of the head has its own collection of denticles which point posteriorly. The presence of these large denticles has led to theories that the spine-brush complex in combination with the denticles on the head was used to scare away predators by simulating the mouth of a larger fish. The complex has been affirmed only in males, and only in those males that have reached sexual maturity. Whether the complex was present in females of the species is still unknown. Another theory for the spine-brush complex is that it was involved either in attracting a mate or in the mating process itself. Pectoral fin whip The pectoral fins of Stethacanthus were composed of the triangular-shaped metapterygium observed in modern-day sharks, but had an additional long, metapterygial structure called a fin whip. These fin whips contain at least 22 axial cartilages and extended past the pelvic fins. The three most anterior axials are shorter than the more posterior axials. The purpose of the fin whips is unknown but it has been suggested that they were used during mating. Teeth and denticles The tooth files are whorl-shaped and the palatoquadrate is scalloped with 6-7 recesses to allow for the tooth families. The individual teeth are widely separated from each other in the tooth whorls. The teeth themselves are of the cladodont variety; the bases of the teeth are broadest on the lingual side, and each support a single large cusp and two pairs of smaller accessory cusps for a total of five cusps. The medial and most lateral cusps are the most fluted. The teeth appear to be mostly orthodentine, but when viewed in cross-section, change abruptly to osteodentine. The enameloid is single-layered, overlaying the thick mantle of orthodentine. In addition to the dentition teeth, there are also a number of buccopharyngeal denticles lining the oropharynx. The denticles lining the top of the head and the top of the spine-brush complex are larger than the dentition teeth, and they appear as elongate monocuspid denticles. Pelvic girdles and claspers In Stethacanthus, the pelvic girdles consist of sheets of prismatic cartilage, each in the shape of a subtriangular, rounded plate. The anterior edge of each girdle is slightly concave while the posterior is convex. There appears to be no union of the two plates. There are two types of pelvic girdles found in stethacanthids: the primitive condition and the derived condition. In the primitive condition,