Gli squali fossili
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 Paleocene (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 beaugei, are the most common shark teeth by a wide margin. A. beaugei teeth appear at the base of the formation, at its contact with the Marlboro Clay (Paleocene) and Kent (1994) notes its presence Aquia (Paleocene).
The teeth of the genus are small, although Cappetta (1987) 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 commisure. 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.
The genus includes: Abdounia africana (ARAMBOURG, 1952) Danian-Thanetian (Paleocene), Morocco A. beaugei ARAMBOURG Paleocene - 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. 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 (Paleocene), 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 Paleocene - 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. 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.
Not found in the Potapaco Bed A and B sands of Stafford Co., Virginia teeth of A. recticona have been found in other Ypresian faunas, including the Woodstock Member of the Nanjemoy in Charles Co., MD and the Piney Point Formation of Hanover Co., VA.
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