''Eusthenopteron'' (from el, εὖ , 'good', el, σθένος , 'strength', and el, πτερόν 'wing' or 'fin') is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of prehistoric sarcopterygian (often called

lobe-finned fish Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

es) which has attained an iconic status from its close relationships to

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s. Early depictions of this animal show it emerging onto land; however,

paleontologists Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

now widely agree that it was a strictly aquatic

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

.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 ''Eusthenopteron'' is known from several species that lived during the Late Devonian period, about 385 million years ago. ''Eusthenopteron'' was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha, Quebec. Some 2,000 ''Eusthenopteron'' specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers from the 1940s to the 1990s by paleoichthyologist

Erik Jarvik Anders Erik Vilhelm Jarvik (30 November 1907 – 11 January 1998) was a Swedish paleontologist who worked extensively on the sarcopterygian (or lobe-finned) fish ''Eusthenopteron''. In a career that spanned some 60 years, Jarvik produced some ...

Description

The earliest-known fossilized evidence of bone marrow 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'' shares many unique features in common with the earliest-known

s. It shares a similar pattern of skull roofing bones with forms such as '' Ichthyostega'' and ''

Acanthostega ''Acanthostega'' (meaning "spiny roof") is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period (Famennian age) about 365 million years ago, and was anatomic ...

''. ''Eusthenopteron'', like other tetrapodomorph fishes, had internal nostrils, (or a

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

) which are one of the defining traits of tetrapodomorphs (including tetrapods). It also had labyrinthodont teeth, characterized by infolded enamel, which characterizes all of the earliest known tetrapods as well.

Classification

Like other fish-like sarcopterygians, ''Eusthenopteron'' possessed a two-part cranium, which hinged at mid-length along an intracranial joint. ''Eusthenopteron''s notoriety comes from the pattern of its fin

endoskeleton An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue. Overview An endoskeleton is a skeleton that is on the ...

, which bears a distinct humerus, ulna, and radius (in the fore-fin) and femur, tibia, and fibula (in the pelvic fin). These appendicular long bones had epiphyseal growth plates that allowed substantial longitudinal growth through endochondral ossification, 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 character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

of a large clade of sarcopterygians, possibly

Tetrapodomorpha The Tetrapodomorpha (also known as Choanata) are 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. Advance ...

(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 tetrapods in the apparent absence of a recognized larval stage and a definitive metamorphosis.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'' (at 29 mm), the

lepidotrichia 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 see ...

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

Polyodon 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 only living species of paddlefish (Polyodontidae). This family is most closely r ...

''. This might indicate that ''Eusthenopteron'' developed directly, with the hatchling already attaining the adult's general body form (Cote et al., 2002).

References

External links

* https://web.archive.org/web/20060313170715/http://www.palaeos.com/Vertebrates/Units/140Sarcopterygii/140.860.html {{Taxonbar, from=Q133383 Tristichopterids Extinct animals of North America Prehistoric lobe-finned fish genera Devonian bony fish Late Devonian animals Late Devonian fish Transitional fossils

Description

Classification

See also

References

External links