| Stethacanthus altonensis|
Fossil range: Late Devonian - Early Carboniferous
A pair of Stethacanthus altonensis.
| Scientific classification
Stethacanthus altonensis, like the other stethacanthid sharks, displayed conspicuous sexual dimorphism. Males had large spike-like denticles on top of head and the crest of the highly modified first dorsal fin. The fin and spine of S. altonensis are back-to-back upright triangles with the dorsal fin movably hinged to the rear margin of the spine by a tongue-in-groove joint. (The illustration of the spine is a redrafting of the original drawing of the type specimen). The spine itself was not movable, being mounted deep between the epaxial muscles. Females lacked the fin and the spine, as well as any scales at all.
It is likely from the fossil remains we have found in the Bear Gulch Bay that this bay may have been a pupping ground (nursery ground) for large stethacanthids as well as a stopover for feeding during migratory cruising.
Fossils of this species have been found in the U.S. (for example, in Montana and Ohio) and in Russia. Stethacanthus altonensis was about 4 feet long on the average. It had large cusped teeth and many pointed ones. Scales were present on the head and first dorsal find of males. Females apparently had few if any, scales. The tail had an almost symmetrical high aspect ratio. This shark lived in a span from the Upper Devonian to the Mississippian.
- Lund, R. 1974. "Stethacanthus altonensis (Elasmobranchii) from the Bear Gulch Limestone of Montana." Ann. Carnegie Museum 45: 161-178.
- Lund, R. 1985. "Stethacanthid elasmobranch remains from the Bear Gulch Limestone (Namurian E2b) of Montana." Amer. Mus. Nat. Hist. Novitates, 2828: 1-24.