Aspidorhynchiformes (from New Latin "shield-snout forms") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

order 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 hor ...

. It contains only a single family, the Aspidorhynchidae. Members of the group are noted for their elongated, conical rostrums, of varying length, formed from fused

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

e. They are generally interpreted as stem-group teleosts. The range of the group extends from the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

to the late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

Taxonomic history

The order was described by

Pieter Bleeker Pieter Bleeker (10 July 1819 – 24 January 1878) was a Dutch medical doctor, ichthyologist, and herpetologist. He was famous for the ''Atlas Ichthyologique des Indes Orientales Néêrlandaises'', his monumental work on the fishes of East Asia ...

in 1859. Aspidorhynchiformes has one family, which is divided into at least two genera: * Order †Aspidorhynchiformes Bleeker 1859 spidorhynchida; Aspidorhynchoidei Bleeker 1859** Family †Aspidorhynchidae Bleeker 1859 inctiferidae Silva Santos 1990; Diphyodontidae Jordan 1923*** Genus †'' Jonoichthys'' Gouiric-Cavalli 2015 *** Genus ?†'' Ophirachis'' Costa 1854 *** Genus †'' Platycerhynchus'' Costa 1864 *** Genus †'' Pseudovinctifer'' Arratia 2015 *** Genus †'' Richmondichthys'' Bartholomai 2004 *** Genus †''

Aspidorhynchus ''Aspidorhynchus'' (from el, ᾰ̓σπίς 'shield' and el, ῥύγχος 'snout') is an extinct genus of ray-finned fish from the Jurassic and Cretaceous periods. Fossils have been found in Europe and Antarctica. ''Aspidorhynchus'' was a ...

'' Agassiz 1833 non Fitzinger 1843 *** Genus †''

Belonostomus ''Belonostomus'' (from el, βέλος , 'dart' and el, στόμα 'mouth') is a genus of prehistoric ray-finned fish that was described by Louis Agassiz in 1844. It is a member of the order Aspidorhynchiformes, a group of fish known for their ...

'' Agassiz 1834 'Dichelospondylus'' Costa 1856; ''Hemirhynchus">Dichelospondylus.html" ;"title="'Dichelospondylus">'Dichelospondylus'' Costa 1856; ''Hemirhynchus'' Kner 1867 non Agassiz 1844 non Hodgson 1843; ''Diphyodus'' Lambe 1902] *** Genus †''Vinctifer'' Jordan 1920 Fossils range have been found in the United States, France, Italy, Russia, Saskatchewan,

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

, and

Uzbekistan Uzbekistan (, ; uz, Ozbekiston, italic=yes / , ; russian: Узбекистан), officially the Republic of Uzbekistan ( uz, Ozbekiston Respublikasi, italic=yes / ; russian: Республика Узбекистан), is a doubly landlocked cou ...

. These fossils range from 167.7

mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

(''

'') to 66 mya ('' Belonostomus longirostris'').

Anatomy

The most distinctive feature of the Aspidorhynchiformes are the elongated, tube-like rostrums, which are formed from fused premaxillary bones. The scales are lepidosteoid, similar to those of

gar Gars are members of the family Lepisosteidae, which are the only surviving members of the Ginglymodi, an ancient holosteian group of ray-finned fish, which first appeared during the Triassic, over 240 million years ago. Gars comprise seven livin ...

Taxonomy

Aspidorhynchiformes have generally been recovered as basal members of

Teleosteomorpha Neopterygii (from Greek νέος ''neos'' 'new' and πτέρυξ ''pteryx'' 'fin') is a subclass of ray-finned fish (Actinopterygii). Neopterygii includes the Holostei and the Teleostei, of which the latter comprise the vast majority of extant f ...

, more closely related to teleosts than to Holostei. They have often considered to have a

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

relationship with

Pachycormiformes Pachycormiformes is an extinct order of marine ray-finned fish known from the Early Jurassic to the end of the Cretaceous. It only includes a single family, Pachycormidae. They were characterized by having serrated pectoral fins (though more rece ...

, another group of basal teleosteomorphs.

Evolutionary history

The earliest known remains of the group are known from the Middle Jurassic of Europe, in what was then the western Tethys Ocean, which was likely the centre of their initial diversification, during the Late Jurassic they dispersed to the waters around the Caribbean, South America and Antarctica. During the Cretaceous they dispersed worldwide. The youngest members the group, belonging to ''

'' went extinct during the late

References

paleodb
Prehistoric ray-finned fish orders {{paleo-rayfinned-fish-stub