In modern oceans, the carcharhinids (requiem sharks) are one of the largest families and the dominant shark of tropical waters. The family dates to the Early Palaeocene (Danian) and Abdounia is one of its early members. In the Nanjemoy (Ypresian, Early Eocene) of Virginia, at least in the study area, the teeth of this genus, as represented by Abdounia cf beaugei, are the most common shark teeth by a wide margin. A. cf beaugei teeth appear at the base of the formation, at its contact with the Marlboro Clay (Palaeocene) and Ward & Weist (1990) notes its presence Aquia (Palaeocene).
The teeth of the genus are small, although Cappetta (1987: 120) notes them reaching nearly 1.5 cm in height. Describing teeth of the genus, he notes that the cusp is triangular and the enameloid usually smooth. The cusp of anterior teeth is upright, becoming more distally directed moving towards the commissure. The anterior teeth usually have a pair of cusplets and anterio-laterals, up to three on each shoulder. Lateral teeth usually loose the mesial cusplets and posteriors are generally left with a single distal cusplet. The crown does not overhang the root, which has a strong nutrient groove.1
The genus includes inpart:
Abdounia africana (ARAMBOURG, 1952) Danian-Thanetian (Palaeocene), Morocco
A. beaugei (ARAMBOURG, 1935) Palaeocene - Eocene, North Africa, Europe & North America
A. enniskilleni (WHITE, 1956) Eocene of Alabama & Georgia
A. furimskyi (CASE 1980) Upper Eocene of North Carolina
A. lapierrei CAPPETTA & NOLF 1981 Eocene, France & No America
A. minutissima (WINKLER 1873) Eocene of England & Belgium and
A. recticona (WINKLER 1873) Eocene, Europe & North America
Kent (1994) listed three Chesapeake region species:
Abdounia beaugei, distinguished by its broad triangular cusplets; from the Aquia (Palaeocene), Nanjemoy & Piney Point (Eocene) Formations,
A. recticona, a larger tooth with five to eight reduced cusplets; Nanjemoy & Piney Point Formations, and
A. lapierrei, characterized by its slender cusp and cusplets; Piney Point Formation.
Case (1994) reported two species from Late Palaeocene - Early Eocene sediments of Mississippi,
Abdounia beaugei and
A. subulidens (ARAMBOURG, 1952) which he noted as possibly synonymous with A. minutissima.
In addition to A. cf beaugei, the Nanjemoy yields a second (undescribed), but still common, Abdounia species. These teeth are best characterized by their mesial cusplet which is much reduced. David Ward refers to them as being wide and low-crowned, with double lateral cusplets only in the most lateral files. He notes that Casier called them Scyliorhinus minutissimus but the Ypresian examples from Virginia are much different than those Lutetian teeth.
Fabrice Moreau (pers com 2006) notes that the Nanjemoy "beaugei" teeth are smaller than their European/North African counterparts and more often have multiple lateral cusplets.
Not found in the Potapaco Bed A and B sands of Stafford Co., Virginia are the teeth of A. recticona which have been found in other Ypresian faunas, including the Woodstock Member of the Nanjemoy in Charles Co., MD, Piney Point Formation of Hanover Co., VA and Castle Hayne Fm. of NC.
|1||The Muddy Creek specimens fail to follow some of these general characteristics - one species usually lacks a mesial cusplet and an another has two pairs of cusplets through most of the upper file. It would appear that the genus has greater diversity than previously suspected.|
Selected References (additional in Bibliography)
Cappetta, H., 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology, 3B. Gustav Fischer Verlag, Stuttgart and New York, 193 pp.
Case, G., 1994. Fossil Fish Remains fron the Late Paleocene Tuscahoma and Early Eocene Bashi Formations of Meridian, Lauderdale County, Mississippi. Palaeontographica Abt. A, 230, pp 97-138.
Kent, B., 1994. Fossil Sharks of the Chesapeake Region. Egan Rees & Boyer, Maryland. 146 pp.
Ward, D & Weist, R., 1990.A checklist of Paleocene and Eocene sharks and rays (Chondrichthyes) from the Pamunkey Group, Maryland and Virginia, USA. Tertiary Res., 12(2) p 81-88.