the pelvic girdles have a metapterygial element supporting only one or two radials and most of the fin radials are attached directly to the pelvic plate. The derived condition differs in that there is a much higher number of radials supported by the pelvic plate. This feature, accompanied with a broadening of the pelvic girdle in order to accommodate the increased number of radials is a characteristic of Stethacanthus and other symmorriids. The males had claspers that were club-shaped at the distal ends and composed of non-prismatic globular calcified cartilage. Caudal fin There was some caudal fin variety among Stethacanthus species; while some had low angle heterocercal tails, some had tails approaching homocercal. The broad hypochordal lobe was supported by long, splayed fin radials. Paleobiology It is certain that Stethacanthus was a carnivore, and considering its small size probably fed on small fish, brachiopods, and crinoid ossicles like other sharks of its time. Additionally, as the spine-brush complex is rather a large structure, it seems likely that, in combination with the forward-facing denticles on the structure, it would have produced a drag force during fast locomotion. Therefore, Stethacanthus was probably a slow-moving shark. The fins of Stethacanthus were also smaller than in other sharks of the same size, and their teeth were also on the small side relative to other small Paleozoic sharks, suggesting that Stethacanthus may have been a bottom-dweller. Considering that most of the Stethacanthus specimens were recovered in the Bear Gulch Limestone in Montana, it is possible that this area was not only a breeding ground for other sharks but also for Stethacanthus, suggesting that they were migratory. History The several species of Stethacanthus discovered in the late 1800s were established based solely upon isolated spines, which initially confused paleontologist John Strong Newberry into thinking the spines constituted a new kind of fin. He originally believed that the spines were part of the pectoral fins and that they were not bilaterally symmetrical. Meanwhile, the first associated skeletal remains found in the Mississippian of Montana and the Devonian and Mississippian of Ohio remained undescribed for nearly a century. Since complete skeletons were extremely rare, Stethacanthus classification was vague and based on few characteristics. It was not until 1974 that the family Stethacanthidae was defined by Richard Lund because Stethacanthus differed so greatly from other Elasmobranchs of the time. Relative classifications of symmoriids compared to stethacanthids are still debated.