Euryhaline adaptation was not confirmed in the 2013 analysis. Predator-Prey relationship Orthacanthus and Triodus have a predator-prey relationship where specifically there is predation of Orthacanthus on Triodus. Cranial remains of specimens of both Orthacanthus and Triodus were from the Upper Carboniferous in Puertollano basin, Spain, and give evidence of this predator-prey relationship. Numerous and well preserved cephalic elements of Triodus were associated with the cranial remains of Orthacanthus, and is explained by the inclusion of occipital spines of Triodus in the buccal cavity of Orthacanthus. Additional evidence is the co-occurrence of one Orthacanthus spine with many Triodus spines, which likely penetrated the soft tissue and cartilage of the mouth of Orthacanthus, similarly to modern sharks that feed on stingrays where the spines of stingrays have been found within and around the buccal cavities of Carcharhinus, Galeocerdo, Negaprion and Sphyrna. Examination of Orthacanthus coprolites from Canada by Aodhan O' Gogain et al. revealed that in times of hardship, Orthacanthus was likely cannibalistic, as teeth from juvenile Orthacanthus were found within the coprolites of adults. Orthacanthus had a catholic diet that consisted of actinopterygians, acanthodians, dipnoans, xenacanthids and tetrapods, based on analysis of coprolites and gut contents. There have also been suspicions of filial cannibalism due to the presence of juvenile Orthacanthus teeth inside an Orthacanthus coprolite. The poop of Orthacanthus has a unique spiraling shape due to a corkscrew-shaped rectum. Paleoecology The palaeobiogeographical distribution of O. platypternus suggests ontogenetic habitat partitioning. Ontogenetic niche theory predicts that individuals may change their habitat or diet to maintain optimal growth rates or to improve trade-offs between mortality risk and growth. While smaller individuals likely lived in shallower waters such as in small ponds and stream channels of the coastal plain, larger individuals likely lived in deeper water such as the fluvio-lacustrine (rivers and lakes) and marginal marine areas. The oldest known specimen of Orthacanthus, Diplodus problematicus was found in New Brunswick, Canada, from the Emsian, ranging between 407 and 393 million years ago. Other specimens have been found in locations including the US, the United Kingdom, Poland, and France. References Carboniferous sharks Permian sharks Paleozoic animals of Europe Prehistoric cartilaginous fish genera Paleozoic animals of North America Fossil taxa described in 1843