Evolution and systematics

The fossil record of the Stromateoidei is not very extensive, consisting mostly of isolated otoliths, the paired ear-stones present in the membranous labyrinth of the inner ear of many fishes that can aid in detecting motion. Otoliths are difficult to identify because they usually lack the diagnostic features of families of fishes. Irrespective of this, the earliest otoliths attributed to a stromateoid date from the early Tertiary period (about 50 million years ago), of France, Belgium, and England. Fossils known from more than otoliths, such as skeletons, are rare, and these are also fragmentary, such as Psenicubiceps alatus from Russia, currently assigned to the stro-mateoid family Nomeidae. The earliest stromateoid fossils are believed to be from Denmark, from deposits as old as 60 million years, but these cannot presently be assigned with confidence to the Stromateoidei.

The Stromateoidei is a suborder of the large bony fish order Perciformes. The composition of this suborder has changed only slightly in the past 35 years; it was mostly assembled in a landmark study in 1966 by Humphry Greenwood, Donn E. Rosen, Stanley H. Weitzman, and George S. Myers, in which all families were grouped together except the Amarsipidae, which was added in 1969. The Stromateoidei currently includes 6 families, 15 genera, and some 65 species. The families are: Amarsipidae (with a single genus and species, Amarsipus carlsbergi), Nomeidae (driftfishes; 3 genera and 15 species), Centrolophidae (medusafishes; 7 genera and 27 species), Tetragonuridae (squaretails; 1 genus, Tetragonurus, and 3 species), Stromateidae (butterfishes; 3 genera and 13 species), and Ariommatidae (1 genus, Ariomma, and 6 species).

Within the Perciformes, stromateoids are more closely related to certain generalized families that share a specific arrangement of the ramus lateralis accessorius (a facial nerve complex), including the Kyphosidae, Girellidae, Scorpididae, Arripididae, Kuhliidae, Microcanthidae, Oplegnathidae, and Terapontidae. Of these families, the stromateoids are more closely related to the Kyphosidae (chubs), sharing with them details of their tooth pattern and larval pigmentation. Evolutionary relationships within the Stromateoidei indicate that the Amarsipidae are the most basal group, that the Centrolophidae may not have unique features, and that the butterfishes (Stromateidae) are the most derived stromateoids.

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