Stereospondyli
Encyclopedia
The Stereospondyli are a group of extinct temnospondyl
amphibian
s. Relative to other early tetrapods (labyrinthodonts), they had simplified backbones, where the whole vertebra was made of a single intercentrum, topped by a neural arch. The whole vertebral structure was rather weak, meaning that most stereospondyls were aquatic. Indeed, the family Plagiosauridae
appear to have been wholly aquatic and retained their larval gill
s in adulthood.
Stereospondyls first appeared during the Late Permian. During this time, the two major groups of stereospondyls, capitosauria
ns and trematosauria
ns, appeared. Stereospondyls were relatively uncommon in the Paleozoic
, outnumbered by the more diverse euskelia
ns. During this time, they were endemic to Gondwana. Many early groups of temnospondyls went extinct during the Permian-Triassic extinction event
but stereospondyls likely survived in Australia
or Antarctica, radiating worldwide in the Triassic
.
Stereospondyls were the latest-surviving temnospondyl group. With the diversification of crocodile-like archosaur
s and an extinction event
at the end of the Triassic, most other temnospondyls disappeared. Two families of stereospondyls survived into the Jurassic
, and some appear to have survived into the Early Cretaceous
in Gondwana
. Koolasuchus
is the latest known stereospondyl, living during the late Early Cretaceous in what is now Australia
in areas that would then have been too cold for crocodiles.
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...
amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s. Relative to other early tetrapods (labyrinthodonts), they had simplified backbones, where the whole vertebra was made of a single intercentrum, topped by a neural arch. The whole vertebral structure was rather weak, meaning that most stereospondyls were aquatic. Indeed, the family Plagiosauridae
Plagiosauridae
Plagiosauridae is a family of Temnospondyli that lived in the Triassic period.-References:*Milner, A.R. 1994, Late Triassic and Jurassic amphibians: fossil record and phylogeny, pp. 5-22 in Fraser & Sues In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods, Cambridge University Press,...
appear to have been wholly aquatic and retained their larval gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s in adulthood.
Stereospondyls first appeared during the Late Permian. During this time, the two major groups of stereospondyls, 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....
ns and 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...
ns, appeared. Stereospondyls were relatively uncommon in the Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
, outnumbered by the more diverse euskelia
Euskelia
Euskelia is a clade of extinct Temnospondyl amphibians.-References:*Yates, A. M. & Warren, A. A. , The phylogeny of the 'higher' temnospondyls and its implications for the monophyly and origins of the Stereospondyli. Zoological Journal of the Linnean Society 128: 77-121....
ns. During this time, they were endemic to Gondwana. Many early groups of temnospondyls went extinct during the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
but stereospondyls likely survived in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
or Antarctica, radiating worldwide in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
.
Stereospondyls were the latest-surviving temnospondyl group. With the diversification of crocodile-like archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s and an extinction event
Triassic-Jurassic extinction event
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, , and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas a whole class and twenty percent of all marine families...
at the end of the Triassic, most other temnospondyls disappeared. Two families of stereospondyls survived into the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, and some appear to have survived into the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
in Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
. Koolasuchus
Koolasuchus
Koolasuchus is an extinct genus of brachyopoid temnospondyl in the family Chigutisauridae. Fossils have been found from Victoria, Australia and date back 120 Ma to the Aptian stage of the Early Cretaceous. Koolasuchus is the latest known temnospondyl. Koolasuchus is known from several fragments of...
is the latest known stereospondyl, living during the late Early Cretaceous in what is now Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in areas that would then have been too cold for crocodiles.