Orestiacanthus fergusi
Orestiacanthus fergusi is a member of the cladodontid elasmobranch family Stethacanthidae. They range to about 25-28 cm in length.
As in other Stethacanthidae, they have a highly modified first dorsal fin-spine complex as well as enlarged scales on the dorsal surface of the head. The dorsal fin-spines of males are intermediate in morphology between the spines of Stethacanthus altonensis and Damocles serratus. (See left.)
Males have a complete complement of placoid scales, but females only have scales along the pectoral fin axis and a short strip of scales that extend along the lateral line canal from the shoulder girdle. The fins were thick and well muscled, most likely with significant fin membrane extending beyond the endoskeletal elements. They were generalized swimmers, with the well-developed cladodont pectoral axis presumably functioning for fine maneuvering control, chemical sensing, or both.
Orestiacanthus has the small homodont cladodont (piercing) teeth of a 2nd order predator.
Sexual dimorphism:
In contrast to other known stethacanthids, the males are completely scaled, while the females preserve with limited squamation, particularly along the pectoral axis. There are several species similar to O. fergusi that are known only by spines, from the midcontinental U.S.A
Reference:
- Lund, R. 1984. "On the spines of the Stethacanthidae (Chondrichthyes), with a description of a new genus from the Mississippian Bear Gulch Limestone." Geobios, 17, fasc. 3: 281-295.