Osteoglossiformes

Osteoglossiformes is an order of ray-finned fishes known commonly as bonytongues. They are among the most primitive living teleosts, with a fossil record extending back to the Early Cretaceous. The group is distributed primarily in tropical freshwater systems of Africa, South America, and Asia, with some representatives in Australia.

Characteristic features include a toothed, bony palatal apparatus that gave the group its common name, and a variety of body forms ranging from medium to very large. Most species inhabit rivers, floodplains, and lakes, where they can be strong, sometimes predatory swimmers. Several taxa have adaptations for air-breathing or gas exchange at the surface, enabling survival in low-oxygen waters.

Taxonomy of Osteoglossiformes comprises multiple families, including Osteoglossidae (bonytongues, with genera Osteoglossum and Scleropages, the latter including several Asian and Australian arowana species), Notopteridae (featherbacks, genus Notopterus and allies), Pantodontidae (Pantodon buchholzi, the African butterflyfish), Hiodontidae (mooneyes, genus Hiodon), Arapaimidae (arapaima), and Heterotidae (African bonytongue, Heterotis).

Ecology and human use: pirarucu (Arapaima gigas) is among the world's largest freshwater fishes and is important in Amazonia for food; Asian arownas are valued in the ornamental fish trade. Many Osteoglossiformes species are threatened by overfishing, habitat loss, and pollution, and some trade is regulated under international agreements.

Conservation status varies by species; some are assessed by IUCN and subject to regional protections. The order remains of interest to evolutionary biology because of its ancient lineage among teleosts.