Redfieldiid
Redfieldiiformes
Extinct order of ray-finned fishes
Redfieldiiformes is an extinct order of ray-finned fish (actinopterygians) which lived from the Middle Triassic to Early Jurassic. Redfieldiiforms were fairly typical Triassic fish in overall anatomy. They had a fusiform (streamlined, tuna-like) body shape with thick, ganoine-covered scales. The dorsal and anal fins were large, positioned opposite from each other, and shifted back, close to the tail. The caudal fin was hemiheterocercal, with the vertebral column and body scales extending into an upper lobe equal in size and shape to the lower lobe. They also had several characteristic skeletal traits, such as a hatchet-shaped preopercle, a series of fulcra (thin spiny scales) fringing the fins, a reduced number of branchiostegal rays (typically just one), and a snout ornamented with tubercles.[1][2][3]
The maxilla has small teeth and is strongly connected to the preopercle; this would have allowed a deep gape to assist in ram feeding.[1] The function of the snout tubercles is uncertain; some authors have suggested that they attached to a fleshy upper lip,[2] while others argue that they could have held sensory organs akin to the tubercles of siluriforms (catfish).[3]
Redfieldiiforms were fairly primitive 'subholostean' fish (more primitive than holosteans such as gars or the bowfin), with uncertain relations to neopterygians.[1] Some studies draw comparisons to 'perleidiforms' or ptycholepids, while others consider redfieldiiforms to be early neopterygians related to pholidopleuriforms.[4] Redfieldiiforms were exclusively freshwater fish which became prominent in southern Gondwana (Argentina, Australia, southern Africa) during the Middle Triassic.[3] By the Late Triassic they had become a major component of freshwater ecosystems in western Laurasia (North America and Morocco). However, they were much rarer further east (South Korea,[3] possibly Switzerland[5]). The last member of the order, Redfieldius, lived in the Early Jurassic of eastern North America.[1][3]
.jpg){kind=link}