Rhytidostea
Encyclopedia
Rhytidostea is a clade
of stereospondyl temnospondyls. It was erected in 2000 to include several temnospondyl groups distinct from the "higher" group of capitosaurs, including lydekkerinids
, brachyopoids
, and rhytidosteids
. Rhytidosteans first appeared in the Permian
period and underwent an evolutionary radiation during the Induan
stage of the Early Triassic
. Along with capitosaurs, rhytidosteans comprise much of the larger suborder Stereospondyli. Rhytidostea has often been considered the sister group of the clade Capitosauria
, but has been placed in various other phylogenetic positions. In many studies, members of Rhytidostea are split, with lydekkerinids having a more basal position among stereospondyls while rhytidosteids and brachyopoids form a group placed among the more derived trematosauria
n stereospondyls.
(a brachyopid), and all descendants of their most recent common ancestor
. Below is a cladogram
modified from Ruta et al. (2007):
Other phylogenetic analyses have placed rhytidosteids and brachyopoids as closely related groups within Trematosauria
, a more derived clade of stereospondyls. They are separate from the lydekkerinids, which remain a basal group of stereospondyls.
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...
of stereospondyl temnospondyls. It was erected in 2000 to include several temnospondyl groups distinct from the "higher" group of capitosaurs, including lydekkerinids
Lydekkerinidae
Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Triassic period. During the Triassic, lydekkerinids had a global distribution. They were small-bodied with wedge-shaped, roughly triangular heads. Fossils have been found in Russia, Greenland, India, South Africa,...
, brachyopoids
Brachyopoidea
Brachyopoidea is a superfamily of temnospondyls that lived during the Mesozoic. It contains the families Brachyopidae and Chigutisauridae. The earliest records of brachyopids are from the Lower Triassic in Australia...
, and rhytidosteids
Rhytidosteidae
Rhytidosteidae is a family of Temnospondyli that lived in the Permian and Triassic.-References:*Yates, AM , A new tiny rhytidosteid from the Early Triassic of Australia and the possibility of hidden temnospondyl diversity. J. Vert Paleontol. 20:484-489.-External links:*...
. Rhytidosteans first appeared 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 and underwent an evolutionary radiation during the Induan
Induan
The Induan is, in the geologic timescale, the first age of the Early Triassic epoch or the lowest stage of the Lower Triassic series. It spans the time between 251 ± 0.4 Ma and 249.7 ± 0.7 Ma...
stage of the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
. Along with capitosaurs, rhytidosteans comprise much of the larger suborder Stereospondyli. Rhytidostea has often been considered the sister group of the clade Capitosauria
Capitosauria
Capitosauria is a clade of stereospondyl temnospondyls. Capitosauria and its sister taxon Trematosauria are the only major temnospondyl clades that existed during the Mesozoic....
, but has been placed in various other phylogenetic positions. In many studies, members of Rhytidostea are split, with lydekkerinids having a more basal position among stereospondyls while rhytidosteids and brachyopoids form a group placed among the more derived trematosauria
Trematosauria
Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other being the Capitosauria. The trematosaurs were a diverse and important group that included many medium-sized to large forms that were semi-aquatic to totally aquatic...
n stereospondyls.
Classification
Schoch and Milner (2000) erected the clade Rhytidostea to include lydekkerinids, brachyopoids, and rhytidosteids. The clade was the sister taxon of Capitosauria, the "higher" stereospondyls. Ruta et al. (2007) placed Rhytidostea in a similar phylogenetic position, defining it as a clade including Eolydekkerina (a lydekkerinid), BatrachosuchusBatrachosuchus
Batrachosuchus is an extinct genus of temnospondyl amphibian from the Triassic of South Africa.-Sources:*Wildlife of Gondwana: Dinosaurs and Other Vertebrates from the Ancient Supercontinent by Pat Vickers Rich, Thomas Hewitt Rich, Francesco Coffa, and Steven Morton...
(a brachyopid), and all descendants of their most recent common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
. 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...
modified from Ruta et al. (2007):
Other phylogenetic analyses have placed rhytidosteids and brachyopoids as closely related groups within Trematosauria
Trematosauria
Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other being the Capitosauria. The trematosaurs were a diverse and important group that included many medium-sized to large forms that were semi-aquatic to totally aquatic...
, a more derived clade of stereospondyls. They are separate from the lydekkerinids, which remain a basal group of stereospondyls.