Hybodonts share a close common ancestry with modern sharks and rays (Neoselachii) as part of the clade Euselachii.

[2] Hybodontiformes are total group-elasmobranchs and the sister group to Neoselachii, which includes modern sharks and rays.

Due to their cartilaginous skeletons usually disintegrating upon death like other chondrichthyans, hybodonts are generally described and identified based on teeth and fin spine fossils, which are more likely to be preserved.

Hybodont teeth served a variety of functions depending on the species, including grinding, crushing (durophagy), tearing, clutching, and even cutting.

[12] Similar fin spines are also found in many extinct chondrichthyan groups as well as in some modern sharks like Heterodontus and squalids.

[21] Hybodonts inhabited freshwater environments from early in their evolutionary history, spanning from the Carboniferous onwards.

[28][19][29] 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.

[30] Some hybodonts like Hybodus are thought to have been active predators capable of feeding on swiftly moving prey,[2] with preserved stomach contents of a specimen of Hybodus hauffianus indicating that they fed on belemnites (a type of extinct squid-like cephalopod).

During the Triassic and Early Jurassic, hybodontiforms were the dominant elasmobranchs in both marine and non-marine environments.

[20] As neoselachians (group of modern sharks) diversified further during the Late Jurassic, hybodontiforms became less prevalent in open marine conditions but remained diverse in fluvial and restricted settings during the Cretaceous.

[20] Possible reasons for the replacement of hybodonts by modern sharks include more effective locomotory and jaw movement mechanisms of the latter group.

[37] By the end of the Cretaceous, hybodonts had declined to only a handful of species,[38] including members of Lonchidion[39], and Meristodonoides.

[40] The last hybodonts disappeared, seemingly abruptly, as part of the Cretaceous-Paleogene extinction event approximately 66 million years ago.