Dvinosauria
Encyclopedia
Dvinosaurs are one of several new clade
s of Temnospondyl
amphibians named in the phylogenetic
review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from the Late Carboniferous to the Early Triassic, being most common in the Permian
period. Their distinguishing characteristics are a reduction of the otic notch
; 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, representing a grade of basal dvinosauroids. Below is a cladogram
showing the phylogenetic relationships of dvinosaurs from Englehorn et al. (2008):
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s of Temnospondyl
Temnospondyli
Temnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent...
amphibians named in the phylogenetic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from the Late Carboniferous to the Early Triassic, being most common in the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
period. Their distinguishing characteristics are a reduction of the otic notch
Otic notch
Otic notches are invagination in the posterior margin of the skull roof, one behind each orbit. Such notches are found in labyrinthodonts and some of their immediate ancestors, but not their reptilian descendants...
; the loss of a flange on the rear side of the pterygoid
Pterygoid
Pterygoid can refer to:* Pterygoid processes of the sphenoid bone** The Lateral pterygoid plate by it* a muscle such as Lateral pterygoid muscle or Medial pterygoid muscle* a branch of the Mandibular nerve...
; and 28 or more presacral vertebrae.
Trimerorhachidae
Trimerorhachidae
Trimerorhachidae is a family of dvinosaurian temnospondyls....
is the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
family of dvinosaurs. Most other dvinosaurs are placed in the superfamily Dvinosauroidea. Within Dvinosauroidea are two families, Eobrachyopidae
Eobrachyopidae
Eobrachyopidae is a family of dvinosaurian temnospondyls....
and Tupilakosauridae
Tupilakosauridae
Tupilakosauridae is an extinct family of dvinosaurian temnospondyls. It contains the genera Slaugenhopia, Thabanchuia, Tupilakosaurus, and possibly Kourerpeton. Tupilakosaurs are known from Texas, Greenland, Russia, and France. The earliest tupilakosaur, Slaugenhopia, is Early Permian in age while...
, as well as dvinosaurs that cannot be placed in either family, such as Dvinosaurus
Dvinosaurus
Dvinosaurus is a genus of extinct temnospondyl amphibian from the Late Permian of Russia. The first three species, D. primus , D. secundus, and D. tertius, were described by Russian paleontologist Vladimir Prokhorovich Amalitskii in 1921...
and Kourerpeton
Kourerpeton
Kourerpeton is an extinct genus of dvinosaurian temnospondyl. Fossils of Kourerpeton were discovered in a window of a barber's shop in either Bisbee or Mesa, Arizona. Kourerpeton was named in 1976, with the type and only species being K. bradyi...
. A 2008 phylogenetic analysis found Eobrachyopidae to be paraphyletic, representing a grade of basal dvinosauroids. Below is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
showing the phylogenetic relationships of dvinosaurs from Englehorn et al. (2008):
Links
- Temnospondyli: Limnarchia at Palaeos
- Dvinosauria at Mikko's Phylogeny Archive (cladogram based on Yates and Warren 2000)
- Suborder †Dvinosauria - Scientific Hierarchy at the Taxonomicon