Hybodont

Ecology

Hybodont fossils are found in depositional environments ranging from marine to fluvial (river deposits). Many hybodonts are thought to have been euryhaline, able to tolerate a wide range of salinities. Hybodonts inhabited freshwater environments from early in their evolutionary history, spanning from the Carboniferous onwards. Based on isotopic analysis, some species of hybodonts are likely to have permanently lived in freshwater environments, while others may have migrated between marine and freshwater environments. One genus of hybodont, Onychoselache of the lower Carboniferous of Scotland, is suggested to have been capable of amphibious locomotion, similar to modern orectolobiform sharks such as bamboo and epaulette sharks, due to its well-developed pectoral fins. It has been suggested that male hybodonts used their cephalic spines to grip females during mating. Preserved egg cases of hybodonts assigned to Palaeoxyris indicate that at least some hybodonts laid their eggs in freshwater and brackish environments, with the eggs being attached to vegetation via a tendril. Laying of eggs in freshwater is not known in any living cartilaginous fish. At least some hybodonts are suggested to have utlilized specific sites as nurseries, such as in the Triassic lake deposits of the Madygen Formation of Kyrgyzstan, where eggs of Lonchidion are suggested to have been laid on the lakeshore or upriver areas, where the juveniles hatched and matured, before migrating deeper into the lake as adults.