The Stereospondyli are a group of extinct
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 ...
amphibian
Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s that existed primarily during the
Mesozoic
The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
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 () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
ns prior to the diversification of
pseudosuchia
Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
n
archosaur
Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...
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
''Mastodonsaurus'' (meaning "teat tooth lizard") is an extinct genus of temnospondyl amphibian from the Middle Triassic of Europe. It belongs to a Triassic group of temnospondyls called Capitosauria, characterized by their large body size, large ...
'' and ''
Metoposaurus''. 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), ''01'' (Richard Müller album), 2001
* 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011
* ''01011 ...
, as represented by fragmentary remains of a
rhinesuchid
Rhinesuchidae is a family of tetrapods that lived primarily in the Permian period. They belonged to the broad group Temnospondyli, a successful and diverse collection of semiaquatic tetrapods which modern amphibians are probably descended from. ...
from the Pedra de Fogo Formation of
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
. Rhinesuchids are one of the earliest groups of stereospondyls to appear in the fossil record and are predominantly a
late Permian
Late or LATE may refer to:
Everyday usage
* Tardy, or late, not being on time
* Late (or the late) may refer to a person who is dead
Music
* ''Late'' (The 77s album), 2000
* Late (Alvin Batiste album), 1993
* Late!, a pseudonym used by Dave Groh ...
clade, with only one species, ''
Broomistega putterilli
''Broomistega'' is an extinct genus of temnospondyl in the family Rhinesuchidae. It is known from one species, ''Broomistega putterilli'', which was renamed in 2000 from ''Lydekkerina putterilli'' Broom 1930. Fossils are known from the Early Tri ...
,'' 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 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...
of
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
. 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 Stereosp ...
. 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 member ...
,'' which has historically been regarded as a stereospondyl, is also known from the late Permian of
Tanzania
Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...
. 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 Temnospondyli, temnospondyl amphibians. They flourished briefly during the Early Triassic, occurring worldwide before declining at the start of the Middle Triassic, although the group continued ...
).
Stereospondyls were the latest-surviving temnospondyl group. With the diversification of crocodile-like
archosaur
Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...
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 fall in the diversity and abundance of multicellular organisms. It occ ...
at the end of the Triassic, most other temnospondyls disappeared.
Chigutisaurid 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 country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. 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 relati ...
,'' a Late Triassic stereospondyl from North America, is indeed a stem
caecilian
Caecilians (; ) are a group of limbless, vermiform (worm-shaped) or serpentine (snake-shaped) amphibians with small or sometimes nonexistent eyes. They mostly live hidden in soil or in streambeds, and this cryptic lifestyle renders caecilians ...
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 short-finned molly, '' Poecilia sphenops'', which can live in fresh water, brackish water, or salt water.
The green crab ('' Carcinus m ...
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 Geology, geological stratum or deposition (geology), deposit that contains bones of whatever kind. Inevitably, such deposits are Sedimentary rock, sedimentary in nature. Not a formal term, it tends to be used more to describe esp ...
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
''Uranocentrodon'' is an extinct genus of temnospondyls in the family Rhinesuchidae. Known from a skull, ''Uranocentrodon'' was a large predator with a length up to . Originally named ''Myriodon'' by van Hoepen in 1911, it was transferred to a ...
'', a rhinesuchid
Rhinesuchidae is a family of tetrapods that lived primarily in the Permian period. They belonged to the broad group Temnospondyli, a successful and diverse collection of semiaquatic tetrapods which modern amphibians are probably descended from. ...
File:Lyddekerina1db.jpg, ''Lydekkerina
''Lydekkerina'' is an extinct genus of stereospondyl temnospondyl. It is the type genus of the family Lydekkerinidae. Fossils have been collected from Early Triassic deposits in South Africa and Australia. The type species is '' L. huxleyi'', f ...
'', a lydekkerinid
File:Mastodonsaurus DB.jpg, ''Mastodonsaurus
''Mastodonsaurus'' (meaning "teat tooth lizard") is an extinct genus of temnospondyl amphibian from the Middle Triassic of Europe. It belongs to a Triassic group of temnospondyls called Capitosauria, characterized by their large body size, large ...
'', a capitosaur
File:Aphaneramma12DB.jpg, ''Aphaneramma
''Aphaneramma'' is an extinct genus of marine temnospondyl amphibian. It lived during the Early Triassic epoch, approximately 252–247 Ma ago, and had a global distribution.
Fossils have been found in the Mianwali Formation of Pakistan, Ma ...
'', a trematosaurid
File:Pelorocephalus1DB.jpg, '' Pelorocephalus'', a chigutisaurid
File:Indobrachyops panchetensis.jpg, '' Indobrachyops'', a rhytidosteid
File:Plagiosternum reconstruction.jpg, '' Plagiosternum'', a plagiosaurid
File:Metoposaurus diagnosticus kraselovi 1DB.jpg, '' Metoposaurus'', a metoposaurid
References
{{Taxonbar, from=Q3495411
Permian temnospondyls
Triassic temnospondyls
Jurassic temnospondyls
Cretaceous temnospondyls