Eusthenodon

In 1952, Swedish paleontologist Erik Jarvik first described the first species, Eusthenodon wangsjoi of the genus Eusthenodon. The specimen was retrieved in 1936 from the richly fossiliferous sediments of the Upper Devonian sequences of East Greenland, a region that gained tremendous attraction by vertebrate paleontologists after the discovery of the early limbed vertebrate Ichthyostega. == Taxonomy ==

The following species are placed in this genus: • †E. bourdoni Downs et al., 2021- Late Famennian of Pennsylvania, USA (Catskill Formation) and New South Wales, Australia (Hunter Siltstone) The alleged species "E. gavini" Johanson & Ritchie, 2000 from the Hunter Siltstone of Australia is only known from very fragmentary material that cannot be confidently assigned to this genus, and likely requires revision. Classification Eusthenodon belongs to the family Tristichopteridae, a subdivision of the order Osteolepiformes within the greater class of Sarcopterygii. Sarcopterygii is the major clade that diverted from the ray-finned Actinopterygii with the evolution of lobed-fins. The phylogeny of Tristichopteridae was described by Gael Clement, Daniel Snitting, and P.E. Ahlberg (2008) after performing a maximum parsimony analysis of the interrelationships of within the clade: }} == Description ==

Skull In his initial diagnosis of the first Eusthenodon remains published in 1952, Jarvik describes the features present in the remains of Eusthenodon wangsjoi including those that are significant characters of tristichopterid fishes (referred to as rhizodontids by Jarvik) as well as the traits unique to the described species and diagnostic characters of the genus. Furthermore, each of these round cosmineless scales include a proximal central attachment boss, also diagnostic of Tristichopteridae. In contrast to most other tristichopterids, the ornamentation of Eusthenodon scales exhibit ridges forming distinct networks whereas scales from Eusthenopteron tend to have an ornamentation of considerably shorter ridges present in the incompletely fused tubercles. The area of overlap between scales in Eusthenodon is also larger than the scales of Eusthenopteron. == References ==