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Actinopterygian node A (node defining basal-most ACTINOPTERYGII):T-shaped dermosphenotic contacting nasal, no postorbital or squamosal, enclosed mandibular canal in dentary, one or two pairs of extrascapulars, single dorsal fin, ganoin in scales and dermal bones, rhomboidal scales articulated with peg-and-socket.
The Cheirolepididae is the oldest clade known belonging to the Actinopterygii. These fish are typically small, slender and long, with strongly heterocercal tails, although the ray-supported fin beneath it makes it appear nearly symmetrical. The dorsal and anal fins are large and triangular, paired pectoral and pelvic fins are also present. Small rhomboidal scales cover the body arranged in rows running backwards and downwards, and articulate between themselves through a peg and socket arrangement. Ridge scales act as cutwaters on the dorsal edge of the tail. Fin rays are covered and stiffened by jointed dermal bones. Scales are composed of three main layers of hard tissues: bone, dentine and ganoin (similar to enamel) from the inside out.
Cheirolepidids' skulls are kinetic (various cranial bones move relative to each other, enabling extremely wide gapes), but heavy - with thick bony plates forming the braincase and palatal elements. Maxilla, premaxilla, dentaries and palatal bones possess teeth. Their eyes were large, and they possessed two pairs of nostrils.
Presumably, Cheirolepis was a predatory fish, hunting prey up to two thirds its own size (according to the large gape of its mouth), although its swimming capacities probably made it clumsy for sharp turns.
Such Devonian Actinopterygians are known worldwide, but only ten genera have been discovered so far.