Aspidorhynchiformes (from

New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...

"shield-snout forms") is an extinct 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 h ...

. 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 ...

e. They are generally interpreted as

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

s. The range of the group extends from the Middle Jurassic to the late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

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'' Agassiz 1833 non Fitzinger 1843 *** Genus †'' Belonostomus'' Agassiz 1834 'Dichelospondylus''_Costa_1856;_''Hemirhynchus.html" ;"title="Dichelospondylus.html" ;"title="'Dichelospondylus">'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 indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, So ...

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 Columb ...

Wyoming Wyoming () is a state in the 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 southwest, and Colorado to the s ...

, 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 co ...

. These fossils range from 167.7 mya ('' Aspidorhynchus'') to 66 mya (''

Belonostomus longirostris ''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 ...

'').

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 Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Teleo ...

than to

Holostei 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 ...

. They have often considered to have a sister group 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 The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

, 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 '' Belonostomus'' went extinct during the late

References

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