Palaeocybium proosti ( Storms, 1897 )

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 : 173-175

Palaeocybium proosti ( Storms, 1897)

Fig. 64 A–I

Cybium proosti Storms, 1897: 242 , figs 1–2.

Cybium proosti – Leriche 1905: 79 , 150, 192, pl. 10, fig. 2.

Cybium sp. – Case 1981: 2, fig. 17.

Cybium proosti – Case 1986: 6 , figs 10–11.

Acanthocybium proosti – Weems 1999: 66 , pl. 4.6, fig. g.

Palaeocybium proosti – Monsch 2005: 460 .

Material examined

UNITED STATES OF AMERICA – Alabama • 6 isolated teeth; Claiborne Group; ALMNH PV1989.4.130, MSC 37423, MSC 38433, MSC 38500.1–2, MSC 37194.4.

Description

Teeth lanceolate, measuring up to 6.15 mm in height. Anterior and posterior carinae sharp, smooth, convex; carinae extend to tooth base, form rounded apex. Labial and lingual faces bi-convex, of equal dimension, smooth. Tooth base slightly thickened, with deep pulp cavity.

Remarks

The specimens in our sample compare well to Palaeocybium proosti ( Storms, 1897) teeth reported from Europe and North America (see Casier 1946; Kemp et al. 1990; Weems 1999). Palaeocybium proosti was originally placed within Cybium , a genus that is now regarded as a junior synonym of Scomberomorus Lacépède, 1802 (see Bannikov 1982; Collette 2003). Weems (1999) placed this morphology within Acanthocybium Gill, 1862 based on two partial dentaries from the Nanjemoy Formation in Virginia, suggesting it was a primitive species within the genus. Monsch (2005) later noted that Storms’ (1897) type specimen has two rows of teeth on the dentary, an inner and outer, which is a characteristic that distinguishes the proosti morphology from the dentitions of Acanthocybium and Scomberomorus . As a result, Monsch (2005) placed the proosti species within a new genus, Palaeocybium .

Teeth of Palaeocybium are conspicuously thicker than morphologically similar teeth of Sphyraena (see above), and they have a larger and deeper pulp cavity. The Palaeocybium teeth in our sample were differentiated from those of Scomberomorus (see below) by having carinae that extend to the base of the teeth, they have a symmetrical basal outline (with carinae visible) and are not basally constricted.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the contact of the Tallahatta and Lisbon formations at site ACov-11, 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. 64. Palaeocybium proosti (Storms, 1897) and Scomberomorus Lacépède, 1802, teeth. A–I. Palaeocybium proosti A–C. MSC 37194.4, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. A. Lingual view. B. Carinal view. C. Basal view. D–F. MSC 37423, basal Gosport Sand. D. Lingual view. E. Carinal view. F. Basal view. G–I. MSC 38500.2, basal Gosport Sand. G. Lingual view. H. Carinal view. I. Basal view. — J–R. Scomberomorus bleekeri (Storms, 1892). J–L. MSC 37147, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. J. Lingual view. K. Carinal view. L. Basal view. M–O. MSC 35777.2, basal Gosport Sand. M. Lingual view. N. Carinal view. O. Basal view. P–R. MSC 37268.1, basal Lisbon Formation. P. Lingual view. Q. Carinal view. R. Basal view. — S–AA. Scomberomorus stormsi (Leriche, 1905). S–U. MSC 37512.1, basal Gosport Sand. S. Lingual view. T. Carinal view. U. Basal view. V–X. MSC 37126, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. V. Lingual view. W. Carinal view. X. Basal view. Y–AA. MSC 38974.1, lower Tallahatta Formation. Y. Lingual view. Z. Carinal view. AA. Basal view. Scale bars = 2 mm.