The two suborders that comprise this chapter, the flat-heads (Platycephaloidei) and flying gurnards (Dactylopteroidei) are mail-cheeked fishes (order Scorpaeniformes). This old group (first recognized in 1829), composed of approximately 1,400 species, is united by the presence of the suborbital stay. The suborbital stay is a bony strut that connects the bones under the eye with the front of the gill cover. Some authors have suggested that the suborbital stay in the flying gurnards evolved independently from the remainder of the scorpaeni-form fishes. These authors place the flying gurnards in their own order (Dactylopteriformes).
In 1758 the father of binomial nomenclature, Carl Linnaeus, was the first naturalist to describe species of both the flying gurnards and the flatheads. Since the time of Linnaeus, six additional flying gurnards and 86 additional platycephaloids have been described. The seven flying gurnards are now classified into two genera (Dactylopterus in the Atlantic and Dactyloptena in the Indo-Pacific). The 88 platycephaloids have been classified variously into three to seven families, depending on the researcher. For the purposes of this review, the Platycephaloidei are split into three families: the flatheads (Platy-cephalidae, 64 species), the ghost flatheads (Hoplichthyidae, 11 species), and the deepwater flatheads (Bembridae, 11 species). At this time, there is considerable debate about the placement and classification of both of these suborders, so the classification follows Joseph Nelson's 1994 book, Fishes of the World.
Traditionally, the flying gurnards have been allied with the sea robins (Triglidae and Peristediidae), because both groups share enlarged pectoral fins and free pectoral rays, which these fishes use like legs to "walk" on the seafloor. Recently, researchers have suggested that the suborbital stay in flying gurnards evolved independently of the strut found in other mail-cheeked fishes. These ichthyologists have suggested that flying gurnards are related to the seahorses and their relatives (Sygnathoidei) or to the tilefishes (Malacanthidae). Because of these different views, the interrelationships of the flying gurnards remain unclear, and they are treated here as scor-paeniforms, pending resolution of their placement.
The placement of the flatheads and their relatives is not clear either. Historically, the three flathead families have been united because of their elongate bodies and depressed or "flattened" heads; hence their common name. Recent work by Hi-sashi Imamura has suggested that the sea robins and their relatives (Triglidae and Peristediidae) may have evolved from a flathead relative, suggesting that the sea robins should be placed in the Platycephaloidei. Clearly, further work using both morphological and DNA sequence data will shed light on the interrelationships and intrarelationships of the flat-heads and their allies.
At more than 50 million years old, the enigmatic Pterygo-cephalus paradoxus from the Monte Bolca formation in Italy may be the oldest known flying gurnard, but the fossil Pre-volitans faedoensis from Eocene deposits in northern Italy is the oldest clearly identifiable flying gurnard. Flatheads first appear in the fossil record with an Eocene otolith (ear stone) record identified as Platycephalusjaneti from France. Whole fossilized skeletal specimens of Platycephalus date to the early Miocene in Tasmania.
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