Redfieldiiformes is an extinct

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

(actinopterygians) which lived from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma ...

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma ...

. Redfieldiiforms were fairly typical Triassic fish in overall anatomy. They had a

fusiform Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon-shape, but often implies a focal broadening of a structure that continues from one or both ends, such as an aneurysm on a ...

(streamlined,

tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max le ...

-like) body shape with thick,

ganoine Ganoine or ''ganoin'' is a glassy, often multi-layered mineralized tissue that covers the scales, cranial bones and fin rays in some non-teleost ray-finned fishes, such as gars, bichirs, and coelacanths. It is composed of rod-like, pseudopris ...

-covered scales. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

and

anal Anal may refer to: Related to the anus *Related to the anus of animals: ** Anal fin, in fish anatomy ** Anal vein, in insect anatomy ** Anal scale, in reptile anatomy *Related to the human anus: ** Anal sex, a type of sexual activity involving ...

fins were large, positioned opposite from each other, and shifted back, close to the tail. The

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

was hemiheterocercal, with the vertebral column and body scales extending into an upper lobe which was equal in size and shape to the lower lobe. They also had several characteristic skeletal traits, such as a hatchet-shaped

preopercle The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bo ...

, a series of fulcra (thin spiny scales) fringing the fins, a reduced number of

branchiostegal rays This glossary of ichthyology is a list of definitions of terms and concepts used in ichthyology, the study of fishes. A B C ...

(typically just one), and a snout ornamented with tubercles. The

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

has small teeth and is strongly connected to the preopercle; this would have allowed a deep gape to assist in

ram feeding Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifi ...

. The function of the snout tubercles is uncertain; some authors have suggested that they attached to a fleshy upper lip, while others argue that they could have held sensory organs akin to the tubercles of siluriforms (

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

). Redfieldiiforms were fairly primitive 'subholostean' fish (more primitive than

holosteans Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by a single living species, the bowfin ('' Amia calva''), as well as the Ginglymodi, the sole living representatives being the gars ( ...

such as gars or the

bowfin The bowfin (''Amia calva'') is a bony fish, native to North America. Common names include mudfish, mud pike, dogfish, grindle, grinnel, swamp trout, and choupique. It is regarded as a relict, being the sole surviving species of the Halecomorp ...

), with uncertain relations to neopterygians. Some studies draw comparisons to ' perleidiforms' or ptycholepids, while others consider redfieldiiforms to be early neopterygians related to pholidopleuriforms. Redfieldiiforms were exclusively freshwater fish which became prominent in southern

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

(

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

, Australia, southern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

) during the Middle Triassic. By the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

they had become a major component of freshwater ecosystems in western

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

( North America and

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria ...

), though they were much rarer further east (

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...

, possibly Switzerland). The last member of the order, '' Redfieldius'', lived in the Early Jurassic of eastern North America.

Genera

* ''

Atopocephala ''Atopocephala'' is an extinct genus of prehistoric freshwater ray-finned fish that lived during the Middle Triassic epoch. It contains a single species, ''A. watsoni'' from the Karoo Supergroup of South Africa. A potential indeterminate specie ...

'' * ''

Brookvalia ''Brookvalia'' is an extinct genus of prehistoric bony fish that lived during the Early Triassic epoch. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to: ...

'' * '' Calaichthys'' * '' Cionichthys'' * ''

Daedalichthys ''Daedalichthys'' is an extinct genus of prehistoric freshwater ray-finned fish that lived during the Early Triassic epoch. It contains a single species, ''D. formosa'' (=''D. higginsi'' Warren, 1936) from the Olenekian-aged ''Cynognathus'' As ...

'' * '' Denwoodichthys?'' * ''

Dictyopyge ''Dictyopyge'' is an extinct genus of prehistoric bony fish that lived during the Late Triassic epoch.Olsen, P. E., McCune, A. R. & Thomson, K. S. (1982). Correlation of the Early Mesozoic Newark Supergroup by vertebrates, principally fishes. Ame ...

'' * '' Endemichthys?'' * '' Geitonichthys'' * '' Helichthys'' * '' Hiascoactinus'' * ''

Ischnolepis ''Ischnolepis'' is a species of plants in the family Apocynaceae first described as a genus in 1909. It contains only one known recognized species, ''Ischnolepis graminifolia'', endemic to Madagascar Madagascar (; mg, Madagasikara, ), of ...

'' * '' Lasalichthys'' * '' Leighiscus?'' * '' Mauritanichthys'' * '' Molybdichthys'' * '' Pacorichthys?'' * '' Phlyctaenichthys'' * '' Redfieldius'' * ''

Sakamenichthys ''Sakamenichthys'' is an extinct genus of prehistoric bony fish that lived during the Early Triassic epoch. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to ...

?'' * '' Schizurichthys'' * '' Sinkiangichthys (

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

)?'' * '' Synorichthys''

References

Prehistoric ray-finned fish orders {{Triassic-fish-stub