Eotetrapodiformes is an unranked

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

tetrapodomorph Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced for ...

s including the four-limbed vertebrates ("

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s" in the traditional sense) and their closest finned relatives, two groups of

stem tetrapod The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives (the lungfish), but excluding the crown group Tetrapoda. They are thus ...

s called tristichopterids and

elpistostegalid Elpistostegalia is a clade containing ''Panderichthys'' and all more derived tetrapodomorph taxa. The earliest elpistostegalians, combining fishlike and tetrapod-like characters, such as ''Tiktaalik'', are sometimes called fishapods. Although hi ...

Description

This clade is defined as "the node-based clade arising from the most recent common ancestor of ''

Eusthenopteron ''Eusthenopteron'' (from 'stout', and 'wing' or 'fin') is an extinct genus of prehistoric marine lobe-finned fish known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic ...

'' and ''

Ichthyostega ''Ichthyostega'', from Ancient Greek ἰχθύς (''ikthús''), meaning "fish", and στέγη (''stégē''), meaning "roof", is an Extinction, extinct genus of limbed tetrapodomorpha, tetrapodomorphs from the Devonian, Late Devonian of what is ...

'' plus all of its descendants," for their litany of shared morphological characteristics, such as similarities in their lower jaws and endocrania. Utilizing the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

FMNH PF 610 of the

sarcopterygian Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

''Litoptychus bryanti,'' paleontologists highlighted the division between the

ethmoid The ethmoid bone (; from ) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbit (anatomy), orbits. The cubical (cube-shaped) bone is lightweight due to a sp ...

and sphenoid processes, as well as

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

al and

parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived ...

processes similar to those of more derived tetrapods. Eotetrapodiformes are considered a sister taxon to

Megalichthyiformes Megalichthyiformes is an extinct clade of basal tetrapodomorphs which first appeared during the Devonian period. It was named in 2010 by Michael I. Coates and Matt Friedman, who defined it as a stem-based taxon containing all tetrapodomorphs clo ...

and

Rhizodontida Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizod ...

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 Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

. 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 considerably throughout the Devonian, only the limbed tetrapods survived beyond. Cladogram from Swartz, 2012:

References

{{Taxonbar, from=Q5381965 Extant Devonian first appearances Evolution of tetrapods