Eotetrapodiformes
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This clade is defined as "the node-based clade arising from the most recent common ancestor of Eusthenopteron and Ichthyostega plus all of its descendants," for their litany of shared morphological characteristics, such as similarities in their lower jaws and endocrania. Utilizing the holotype FMNH PF 610 of the sarcopterygian Litoptychus bryanti, paleontologists highlighted the division between the ethmoid and sphenoid processes, as well as vomeral and parasphenoid processes similar to those of more derived tetrapods. Eotetrapodiformes are considered a sister taxon to Megalichthyiformes and Rhizodontida.
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History
The clade was named in 2010 by Michael I. Coates and Matt Friedman.
Paleoecology
Biogeography
The majority of eotetrapodimorphs have been discovered from formations from southern Euramerica. The earliest tetrapodomorphs are known from China and Australia, from a time where relatively few examples have been discovered outside of East Asia and eastern Gondwana.
Evolution
Ancestry
Families described in this clade evolved in the lower Devonian period 400 to 5 million years ago. And evolved into other different species. Most of the geological stages that have the highest recorded number of formations are restricted to southern Euramerica where the majority of eotetrapodiform taxa have been discovered. In Coates and Friedman's seminal paper defining eotetrapodiformes as separate from megalichthyiformes and rhizodontids, they hypothesized that though each clade diversified considerable throughout the Devonian, only the limbed tetrapods survived beyond.
Cladogram from Swartz, 2012: