Stereospondyli

The Stereospondyli are a group of extinct temnospondyl amphibians. 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. The family Plagiosauridae appear to have been wholly aquatic and retained their larval gills in adulthood.

Stereospondyls Temporal range: 272.95–120 Ma PreꞒ Ꞓ O S D C P T J K Pg N Possible descendant taxon Apoda (caecilians) survives to present
Life restoration of Siderops kehli, a chigutisaurid
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Temnospondyli
Clade:	†Stereospondylomorpha
Suborder:	†Stereospondyli
Subgroups
†Arachana †Capulomala †Peltobatrachus? †Lapillopsidae? †Lydekkerinidae †Rhinesuchidae †Capitosauria †Trematosauria

Stereospondyls first appeared during the Late Permian. During this time, the two major groups of stereospondyls, capitosaurians and trematosaurians, appeared. Stereospondyls were relatively uncommon in the Paleozoic, outnumbered by the more diverse euskelians. During this time, they were endemic to Gondwana. Many early groups of temnospondyls became 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 archosaurs 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 cool for crocodiles. Some groups, such as the Metoposaurus, are often associated to mass mortality and bone beds.[1] Chinlestegophis, a putative Triassic stereospondyl considered to be related to metoposauroids such as Rileymillerus, has been noted to share many features with caecilians, a living group of legless burrowing amphibians. If Chinlestegophis is indeed both an advanced stereospondyl and a relative of caecilians, this means that stereospondyls (in the form of caecilians) survived to the present day.[2]

Classification

Phylogeny

	Peltobatrachidae
	Lapillopsidae       Rhinesuchidae       Lydekkerinidae       Capitosauria   Mastodonsauroidea     Trematosauria Trematosauroidea   Benthosuchus     Thoosuchidae     Trematosauridae       Metoposauroidea   Latiscopidae     Metoposauridae     Plagiosauroidea   Plagiosauridae     Laideriidae       Rhytidosteoidea   Inobrachyopidae     Rhytidosteidae       Brachyopoidea   Brachyopidae     Chigutisauridae

Gallery

• 
  Uranocentrodon, a rhinesuchid
• 
  Lydekkerina, a lydekkerinid
• 
  Mastodonsaurus, a capitosaur
• 
  Aphaneramma, a trematosaurid
• 
  Pelorocephalus, a chigutisaurid
• 
  Indobrachyops, a rhytidosteid
• 
  Plagiosternum, a plagiosaurid
• 
  Metoposaurus, a metoposaurid

References

1. 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:
2. Pardo, Jason D.; Small, Bryan J.; Huttenlocker, Adam K. (2017-07-03). "Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia". Proceedings of the National Academy of Sciences. 114 (27): E5389–E5395. doi:10.1073/pnas.1706752114. ISSN 0027-8424. PMC 5502650. PMID 28630337.

• Yates, A. M. & Warren, A. A. (2000), The phylogeny of the 'higher' temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyli. Zoological Journal of the Linnean Society 128: 77-121.