Lepospondyli

Source: Wikipedia, the free encyclopedia.

Lepospondyls
Temporal range:
350–255 
Ma
Late Permian[2]
Diplocaulus, a diplocaulid "nectridean"
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Tetrapodomorpha
Clade: Stegocephali
Subclass: †Lepospondyli
Zittel, 1888
Groups

Lissamphibia?
†Westlothiana?[3]
†Adelospondyli?
†

Aïstopoda
?
†Lysorophia
†"Microsauria"
†"Nectridea"

Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the

temnospondyl
amphibians that coexisted with them in the Paleozoic. Lepospondyli was named in 1888 by
polyphyletic, with aïstopods being primitive stem-tetrapods, while recumbirostran microsaurs are primitive reptiles.[10]

Description

All lepospondyls are characterised by having simple, spool-shaped

ossify from cartilage, but rather grew as bony cylinders around the notochord. In addition, the upper portion of the vertebra, the neural arch, is usually fused to the centrum (the main body of the vertebra).[11]

Classification

The position of the Lepospondyli within the Tetrapoda is uncertain because the earliest lepospondyls were already highly specialized when they first appeared in the fossil record. Some lepospondyls were once thought to be related or perhaps ancestral to modern

stem tetrapod groups and others more closely related to modern amphibians or reptiles.[14]
Early phylogenetic analyses conducted in the 1980s and 1990s often maintained the idea that lepospondyls were paraphyletic, with nectrideans close to colosteids and microsaurs close to temnospondyls, which were considered to be ancestral to modern amphibians.

However, a 1995 paper by Robert Carroll argued that lepospondyls were actually a monophyletic group closer to reptiles. Carroll considered them closer to reptiles than the seymouriamorphs, but not as close as the diadectomorphs.[15] Many phylogenetic analyses since Carroll (1995) agreed with his interpretation, including Laurin & Reisz (1997),[16] Anderson (2001),[17] and Ruta et al. (2003).[9] A few have still considered lepospondyls ancestral to amphibians, but came to this conclusion without changing the position of lepospondyls compared to seymouriamorphs and diadectomorphs.[8]

Lepospondyl and tetrapod classification is still controversial, and even recent studies have had doubts about lepospondyl monophyly. For example, a 2007 paper has suggested that adelospondyls are stem-tetrapods close to colosteids[3] and a 2017 paper on Lethiscus has Aïstopoda in the tetrapod stem based on their primitive braincase.[18] These studies differ in the internal and external relationships of the remaining lepospondyl taxa. The former places the remaining lepospondyls into a single clade along the amniote stem. The latter does not treat the relationships of nectrideans or adelospondyls, but finds microsaurs to be early amniotes, and places lysorophians within microsaurs.

Interrelationships

Five main groups of lepospondyls are often recognized:

monophyletic group, it has been considered an evolutionary grade of basal ("primitive") lepospondyls, although there is growing consensus that a large subset of fossorially-adapted microsaurs, the Recumbirostra, is monophyletic. Lysorophia may belong within the Recumbirostran clade, distinct from other derived lepospondyls. Nectridea may also be paraphyletic, consisting of a range of more anatomically-specialized lepospondyls.[19] The name Holospondyli has been proposed for a clade including aïstopods, and nectrideans, and possibly adelospondyls, although not all recent phylogenetic analyses support the grouping. The following cladogram, simplified, is after an analysis of tetrapods and stem-tetrapods presented by Ruta et al. in 2003:[9]

 Lepospondyli 

Batropetes fritschi

Tuditanus punctulatus

Pantylus cordatus

Stegotretus agyrus

Asaphestera intermedia

Saxonerpeton geinitzi

Hapsidopareion lepton

Micraroter erythrogeios

Pelodosotis elongatum

Rhynchonkos stovalli

Cardiocephalus sternbergi

Euryodus primus

Microbrachis pelikani

Hyloplesion longicostatum

Odonterpeton triangulare

 Lysorophia 
 
Acherontiscidae
 

Acherontiscus caledoniae

 Adelospondyli 

Adelospondylus watsoni

Adelogyrinus simorhynchus

Dolichopareias disjectus

 Holospondyli 

Scincosaurus crassus

Keraterpeton galvani

Batrachiderpeton reticulatum

Diceratosaurus brevirostris

Diplocaulus magnicornis

Diploceraspis burkei

Ptyonius marshii

Sauropleura spp.

Urocordylus wandesfordii

 Aistopoda 

Lethiscus stocki

Oestocephalus amphiuminum

Phlegethontia linearis

Position within Tetrapoda

The "lepospondyl hypothesis" of modern amphibian origins proposes that lissamphibians are

phylogenetic analyses continue to find support for the lepospondyl hypothesis. The analysis by Vallin and Laurin (2004) found lissamphibians to be most closely related to lysorophians, followed by microsaurs. Pawley (2006) also found lysorophians to be the closest relatives of lissamphibians, but found aïstopods and adelogyrinids rather than microsaurs to be the second most closely related groups. Marjanović (2010) found holospondyls to be the most closely related group to lissamphibians, followed by lysorophians. Under this hypothesis, lepospondyls would be crown tetrapods and temnospondyls would be stem tetrapods.[8]

Below is a cladogram from Ruta et al. (2003) that supports the "temnospondyl hypothesis", showing the position of Lepospondyli within crown group Tetrapoda:[9]

 
Tetrapoda
 

Lissamphibia + Temnospondyli

Caerorhachis bairdi

 
Eoherpetontidae
 

Eoherpeton watsoni

 Embolomeri 

Proterogyrinus scheelei

Archeria crassidisca

Pholiderpeton scutigerum

Anthracosaurus russelli

Eogyrinus
)

 Gephyrostegidae 

Bruktererpeton fiebigi

Gephyrostegus bohemicus

Solenodonsaurus janenschi

 Seymouriamorpha 

Kotlassia prima

Discosauriscus austriacus

Seymouria spp.

Lepospondyli

Westlothiana lizziae

Amniota

 Diadectomorpha 

Silvadectes
)

Limnoscelis paludis

Gallery

References

  1. S2CID 84460890
    .
  2. ^ Anderson, J. S.; Kissel, R. A. (2002). "Lepospondyl diversity in the Early Permian and Late Pennsylvanian". Journal of Vertebrate Paleontology. 22 (3): 32A.
  3. ^
    S2CID 86479890
    .
  4. S2CID 128605530
    .
  5. ^ Carroll, R. L. (1988) Vertebrate Paleontology and Evolution, WH Freeman & Co.
  6. S2CID 26700362
    .
  7. S2CID 12023942
    .
  8. ^
    S2CID 67823991
    .
  9. ^
    S2CID 31298396
    .
  10. ^ Jason D. Pardo, Matt Szostakiwskyj, Per E. Ahlberg & Jason S. Anderson (2017) Hidden morphological diversity among early tetrapods. Nature (advance online publication) doi:10.1038/nature22966>
  11. ^ a b Colbert 1969
  12. ^ Romer 1966
  13. ^ Carroll 1988
  14. ^ Benton 2000
  15. ^ Carroll, Robert L. (1995). "Problems of the phylogenetic analysis of Paleozoic choanates". Bulletin du Muséum National d'Histoire Naturelle, Section C. Series 4. 17 (1–4): 389–445.
  16. ^ Laurin, Michel; Reisz, Robert R. (1997). "Chapter 2: A new perspective on tetrapod phylogeny". In Sumida, S.; Martin, K. (eds.). Amniote origins—Completing the transition to land. London: Academic Press. pp. 9–59.
  17. PMID 12116927
    .
  18. S2CID 2478132
    .
  19. S2CID 85114894
    .
  20. doi:10.1111/j.1096-3642.2010.00683.x
    .

External links

Wikimedia Commons has media related to Lepospondyli.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Lepospondyli&oldid=1216636697"