to female, is much less common than protogyny. Most families use external rather than internal fertilization. Of the oviparous teleosts, most (79%) do not provide parental care. Viviparity, ovoviviparity, or some form of parental care for eggs, whether by the male, the female, or both parents is seen in a significant fraction (21%) of the 422 teleost families; no care is likely the ancestral condition. The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of Saurichthys. Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care. Male territoriality "preadapts" a species for evolving male parental care. There are a few examples of fish that self-fertilise. The mangrove rivulus is an amphibious, simultaneous hermaphrodite, producing both eggs and spawn and having internal fertilisation. This mode of reproduction may be related to the fish's habit of spending long periods out of water in the mangrove forests it inhabits. Males are occasionally produced at temperatures below and can fertilise eggs that are then spawned by the female. This maintains genetic variability in a species that is otherwise highly inbred. Classification and fossil record Actinopterygii is divided into the classes Cladistia and Actinopteri. The latter comprises the subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, is divided into the infraclasses Holostei and Teleostei. During the Mesozoic (Triassic, Jurassic, Cretaceous) and Cenozoic the teleosts in particular diversified widely. As a result, 96% of living fish species are teleosts (40% of all fish species belong to the teleost subgroup Acanthomorpha), while all other groups of actinopterygians represent depauperate lineages. The classification of ray-finned fishes can be summarized as follows: Cladistia, which include bichirs and reedfish Actinopteri, which include: Chondrostei, which include Acipenseriformes (paddlefishes and sturgeons) Neopterygii, which include: Teleostei (most living fishes) Holostei, which include: Lepisosteiformes (gars) Amiiformes (bowfin) The cladogram below shows the main clades of living actinopterygians and their evolutionary relationships to other extant groups of fishes and the four-limbed vertebrates (tetrapods). The latter include mostly terrestrial species but also groups that became secondarily aquatic (e.g. Whales and Dolphins). Tetrapods evolved from a group of bony fish during the Devonian period. Approximate divergence dates for the different actinopterygian clades (in millions of years, mya) are from Near et al., 2012. The polypterids (bichirs and reedfish) are the sister lineage of all other actinopterygians, the Acipenseriformes (sturgeons