Eusthenopteron

 ( Tristichopteridae ) 

Eusthenopteron (from 'stout', and 'wing' or 'fin') is an extinct genus of Prehistory marine Sarcopterygii known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic status from its close relationship to . Early depictions of animals of this genus show them emerging onto land, but Paleontology now think that Eusthenopteron species were strictly aquatic , 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, Canada. 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, which has also been alternatively named Eusthenopteridae after this genus. It is related to genera such as Tristichopterus and Eusthenodon.

(2025). 9781119286431, Wiley-Blackwell. . ISBN 9781119286431

Eusthenopteron was widespread throughout what is now considered the Northern Hemisphere (which was located around the Equator 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 Errol White, 1961 - Frasnian of England
• † E. foordi Whiteaves, 1881 (type species) - Frasnian of Quebec, Canada (Escuminac Formation in Miguasha National Park). Named after Arthur Humphreys Foord.
• † E. jenkinsi Downs, Ted Daeschler, Long & Neil Shubin, 2018 - Frasnian of Nunavut, Canada (Fram Formation). Named after Farish Jenkins.
• † E. kurshi Zupiņš, 2008 - late Givetian of Latvia (Lode Formation)
• † E. obruchevi Emilia Vorobyeva, 1977 - Devonian of Latvia. Named after Vladimir Obruchev.
• † E. saevesoederberghi Erik 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, 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., Quebec (Canada). At the Royal Tyrrell Museum of Palaeontology.|223x223px]]

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 among fishes but in common with the earliest-known . It shares a similar pattern of Skull roof with stem tetrapoda forms such as Ichthyostega and Acanthostega. Eusthenopteron, like other Tetrapodomorpha fishes, had internal (or a choana), one of the defining traits of tetrapodomorphs, including tetrapods. It also had Mastodonsaurus teeth, characterized by infolded Tooth enamel, which characterizes all of the earliest known tetrapods as well.

Unlike the early tetrapods, Eusthenopteron did not have larval . Amphibian evolution : the life of early land vertebrates (page 141)

---

Anatomy

]]Like other fish-like sarcopterygians, Eusthenopteron possessed a two-part Skull, which hinged at mid-length along an intracranial joint. Eusthenopterons notoriety comes from the pattern of its Fish 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 plate 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 of a large clade of sarcopterygians, possibly Tetrapodomorpha (the humerus and femur are present in all sarcopterygians). Similarly, its Fish scale lack superficial 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 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, with a length of , the lepidotrichia cover all of the fins, which does not happen until after metamorphosis in genera like Polydon (the American paddlefish). This might indicate that Eusthenopteron developed directly, with the hatchling already attaining the adult's general body form (Cote et al., 2002). vertebrate speciation, descendants of Pelagic zone Sarcopterygii—like Eusthenopteron—exhibited a sequence of adaptations:

• Panderichthys, suited to muddy shallows;
• Tiktaalik with limb-like fins that could take it onto land;
• Early 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.|center]]

---

See also

• Gogonasus
• Tiktaalik – an even more tetrapod-like sarcopterygian

---

External links

• Palaeos.com – Vertebrates – Sarcopterygii (archive)

Categories: 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