeval, and these occurrences suggest that 1) two very similar species of large shark inhabited the same paleoenvironment, or 2) the tooth morphologies represent variation within a single biological species. It is entirely possible that the small teeth Diedrich (2013) identified as O. (C.) auriculatus represent the same species as large teeth he identified as O. (C.) sokolovi . Due to the variability in tooth morphology and limited sample size among the Claibornian units, we refrain from making specific determinations for these specimens. However, we utilize the subgenus Carcharocles to differentiate these serrated Otodus teeth from unserrated Otodus (Otodus) .

Stratigraphic and geographic range in Alabama

Specimens in our sample were collected from the contact of the Tallahatta and Lisbon formations at sites ACov-11, ACh-14, and ACon-6, the basal Lisbon Formation at site ACov-11, and the Gosport Sand at site ACh-21. Lower Lutetian to middle Bartonian, zones NP14 to NP17.

Family Mitsukurinidae Jordan, 1898

Figures

Fig. 9. Otodontidae Glikman, 1964, teeth. A–L. Otodus (Otodus) sp. A–C. MSC 2999.2, lower Tallahatta Formation. A. Labial view. B. Lingual view. C. Mesial view. D–F. MSC 3008.1, lower Tallahatta Formation. D. Labial view. E. Lingual view. F. Mesial view. G–I. MSC 35761.2, lower Tallahatta Formation. G. Labial view. H. Lingual view. I. Mesial view. J–L. MSC 35761.1, lower Tallahatta Formation. J. Labial view. K. Lingual view. L. Mesial view. — M–X. Otodus (Carcharocles) sp. M–O. MSC 37019, basal Lisbon Formation, courtesy of Carl Sloan. M. Labial view. N. Lingual view. O. Distal view. P–R. MSC 37172, basal Lisbon Formation, courtesy of James Lowery. P. Labial view. Q. Lingual view. R. Mesial view. S–U. MSC 2371, Gosport Sand. S. Labial view. T. Lingual view. U. Mesial view. V–X. MSC 2370, Gosport Sand. V. Labial view. W. Lingual view. X. Distal view. Scale bars: A–F, M–X =1 cm; G–L=5 mm.