page_title: Orthacanthus
section_title: Classification
hierarchical_section_title: Orthacanthus / Historical information and discovery / Classification
caption_attribution_description: English: Fragmented orthacanthus teeth from the Halgaito shale of Arizona, USA, showing typical crescent-shaped bicuspids. photo by me user debivort October 2007
context_page_description: Orthacanthus is an extinct genus of fresh-water xenacanthid sharks, named by Louis Agassiz in 1836, ranging from the Upper Carboniferous until the Lower Permian. Orthacanthus lived in marine environments and had a nektobenthic life habitat, with a carnivorous diet. Multiple sources have also discovered evidence of cannibalism in the diet of Orthacanthus and of "filial cannibalism" where adult Orthacanthus preyed upon juvenile Orthacanthus. The genus Orthacanthus has been synonymized with Dittodus, Didymodus, and Diplodus.
  About 260 million years ago, Orthacanthus was the apex predator of freshwater swamps and bayous in Europe and North America. Mature Orthacanthus reached nearly 3 meters 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 xenacanth sharks and of Orthacanthus.
context_section_description: The teeth of Orthacanthus texensis and Orthacanthus platypternus from bonebeds from the Lower Permian of Texas, and the teeth of Orthacanthus compressus from the Upper Pennsylvanian of Nebraska and Dunkard Basin of the central Appalachians were used to determine the origin of O. texensis and O. platypternus. It has been proposed that both O. texensis and O. platypternus could be derived from O. compressus, where juvenile features of O. compressus are retained in the adult teeth of O. platypternus via paedomorphosis, and the juvenile features of O. compressus teeth are observed in the adult teeth of O. texensis.
  Taxon Mimia sits outside of a clade that contains two monophyletic sister groups. The first monophyletic sister group defines a clade that includes the stem-group chondrichthyans which is visualized as a sister group of Doliodus and a large clade that comprises the cladodont sharks and Orthacanthus. The “cladodont sharks” plus Orthacanthus comprise two monophyletic sister groups: Orthacanthus and the Cladodoides and Tamiobatis on one side, and the Symmoriiformes on the other side. The second monophyletic sister group characterizes crown chondrichthyans which contains two monophyletic sister groups (Euchondrocephali on one side and Euselachii on the other side).
caption: Orthacanthus teeth
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