Eusthenopteron

Taxobox
name = "Eusthenopteron"
fossil_range = Late Devonian

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image_width = 240px
image_caption = life restoration of "Eusthenopteron foordi"
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
classis = Sarcopterygii
subclassis = Tetrapodomorpha
superordo = Osteolepidida
familia = Tristichopteridae
genus = "Eusthenopteron"
genus_authority = Whiteaves, 1881
subdivision_ranks = Species
subdivision =
* "E. foordi" (type)
* "E. savesoderberghi"
* "E. waengsjoei"
* "E. wenjukowi"

"Eusthenopteron" is a genus of prehistoric lobe-finned fish 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 pelagic animal. 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.

Anatomically, "Eusthenopteron" shares many unique features in common with the earliest known tetrapods. It shares a similar pattern of skull rooting bones with forms such as Ichthyostega and Acanthostega. "Eusthenopteron", like other tetrapodomorph fishes, had internal nostrils, (or a choana) which are found only in land animals and sarcopterygians. It also had labyrinthodont teeth, characterized by infolded enamel, which characterizes all of the earliest known Tetrapods as well. Like other basal 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, which bears a distinct humerus, ulna, and radius (in the fore-fin) and femur, tibia, and fibula (in the pelvic fin). This is the characteristic pattern seen in tetrapods. It is now known to be a general character of fossil sarcopterygian fins.

– like "Eusthenopteron" – exhibited a sequence of adaptations:

• "Panderichthys", suited to muddy shallows;
• "Tiktaalik" with limb-like fins that could take it onto land;
• Early tetrapods in weed-filled swamps, such as:
  • "Acanthostega" which had feet with eight digits,
  • "Ichthyostega" with limbs.

Descendants also included pelagic lobe-finned fish such as coelacanth species.]

"Eusthenopteron" differs significantly from later Carboniferous tetrapods in the apparent absence of a recognized larval stage and a definitive metamorphosis. 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 general body form of the adult (Cote et. al, 2002).

ee also

* "Tiktaalik", an even more tetrapod-like sarcopterygian.
* "Gogonasus"

References

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External References

* http://www.palaeos.com/Vertebrates/Units/140Sarcopterygii/140.860.html