| Eusthenopteron | |
|---|---|
 | |
| Life restoration ofE. foordi | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sarcopterygii |
| Clade: | Tetrapodomorpha |
| Clade: | Eotetrapodiformes |
| Family: | †Tristichopteridae |
| Genus: | †Eusthenopteron Whiteaves, 1881 |
| Type species | |
| †Eusthenopteron foordi Whiteaves, 1881 | |
| Species[1] | |
See text | |
| Synonyms | |
| |
Eusthenopteron (fromGreek:εὖσθένοςeûsthénos 'stout', andGreek:πτερόνpteron 'wing' or 'fin')[2][1] is an extinctgenus ofprehistoric marinelobe-finned fish known from severalspecies that lived during the LateDevonianperiod, about 385 million years ago. It has attained an iconic status from its close relationship totetrapods. Early depictions of animals of this genus show them emerging onto land, butpaleontologists now think thatEusthenopteron species were strictly aquaticanimals, though this is not completely known.[3]
The genus was first described byJ. F. Whiteaves in 1881, as part of a large collection of fishes fromMiguasha,Quebec,Canada.[4] Some 2,000Eusthenopteron specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers bypaleoichthyologistErik Jarvik between the 1940s and the 1990s.[5] Further species have been described from other parts of Canada and northern Europe, indicating that this genus had a wide distribution.[1]
Eusthenopteron is placed in the familyTristichopteridae, which has also been alternatively namedEusthenopteridae after this genus. It is related to genera such asTristichopterus andEusthenodon.[6]
Eusthenopteron was widespread throughout what is now considered theNorthern Hemisphere (which was located around theEquator 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):[1][7]
The speciesE. wenjukowi was moved to its own genus,Jarvikina, in 1977 based on apparent morphological differences fromEusthenopteron, although this classification has been disputed. The speciesE. jenkinisi, described in 2018, indicates thatEusthenopteron may have been more morphologically variable than previously assumed, which further supports placingwenjukowi back inEusthenopteron.[1] The former speciesE. dalgleisiensis is now placed in its own genus,Heddleichthys.[11]
Eusthenopteron is a medium- to large-sizedtristichopterid. The speciesE. foordi is estimated to have exceeded 1.5 m (4 ft 11 in) in length, while the speciesE. jenkinsi probably reached 2.1 m (6 ft 11 in).[12][1]Eusthenopteron may have weighed around 50 kilograms.[13]
.jpg)
The earliest known fossilized evidence ofbone marrow has been found inEusthenopteron, which may be the origin of bone marrow in tetrapods.[14]
Eusthenopteron shares many unique features among fishes but in common with the earliest-knowntetrapods. It shares a similar pattern ofskull roofing bones withstem tetrapoda forms such asIchthyostega andAcanthostega.Eusthenopteron, like othertetrapodomorph fishes, had internalnostrils (or achoana), one of the defining traits of tetrapodomorphs, including tetrapods. It also hadlabyrinthodont teeth, characterized by infoldedenamel, which characterizes all of the earliest known tetrapods as well.
Unlike the early tetrapods,Eusthenopteron did not have larvalgills.[15]
 | This sectionmay be too technical for most readers to understand. Pleasehelp improve it tomake it understandable to non-experts, without removing the technical details.(February 2018) (Learn how and when to remove this message) |
Like other fish-like sarcopterygians,Eusthenopteron possessed a two-partcranium, which hinged at mid-length along anintracranial joint.Eusthenopteron's notoriety comes from the pattern of itsfinendoskeleton, which bears a distincthumerus,ulna, andradius in the fore-fin andfemur,tibia, andfibula in thepelvic fin. Theseappendicular long bones hadepiphyseal growth plates that allowed substantial longitudinal growth throughendochondral ossification, as in tetrapod long bones.[16] These six appendicular bones also occur in tetrapods and are asynapomorphy of a largeclade of sarcopterygians, possiblyTetrapodomorpha (the humerus and femur are present in all sarcopterygians). Similarly, itselasmoid scales lack superficialodontodes composed ofdentine and enamel; this loss appears to be a synapomorphy with more crownward tetrapodomorphs.[17]Eusthenopteron differs significantly from some laterCarboniferous tetrapods in the apparent absence of a recognizedlarval stage and a definitivemetamorphosis.[12] In even the smallest known specimen ofEusthenopteron foordi, with a length of 29 millimetres (1.1 in), thelepidotrichia cover all of the fins, which does not happen until after metamorphosis in genera likePolydon (theAmerican paddlefish). This might indicate thatEusthenopteron developed directly, with thehatchling already attaining the adult's general body form (Cote et al., 2002).
| |||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||
.jpg)
.jpg)
