Orthacanthus

Orthacanthus is an extinct genus of fresh-water xenacanthiform cartilaginous fish, named by Louis Agassiz in 1843, ranging from the Upper Carboniferous into the Lower Permian. Orthacanthus had a nektobenthic life habitat, with a carnivorous diet. Multiple authors have also discovered evidence of cannibalism in the diet of Orthacanthus and of "filial cannibalism" where adult Orthacanthus preyed upon juvenile Orthacanthus. Synonyms of the genus Orthacanthus are Dittodus Owen, 1867, Didymodus Cope, 1883, Diplodus Agassiz, 1843, Chilodus Giebel, 1848 (preoccupied by Chilodus Müller & Troschel, 1844).

During the Late Carboniferous-Early Permian, Orthacanthus was an apex predator of freshwater swamps and bayous in Europe and North America. Mature Orthacanthus reached nearly 3 meters (10 feet) in length. Orthacanthus teeth have a minimum of three cusps, two principal cusps, and an intermediate cusp, where the principal cusps are variously serrated, with complex base morphology. Additionally, Orthacanthus can be diagnosed by major transverse axes of proximal ends at a 45-degree angle to and often almost parallel to the labial margin of the base between the cusps. Deformed teeth are characteristic of the xenacanthiform sharks and of Orthacanthus.