How are arowanas related to pirarucus and bonytongues?

Arowanas, pirarucus, and bonytongues are all members of the family Osteoglossidae, which belongs to the superorder Osteoglossomorpha, a group widely considered to be among the most primitive bony fishes.123

These fishes share several defining characteristics, most notably the use of their tongue as an opposing surface for teeth when biting food, which is a unique trait among fishes. Within the family Osteoglossidae:2

• Bonytongues: This is a general term often used to describe the entire family, which includes various heavy-bodied tropical freshwater fishes covered in large, hard, mosaic-like scales.13
• Arowanas: These are specific members of the family (primarily in the genera Osteoglossum and Scleropages) known for their laterally compressed bodies and large mouths.14
• Pirarucus: Also known as the arapaima or paiche (*Arapaima gigas*), these are the largest members of the Osteoglossidae family, reaching lengths of up to 2.4 meters.13

While they share a common evolutionary lineage and skeletal structure, they are distinguished by their diverse body forms and geographic distribution across South America, Africa, Asia, and Australia.13