Dvinosaurs are one of several new

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 ...

s of

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

s named in the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic temnospondyls, and are known from the Late Carboniferous to the Early Triassic, being most common in the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

period. Their distinguishing characteristics are a reduction of the

otic notch Otic notches are invaginations in the posterior margin of the skull roof, one behind each orbit. Otic notches are one of the features lost in the evolution of amniotes from their tetrapod ancestors. The notches have been interpreted as part of an ...

; the loss of a flange on the rear side of the pterygoid; and 28 or more presacral vertebrae. Trimerorhachidae is the most basal family of dvinosaurs. Most other dvinosaurs are placed in the superfamily Dvinosauroidea. Within Dvinosauroidea are two families, Eobrachyopidae and Tupilakosauridae, as well as dvinosaurs that cannot be placed in either family, such as '' Dvinosaurus'' and '' Kourerpeton''. A 2008 phylogenetic analysis found Eobrachyopidae to be

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

, representing a grade of basal dvinosauroids. Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing the phylogenetic relationships of dvinosaurs from Englehorn ''et al.'' (2008):

References

* Laurin, M. and Steyer, J-S (2000) Phylogeny and Apomorphies of Temnospondyls. , The Tree of Life Web Project *

External links

Temnospondyli: Limnarchia
at Palaeos

at Mikko's Phylogeny Archive (cladogram based on Yates and Warren 2000)
Suborder †Dvinosauria
- Scientific Hierarchy at the Taxonomicon Carboniferous temnospondyls Permian temnospondyls Triassic temnospondyls Pennsylvanian first appearances Early Triassic extinctions Prehistoric animal suborders {{temnospondyli-stub