Protacanthopterygii
Encyclopedia
Protacanthopterygii is a ray-finned fish taxon
ranked as a superorder of the infraclass Teleostei
. They inhabit both marine
and freshwater
habitat
. They appear to have evolved in the Cretaceous
or perhaps late Jurassic
, originating probably roughly 150 million years ago; fossil
s of them and the closely related Otocephala are known from throughout the Cretaceous.
and other traits commonly found in this superorder are: more than 24 vertebrae, epicentral cartilage
s, one supraorbital
bone, and a mesocoracoid
, an adipose fin and (often prominent) glossohyal
teeth. However, they usually lack a protrusible upper jaw
, a gular
plate and proximal forking of the intermuscular bones. Most members of this family are rather specialization
mid-sized to larger predators of smaller animals.
As a group, they prefer temperate
waters and are far more diverse in the Northern Hemisphere
than in the Southern
. Some are anadromous migrants
and many are quite euryhaline
. Thus, it is likely that they originated in nearshore or brackish waters of the N hemisphere – theoretically the original protacanthopterygian might have been a catadromous migrant inhabiting freshwater, but given that the basal Otocephala were very likely marine this seems not so likely. Given that they are widespread in the Holarctic
but reached the Southern hemisphere in the Pacific region, it is more likely than not that they originated in general region of the Turgai Strait and the nearby Tethys Sea – perhaps towards the Eastern Tethys as they never seem to have settled Africa or Atlantic South America
.
, catfish
and herring
s in superorders Clupeomorpha and Ostariophysi
. While the core of the present superorder has always consisted of three orders, additional taxa are likely to belong here but are more disputed.
In recent times, there is a trend to split
the Osmeriformes
in two, as their supposed suborders do not seem to be particularly closely related among the Protacanthopterygii. The resultant order Argentiniformes
contains a number of peculiar deep sea
forms. And as it seems, the superorders Cyclosquamata and Stenopterygii
which contain some bizarre apomorphic forms are so closely related to the "traditional" Protacanthopterygii as to be included therein. Alternatively, the unranked clade
name Euteleostei has been proposed for the whole group, but that would require splitting up the Protacanthopterygii lest they become paraphyletic. Thus, up to seven orders might be included here:
Protacanthopterygii sensu stricto
"Stenopterygii"
"Cyclosquamata"
The placement of the Myctophiformes
, traditionally held to be close relatives of the Aulopiformes
and separated in a superorder "Scopelomorpha", as well as the Lampriformes
(the monotypic superorder Lampridiomorpha, and putative relatives of the "Stenopterygii") consequently warrants further study. However, these two seem to be somewhat more advanced and closer to the Paracanthopterygii
.
More dubiously, the Cetomimiformes
and "Ctenothrissiformes" are sometimes placed here. While they are indeed of uncertain relationships, the former are widely assumed to belong to superorder Acanthopterygii
and be closely related to the Stephanoberyciformes
. Thus, it is rather unlikely that they are correctly placed here. As regards the latter, it is an entirely fossil
group and may well be an invalid paraphyletic assemblage of ancient Teleostei
, and in part may indeed belong in the Protacanthopterygii sensu lato.
The supposed family "Macristiidae" was sometimes considered the only extant member of the "Ctenothrissiformes". But actually these are larva
e of certain Aulopiformes, as was already suspected when the first "macristiid" was scientifically studied. They were subsequently split as a distinct family and placed in the Osmeriformes. This is interesting in the light of the modern view that these two orders are not nearly as distantly related as they were believed throughout most of the 20th century.
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
ranked as a superorder of the infraclass Teleostei
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
. They inhabit both marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
. They appear to have evolved in the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
or perhaps late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, originating probably roughly 150 million years ago; fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of them and the closely related Otocephala are known from throughout the Cretaceous.
Characteristics and origin
Protacanthopterygii contains a number of moderately advanced teleosts. AnatomicalFish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
and other traits commonly found in this superorder are: more than 24 vertebrae, epicentral cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
s, one supraorbital
Supraorbital
Supraorbital refers to the region immediately above the eye sockets, where in humans the eyebrows are located. It denotes several anatomical features, such as:*Supraorbital artery*Supraorbital foramen*Supraorbital gland*Supraorbital nerve...
bone, and a mesocoracoid
Mesocoracoid
Mesocoracoid is a bone of the pectoral girdle....
, an adipose fin and (often prominent) glossohyal
Glossohyal
Glossohyal is the term used in fish anatomy for the tongue and hyoid bone. It is the lingual plate, which is a dermal toothed bone that covers or fuses with the basihyal. The glossohyal changes its proportions when the fish increases in size....
teeth. However, they usually lack a protrusible upper jaw
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
, a gular
Gular
Gular is of or pertaining to the throat, and may more specifically refer to:* Gular scales in reptiles* Gular scute, or gular projection, in turtles and tortoises* Gular fold in lizards...
plate and proximal forking of the intermuscular bones. Most members of this family are rather specialization
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
mid-sized to larger predators of smaller animals.
As a group, they prefer temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
waters and are far more diverse in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
than in the Southern
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. Some are anadromous migrants
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
and many are quite euryhaline
Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
. Thus, it is likely that they originated in nearshore or brackish waters of the N hemisphere – theoretically the original protacanthopterygian might have been a catadromous migrant inhabiting freshwater, but given that the basal Otocephala were very likely marine this seems not so likely. Given that they are widespread in the Holarctic
Holarctic
The Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...
but reached the Southern hemisphere in the Pacific region, it is more likely than not that they originated in general region of the Turgai Strait and the nearby Tethys Sea – perhaps towards the Eastern Tethys as they never seem to have settled Africa or Atlantic South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
Systematics
As mentioned initially, one of the closest relatives of the Protacanthopterygii are the Otocephala, which include such different fishes as carpCarp
Carp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain...
, catfish
Catfish
Catfishes 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 heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
and herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
s in superorders Clupeomorpha and Ostariophysi
Ostariophysi
Ostariophysi is the second-largest superorder of fish. Members of this superorder are called ostariophysians. This diverse group contains almost 8,000 species, about 28% of known fish species in the world and 68% of freshwater species, and are present on all major continents except Antarctica...
. While the core of the present superorder has always consisted of three orders, additional taxa are likely to belong here but are more disputed.
In recent times, there is a trend to split
Lumpers and splitters
Lumping and splitting refers to a well-known problem in any discipline which has to place individual examples into rigorously defined categories. The lumper/splitter problem occurs when there is the need to create classifications and assign examples to them, for example schools of literature,...
the Osmeriformes
Osmeriformes
Osmeriformes is an order of ray-finned fish that includes the true or freshwater smelts and allies, such as the galaxiids and noodlefishes; they are also collectively called osmeriforms. They belong to the teleost superorder Protacanthopterygii, which also includes pike and salmon, among others...
in two, as their supposed suborders do not seem to be particularly closely related among the Protacanthopterygii. The resultant order Argentiniformes
Argentiniformes
Argentiniformes is an order of ray-finned fish whose distinctness was recognized only fairly recently. In former times, they were included in the Osmeriformes as suborder Argentinoidei. That term refers only to the suborder of marine smelts and barreleyes in the classification used here, with the...
contains a number of peculiar deep sea
Deep sea
The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...
forms. And as it seems, the superorders Cyclosquamata and Stenopterygii
Stenopterygii
Stenopterygii are a superorder of ray-finned fish in the infraclass Teleostei. Their validity is somewhat doubtful, as the group was established to separate, out of a large group of closely related Teleostei, a mere two rather peculiarly autapomorphic orders at best...
which contain some bizarre apomorphic forms are so closely related to the "traditional" Protacanthopterygii as to be included therein. Alternatively, the unranked clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
name Euteleostei has been proposed for the whole group, but that would require splitting up the Protacanthopterygii lest they become paraphyletic. Thus, up to seven orders might be included here:
Protacanthopterygii sensu stricto
- ArgentiniformesArgentiniformesArgentiniformes is an order of ray-finned fish whose distinctness was recognized only fairly recently. In former times, they were included in the Osmeriformes as suborder Argentinoidei. That term refers only to the suborder of marine smelts and barreleyes in the classification used here, with the...
– barreleyes, slickheads and allies - EsociformesEsociformesEsociformes is a small order of ray-finned fish, with two families, the Umbridae and the Esocidae . The pikes of genus Esox give the order its name. There are ten species — five in each family....
– pikes and mudminnows - OsmeriformesOsmeriformesOsmeriformes is an order of ray-finned fish that includes the true or freshwater smelts and allies, such as the galaxiids and noodlefishes; they are also collectively called osmeriforms. They belong to the teleost superorder Protacanthopterygii, which also includes pike and salmon, among others...
– galaxiids, true smelts and allies - Salmoniformes – salmons, trouts and allies
"Stenopterygii"
- Ateleopodiformes – jellynose fishes
- StomiiformesStomiiformesStomiiformes is an order of deep-sea ray-finned fishes of very diverse morphology. It includes for example dragonfishes, lightfishes, loosejaws, marine hatchetfishes and viperfishes. The order contains 4 families with more than 50 genera and almost 400 species...
– dragonfishes, marine hatchetfishes and allies
"Cyclosquamata"
- AulopiformesAulopiformesAulopiformes is an order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies or aulopiforms are sometimes used for this group...
– lancetfishes, lizardfishes and alies
The placement of the Myctophiformes
Myctophiformes
Myctophiformes is an order of ray-finned fish consisting of two families of deep-sea marine fish, most notably the highly abundant lanternfishes...
, traditionally held to be close relatives of the Aulopiformes
Aulopiformes
Aulopiformes is an order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies or aulopiforms are sometimes used for this group...
and separated in a superorder "Scopelomorpha", as well as the Lampriformes
Lampriformes
Lampriformes is an order of ray-finned fish. They are collectively called "lamprids" or lampriforms, and unite such open-ocean and partially deep-sea Teleostei as the crestfishes, oarfish, opahs and ribbonfishes...
(the monotypic superorder Lampridiomorpha, and putative relatives of the "Stenopterygii") consequently warrants further study. However, these two seem to be somewhat more advanced and closer to the Paracanthopterygii
Paracanthopterygii
Paracanthopterygii is a superorder of fishes. Members of this superorder are called paracanthopterygians.It includes five orders:* Percopsiformes * Batrachoidiformes * Lophiiformes...
.
More dubiously, the Cetomimiformes
Cetomimiformes
The Cetomimiformes or whalefishes are an order of small, deep-sea ray-finned fish. Some authorities include the whalefishes as part of the order Stephanoberyciformes, within the superfamily Cetomimoidea. Their sister order, the Beryciformes, includes the flashlight fish and squirrelfish.Within this...
and "Ctenothrissiformes" are sometimes placed here. While they are indeed of uncertain relationships, the former are widely assumed to belong to superorder Acanthopterygii
Acanthopterygii
Acanthopterygii is a superorder of bony fishes in the class Actinopterygii. Members of this superorder are also known as the ray-finned fishes for the characteristic sharp, bony rays in their fins; however this name is also often given to the class Actinopterygii as a whole.Orders:* Order...
and be closely related to the Stephanoberyciformes
Stephanoberyciformes
The Stephanoberyciformes are an order of marine ray-finned fishes, consisting of about 45 species, the majority of which belong to the ridgehead family . The Stephanoberyciformes are mostly uncommon deep-sea species with little, if any, importance to commercial fishery...
. Thus, it is rather unlikely that they are correctly placed here. As regards the latter, it is an entirely fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
group and may well be an invalid paraphyletic assemblage of ancient Teleostei
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
, and in part may indeed belong in the Protacanthopterygii sensu lato.
The supposed family "Macristiidae" was sometimes considered the only extant member of the "Ctenothrissiformes". But actually these are larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of certain Aulopiformes, as was already suspected when the first "macristiid" was scientifically studied. They were subsequently split as a distinct family and placed in the Osmeriformes. This is interesting in the light of the modern view that these two orders are not nearly as distantly related as they were believed throughout most of the 20th century.