Notes about Terminal Taxa
The Gonorynchiformes includes two modern Indo-Pacific species (Chanos chanos, Gonorynchus gonorynchus) placed in monotypic families. Several fossils are assigned to the Chanidae and Gonorynchidae (Patterson, 1975, 1987), the oldest of which are early Cretaceous. There are 24 extant gonorynchiform species in the African freshwater family Kneriidae.
Characins, catfishes, electric (knife) fishes, carps and loaches comprise a well-known higher teleostean lineage named Otophysi (Ostariophysi in older literature). This clade accounts for over 25% of modern fish species (Nelson, 1994), and most of these live exclusively in freshwater.
Evolution and Systematics
Discussion of Phylogenetic Relationships
Otophysan monophyly is supported by several synapomorphies of which the best known are auditory specializations of the inner ear, anterior vertebrae (the Weberian complex), and gas bladder. Greenwood et al. (1966) and Rosen and Greenwood (1970) found related modifications of the gas bladder and other structures in the Gonorynchiformes. Rosen and Greenwood (1970) united the gonorynchiforms with characins, catfishes, cypriniforms and knife fishes into Ostariophysi, and coined the new name Otophysi for the more traditional assemblage (i.e. less gonorynchiforms). The hypothesis of sister taxon relationship between the Gonorynchiformes and Otophysi has held up under subsequent study.
In 1981 Fink and Fink published a cladistic study of the Otophysi that significantly departed from traditional concepts of interrelationships. A clade uniting Gymnotiformes plus Siluriformes was proposed to be the sister lineage of Characiforms, and these three are the sister taxon of the Cypriniformes.