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

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of ...

sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its close relationships to tetrapods. Early depictions of this animal show it emerging onto land; however, paleontologists now widely agree that it was a strictly aquatic animal.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 The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

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 The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish ...

Erik Jarvik.

Description

The earliest-known fossilized evidence of

bone marrow Bone marrow is a semi-solid tissue found within the 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 is composed of hematopoietic ce ...

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 tetrapods. It shares a similar pattern of skull roofing bones with forms such as ''

Ichthyostega ''Ichthyostega'' (from el, ἰχθῦς , 'fish' and el, στέγη , 'roof') is an extinct genus of limbed tetrapodomorphs from the Late Devonian of Greenland. It was among the earliest four-limbed vertebrates in the fossil record, and was on ...

'' and '' Acanthostega''. ''Eusthenopteron'', like other tetrapodomorph fishes, had internal nostrils, (or a choana) which are 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 consid ...

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 The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

, which hinged at mid-length along an

intracranial joint The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull minus the mandible is called the ''cranium''. The cavity is formed by eight cranial bones known as the neurocranium that in ...

. ''Eusthenopteron''s notoriety comes from the pattern of its fin endoskeleton, 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 Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is produced. Unlike intramembranous ossification, the other process by which bone tissue is produced, c ...

, 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 of a large clade of sarcopterygians, possibly Tetrapodomorpha (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 period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

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