''Eusthenopteron'' (from 'stout', and 'wing' or 'fin') is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

prehistoric Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

marine

lobe-finned fish Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

known from several

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

that lived during the Late

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

period, about 385 million years ago. It has attained an iconic status from its close relationship to

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s. Early depictions of animals of this genus show them emerging onto land, but paleontologists now think that ''Eusthenopteron'' species were strictly aquatic

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s, though this is not completely known.M. Laurin, F. J. Meunier, D. Germain, and M. Lemoine 2007
A microanatomical and histological study of the paired fin skeleton of the Devonian sarcopterygian ''Eusthenopteron foordi''
''Journal of Paleontology'' 81: 143–153. The genus was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha,

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. Some 2,000 ''Eusthenopteron'' specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers by paleoichthyologist Erik Jarvik between the 1940s and the 1990s. Further species have been described from other parts of Canada and northern Europe, indicating that this genus had a wide distribution.

Taxonomy

''Eusthenopteron'' is placed in the family

Tristichopteridae Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged ...

, which has also been alternatively named Eusthenopteridae after this genus. It is related to genera such as ''

Tristichopterus ''Tristichopterus'', with a maximum length of sixty centimetres, is the smallest genus in the family of prehistoric lobe-finned fish,Bishop, P.J. 2012. A second species of Tristichopterus (Sarcopterygii: Tristichopteridae), from the Upper Devonian ...

'' and ''

Eusthenodon ''Eusthenodon'' (Greek for “strong-tooth” – ''eusthenes''- meaning “strong”, -''odon'' meaning “tooth”) is an extinct genus of marine tristichopterid tetrapodomorphs from the Devonian, Late Devonian period, ranging between 365 and 3 ...

''. ''Eusthenopteron'' was widespread throughout what is now considered the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

(which was located around the

Equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

at the time), and at least seven to eight species are known from Eurasia and North America. The following species list is based on Downs, Daeschler, Long & Shubin (2018): * †''E. farloviensis''

White White is the lightest color and is achromatic (having no chroma). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully (or almost fully) reflect and scatter all the visible wa ...

, 1961 - Frasnian of England * †''E. foordi'' Whiteaves, 1881 (

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

) - Frasnian of Quebec, Canada ( Escuminac Formation in Miguasha National Park). Named after Arthur Humphreys Foord. * †''E. jenkinsi'' Downs, Daeschler, Long & Shubin, 2018 - Frasnian of Nunavut, Canada ( Fram Formation). Named after Farish Jenkins. * †''E. kurshi'' Zupiņš, 2008 - late Givetian of

Latvia Latvia, officially the Republic of Latvia, is a country in the Baltic region of Northern Europe. It is one of the three Baltic states, along with Estonia to the north and Lithuania to the south. It borders Russia to the east and Belarus to t ...

( Lode Formation) * †''E. obruchevi'' Vorobyeva, 1977 -

late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

of Latvia. Named after Vladimir Obruchev. * †''E. saevesoederberghi'' Jarvik, 1937 - Frasnian of Latvia ( Pļaviņas Formation). Named after Gunnar Säve-Söderbergh * †''E. traquairi'' Westoll, 1937 - Frasnian of Elgin, Scotland. Named after Ramsay Traquair. * †''E. wenjukowi'' ( Rohon, 1889) - Frasnian of

Leningrad Oblast Leningrad Oblast (, ; ; ) is a federal subjects of Russia, federal subject of Russia (an oblast). The oblast has an area of and a population of 2,000,997 (2021 Russian census, 2021 Census); up from 1,716,868 recorded in the 2010 Russian census ...

, Russia (=''Cricodus wenjukowi'' Rohon, 1889, ''Jarvikina'' Vorobyeva, 1977) The species ''E. wenjukowi'' was moved to its own genus, ''Jarvikina'', in 1977 based on apparent morphological differences from ''Eusthenopteron'', although this classification has been disputed. The species ''E. jenkinisi'', described in 2018, indicates that ''Eusthenopteron'' may have been more morphologically variable than previously assumed, which further supports placing ''wenjukowi'' back in ''Eusthenopteron''. The former species ''E. dalgleisiensis'' is now placed in its own genus, '' Heddleichthys''.

Description

''Eusthenopteron'' is a medium- to large-sized tristichopterid. The species ''E. foordi'' is estimated to have exceeded in length, while the species ''E. jenkinsi'' probably reached . ''Eusthenopteron'' may have weighed around 50 kilograms. The earliest known fossilized evidence of

bone marrow Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...

has been found in ''Eusthenopteron'', which may be the origin of bone marrow in tetrapods.Sanchez S, Tafforeau P and Ahlberg P E (2014
"The humerus of Eusthenopteron: a puzzling organization presaging the establishment of tetrapod limb bone marrow"
''Proceedings of the Royal Society B: Biological Sciences'', 281 (1782): 20140299. Eusthenopteron foordi 1

''Eusthenopteron'' shares many unique features among fishes but in common with the earliest-known

s. It shares a similar pattern of skull roofing bones with

stem tetrapoda The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives (the lungfish), but excluding the crown group Tetrapoda. They are thus ...

forms such as ''

Ichthyostega ''Ichthyostega'', from Ancient Greek ἰχθύς (''ikthús''), meaning "fish", and στέγη (''stégē''), meaning "roof", is an Extinction, extinct genus of limbed tetrapodomorpha, tetrapodomorphs from the Devonian, Late Devonian of what is ...

'' and ''

Acanthostega ''Acanthostega'', from Ancient Greek ἄκανθα (''ákantha''), meaning "spine", and στέγη (''stégē''), meaning "roof", is an extinct genus of stem tetrapoda, stem-tetrapod, among the first vertebrates, vertebrate animals to have recogn ...

''. ''Eusthenopteron'', like other

tetrapodomorph Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced for ...

fishes, had internal

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

s (or a

choana The choanae (: choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the pharynx, in humans and other mammals (as well as crocodilians and most skinks). They ...

), one of the defining traits of tetrapodomorphs, including tetrapods. It also had

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally conside ...

teeth, characterized by infolded enamel, which characterizes all of the earliest known tetrapods as well. Unlike the early tetrapods, ''Eusthenopteron'' did not have larval

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s.Amphibian evolution : the life of early land vertebrates (page 141)
/ref>

Anatomy

Like other fish-like sarcopterygians, ''Eusthenopteron'' possessed a two-part

cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, which hinged at mid-length along an intracranial joint. ''Eusthenopteron''s notoriety comes from the pattern of its fin

endoskeleton An endoskeleton (From Ancient Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is a structural frame (skeleton) — usually composed of mineralized tissue — on the inside of an animal, overlaid by soft ...

, which bears a distinct

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, and

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

in the fore-fin and

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

, and

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

in the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

. These appendicular long bones had epiphyseal growth plates that allowed substantial longitudinal growth through

endochondral ossification Endochondral ossification is one of the two essential pathways by which bone tissue is produced during fetal development and bone healing, bone repair of the mammalian skeleton, skeletal system, the other pathway being intramembranous ossificatio ...

, as in tetrapod long bones.M. Laurin, F. and J. Meunier 2012. A microanatomical and histological study of the fin long bones of the Devonian sarcopterygian ''Eusthenopteron foordi. Acta Zoologica'' 93: 88–97. These six appendicular bones also occur in tetrapods and are a

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

of a large

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of sarcopterygians, possibly

Tetrapodomorpha Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced f ...

(the humerus and femur are present in all sarcopterygians). Similarly, its elasmoid scales lack superficial odontodes composed of dentine and enamel; this loss appears to be a synapomorphy with more crownward tetrapodomorphs.Zylberberg, L., Meunier, F. J. and Laurin, M. 2010. A microanatomical and histological study of the postcranial dermal skeleton in the Devonian sarcopterygian ''Eusthenopteron foordi
Acta Palaeontologica Polonica
' 55: 459–470. ''Eusthenopteron'' differs significantly from some later

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

tetrapods in the apparent absence of a recognized

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l stage and a definitive

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

.Schultze, H.-P. 1984. Juvenile specimens of ''Eusthenopteron foordi'' Whiteaves, 1881 (Osteolepiform rhipidistian, Pisces) from the Late Devonian of Miguasha, Quebec, Canada. ''Journal of Vertebrate Paleontology'' 4: 1-16. In even the smallest known specimen of ''Eusthenopteron foordi'', with a length of , the

lepidotrichia In a zoological context, spines are hard, needle-like anatomical structures found in both vertebrate and invertebrate species. The spines of most spiny mammals are modified hairs, with a spongy center covered in a thick, hard layer of keratin and ...

cover all of the fins, which does not happen until after metamorphosis in genera like ''Polydon'' (the

American paddlefish The American paddlefish (''Polyodon spathula''), also known as a Mississippi paddlefish, spoon-billed cat, or spoonbill, is a species of ray-finned fish. It is the last extant taxon, living species of paddlefish (Polyodontidae). This family is ...

). This might indicate that ''Eusthenopteron'' developed directly, with the

hatchling In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well. Fish Fish hatchlings generally do not receive parental care, similar t ...

already attaining the adult's general body form (Cote et al., 2002). Fishapods

References

External links

Palaeos.com – Vertebrates – Sarcopterygii
(archive) {{Taxonbar, from=Q133383 Tristichopteridae Prehistoric lobe-finned fish genera Late Devonian sarcopterygians Devonian sarcopterygians of North America Devonian sarcopterygians of Europe Givetian life Frasnian genera Fossils of Canada Fossils of Great Britain Fossils of Latvia Fossils of Russia Transitional fossils Taxa named by Joseph Frederick Whiteaves Fossil taxa described in 1881

Taxonomy

Description

Anatomy

See also

References

External links