HOME

TheInfoList



OR:

The Stereospondyli are a group of extinct
temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...
amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
s that existed primarily during the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecological niche to modern
crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...
ns prior to the diversification of pseudosuchian
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avia ...
s.


Classification and anatomy

The group was first defined by Zittel (1888) on the recognition of the distinctive vertebral anatomy of the best known stereospondyls of the time, such as '' Mastodonsaurus'' and ''
Metoposaurus ''Metoposaurus'' meaning "front lizard" is an extinct genus of stereospondyl temnospondyl amphibian, known from the Late Triassic of Germany, Italy, Poland, and Portugal. https://www.app.pan.pl/archive/published/app47/app47-535.pdf This mostly a ...
''. The term 'stereospondylous' as a descriptor of vertebral anatomy was coined the following year by Fraas, referring to a vertebral position consisting largely or entirely of the intercentrum in addition to the neural arch. While the name 'Stereospondyli' is derived from the stereospondylous vertebral condition, there is a diversity of vertebral morphologies among stereospondyls, including the diplospondylous (' tupilakosaurid') condition, where the arch sits between the corresponding intercentrum and pleurocentrum, and the plagiosaurid condition, where a single large centrum ossification (identity unknown) is present, and the arch sits between subsequent vertebral positions. The concept of Stereospondyli has thus undergone repeated and frequent revisions by different workers. Defining features include a tight articulation between the parasphenoid and the pterygoid and a stapedial groove.


Evolutionary history

Stereospondyls first definitively appeared during the
early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * 01'' (Richard Müller album), 2001 * ''01'' (Son of Dave album), 2000 * ''01'' (Urban Zakapa album), 2011 * ''O1'' (Hiroyuki Sawan ...
, as represented by fragmentary remains of a rhinesuchid from the Pedra de Fogo Formation of
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. Rhinesuchids are one of the earliest groups of stereospondyls to appear in the fossil record and are predominantly a late Permian clade, with only one species, '' Broomistega putterilli,'' from the
Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is ...
of
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
. However, almost all other groups of stereospondyls are not known from any Paleozoic deposits, which remained dominated by non-stereospondyl
stereospondylomorphs Stereospondylomorpha is a clade of temnospondyls. It includes the superfamily Archegosauroidea and the more diverse group Stereospondyli. Stereospondylomorpha was first proposed by Yates and Warren (2000), who found Archegosauroidea and Stereo ...
. The taxonomically unresolved ''
Peltobatrachus pustulatus ''Peltobatrachus'' (from Greek ''pelte'', meaning shield and batrakhos, meaning frog) is an extinct genus of temnospondyl amphibian from the late Permian period of Tanzania. The sole species, ''Peltobatrachus pustulatus'', is also the sole membe ...
,'' which has historically been regarded as a stereospondyl, is also known from the late Permian of
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...
. Several more fragmentary records are known from horizons spanning the Permo-Triassic boundary in South America, such as the rhinesuchid-like '' Arachana nigra'' from Uruguay and an indeterminate mastodonsaurid from Uruguay. Following the Permo-Triassic mass extinction, stereospondyls are abundantly represented in the fossil record, particularly from Russia, South Africa, and Australia. This led Yates & Warren (2000) to propose that stereospondyls had sheltered in a high-latitude refugium that would have been somewhat shielded from the global effects of the extinction, and that they subsequently radiated from present-day Australia or Antarctica. Recent discoveries of a diverse rhinesuchid community in South America alongside non-stereospondyl stereospondylomorphs have led to an alternative hypothesis for a radiation from western Gondwana in South America. By the end of the Early Triassic, virtually all major clades of stereospondyls had appeared in the fossil record, although some were more geographically localized (e.g., lapillopsids, rhytidosteids) than those with cosmopolitan distributions (e.g., capitosauroids,
trematosauroids Trematosauroidea are an important group of Triassic temnospondyl amphibians. They flourished briefly during the Early Triassic, occurring worldwide before declining at the start of the Middle Triassic, although the group continued until the Late ...
). Stereospondyls were the latest-surviving temnospondyl group. With the diversification of crocodile-like
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avia ...
s and an
extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
at the end of the Triassic, most other temnospondyls disappeared.
Chigutisaurid Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. ...
brachyopoids persisted into the Jurassic in Asia and Australia, including '' Koolasuchus,'' the youngest known stereospondyl (late Early Cretaceous) from what is now
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. There is also sparse evidence for the persistence of some trematosauroids into the Jurassic of Asia. If the recent hypothesis that ''
Chinlestegophis ''Chinlestegophis'' is a diminutive Late Triassic stereospondyl that has been interpreted as a putative stem caecilian, a living group of legless burrowing amphibians. If ''Chinlestegophis'' is indeed both an advanced stereospondyl and a relative ...
,'' a Late Triassic stereospondyl from North America, is indeed a stem
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...
is correct, then stereospondyls would survive to the present day.


Lifestyle and ecology

Stereospondyls were particularly diverse during the Early Triassic, with small-bodied taxa such as lapillopsids and lydekkerinids that were likely more terrestrially capable present alongside larger taxa that would continue into the Middle Triassic, such as brachyopoids and trematosauroids. The vast majority of stereospondyls, particularly the large-bodied taxa, have been inferred to have been obligately aquatic based on features of the external anatomy such as a well-developed lateral line system, poorly ossified postcranial skeleton, and occasional preservation of proxies of external gills. Many taxa also reflect adaptations for an aquatic lifestyle as evidence in bone histology, which is pachyostotic in many taxa, although some studies suggest a greater terrestrial ability than historically inferred. Most of the aquatic taxa resided in freshwater environments, but some trematosauroids in particular are thought to have been
euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (''Poecilia sphenops'') which can live in fresh water, brackish water, or salt water. The green crab ('' Carcinus maenas'') is an ...
based on their preservation in marine sediments with marine organisms. While stereospondyls are often compared to modern crocodilians, the presence of multiple temnospondyls in some environments and the range of morphologies across Stereospondyli indicates that at least some clades occupied drastically different ecological niches, such as benthic ambush predators. Some groups, such as metoposaurids, are often recovered from large monotaxic
bone bed A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätt ...
s interpreted as evidence of aggregation prior to mass death.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (2015). A new species of Metoposaurus from the Late Triassic of Portugal and comments on the systematics and biogeography of metoposaurid temnospondyls. Journal of Vertebrate Paleontology. e912988., 2015:


Relationships


Phylogeny


Gallery

File:Uranocentr10 copy.jpg, '' Uranocentrodon'', a rhinesuchid File:Lyddekerina1db.jpg, '' Lydekkerina'', a lydekkerinid File:Mastodonsaurus DB.jpg, '' Mastodonsaurus'', a
capitosaur Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
File:Aphaneramma12DB.jpg, ''
Aphaneramma ''Aphaneramma'' is an extinct genus of marine temnospondyl amphibian. It lived during the Early Triassic epoch. Fossils have been found in the Mianwali Formation of Pakistan, Madagascar, the Zhitkov Formation of Russia,
'', a trematosaurid File:Pelorocephalus1DB.jpg, ''
Pelorocephalus ''Pelorocephalus'' (meaning "monstrous head" in Greek) is an extinct genus of chigutisaurid temnospondyls from the Late Triassic (Carnian) Cacheutá Formation of the Cuyo Basin and the Ischigualasto Formation of the Ischigualasto-Villa Unión ...
'', a
chigutisaurid Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. ...
File:Indobrachyops panchetensis.jpg, '' Indobrachyops'', a rhytidosteid File:Plagiosternum reconstruction.jpg, ''
Plagiosternum ''Plagiosternum'' (plae-jee-oh-ster-num, meaning "sideways breastbone") was a middle Triassic temnospondyl that is native to Spitzbergen Svalbard ( , ), also known as Spitsbergen, or Spitzbergen, is a Norwegian archipelago in the Arct ...
'', a plagiosaurid File:Metoposaurus diagnosticus kraselovi 1DB.jpg, ''
Metoposaurus ''Metoposaurus'' meaning "front lizard" is an extinct genus of stereospondyl temnospondyl amphibian, known from the Late Triassic of Germany, Italy, Poland, and Portugal. https://www.app.pan.pl/archive/published/app47/app47-535.pdf This mostly a ...
'', a metoposaurid


References

{{Taxonbar, from=Q3495411 Permian temnospondyls Triassic temnospondyls Jurassic temnospondyls Cretaceous temnospondyls