These are closely related to the Salmoniformes, the two comprising the superorder Protacanthopterygii, and are often included in their order. The esociform fishes first appeared in the mid-Cretaceous -- early products of the Euteleost radiation of that time. Today they are found only in fresh water in North America and Europe.
Most esociforms are classic ambush predators, with long well-muscled torsos, the dorsal and anal fins set well back and opposite each other for rapid acceleration along a straight line. Anatomically, they are characterized by a number of features, including a toothless maxilla, absence of an adipose fin; and the absence of breeding tubercules.