Microsauria

Microsauria ("small lizards") is an extinct order of possibly polyphyletic[1] tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls.[2][3] Recently, Microsauria has been considered paraphyletic, as several other non-microsaur lepospondyl groups such as Lysorophia seem to be nested in it.[2][4][5] Microsauria is now commonly used as a collective term for the grade of lepospondyls that were originally classified as members of Microsauria.[3]

Microbrachis

Microsauria Temporal range: Late Carboniferous-Early Permian, 318.1–270.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Microsauria diversity. (Hyloplesion (A), Pantylus (B), Pelodosotis (C) & Rhynchonkos (D))
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subclass:	†Lepospondyli
Order:	†"Microsauria" Dawson, 1863
Subgroups
See text.

The microsaurs all had short tails and small legs, but were otherwise quite varied in form. The group included lizard-like animals that were relatively well-adapted to living on dry land, burrowing forms, and others that, like the modern axolotl, retained their gills into adult life, and so presumably never left the water.[6]

Distribution

Microsaurs are known from Europe and North America.

Microsaur remains have been found from Europe and North America in Late Carboniferous and Early Permian localities. Most North American microsaurs have been found in the United States in Arizona,[7] Texas, Oklahoma, Ohio,[8] Illinois, as well as Kansas and Nebraska,[9] although remains have also been found in Nova Scotia.[10] In Europe, microsaurs are known from Germany and the Czech Republic. Possible microsaur remains have also been found from strata in the town of Vyazniki in the Vladimir Oblast of Russia.[11] These strata are Late Permian in age, near the Permo-Triassic boundary. The microsaur material at Vyazniki may be the youngest record of microsaurs, and would extend their range by around 20 million years.

Classification

Cladogram modified from Anderson (2001):[4]

Lepospondyli

Utaherpeton       Hyloplesion         Odonterpeton      Hapsidopareiontidae    Saxonerpeton       Hapsidopareion     Llistrofus          Tuditanidae    Asaphestera     Tuditanus        Ostodolepidae    Micraroter     Pelodosotis          Pantylidae    Pantylus       Stegotretus     Sparodus        Gymnarthridae    Cardiocephalus     Euryodus           Rhynchonkos       Eocaecilia (Lissamphibia)    Brachystelechidae    Batropetes       Carrolla     Quasicaecilia                         Microbrachis       Adelospondyli       Scincosaurus      Urocordylidae    Sauropleura       Urocordylus       Ctenerpeton     Ptyonius            Diplocaulidae      Batrachiderpeton     Keraterpeton         Diceratosaurus       Diploceraspis     Diplocaulus             Lysorophia     Aïstopoda                      Microsaurs

Cladogram from Ruta and Coates (2007):[5]

"Microsauria"	Odonterpeton       Hyloplesion     Microbrachis           Brachystelechidae         Tuditanidae       Hapsidopareiontidae       Ostodolepidae       Rhynchonkos     Gymnarthridae               Pantylidae       Lysorophia       Nectridea     Aïstopoda

Cladistic analysis by Pardo et al. (2017) places recumbirostran microsaurs and lysorophians as members of Amniota.[12]

References

1. https://onlinelibrary.wiley.com/doi/abs/10.1002/spp2.1316
2. Ruta, M.; Coates, M.I.; Quicke, D.L.J. (2003). "Early tetrapod relationships revisited" (PDF). Biological Reviews. 78 (2): 251–345. doi:10.1017/S1464793102006103. PMID 12803423.
3. Bolt, J.R.; Rieppel, O. (2009). "The holotype skull of Llistrofus pricei Carroll and Gaskill, 1978 (Microsauria: Hapsidopareiontidae)". Journal of Paleontology. 83 (3): 471–483. doi:10.1666/08-076.1.
4. Anderson, J.S. (2001). "The phylogenetic trunk: Maximal inclusion of taxa with missing data in an analysis of the Lepospondyli (Vertebrata, Tetrapoda)". Systematic Biology. 50 (2): 170–193. doi:10.1080/10635150119889. PMID 12116927.
5. Ruta, M.; Coates, M.I. (2007). "Dates, nodes, and character conflict: addressing the lissamphibian origin problem". Journal of Systematic Palaeontology. 5: 69–122. doi:10.1017/S1477201906002008.
6. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 55. ISBN 978-1-84028-152-1.
7. Thayer, D.W. (1985). "New Pennsylvanian lepospondyl amphibians from the Swisshelm Mountains, Arizona". Journal of Paleontology. 59 (3): 684–700.
8. Hook, R. W.; Baird, D. (1986). "The Diamond Coal Mine of Linton, Ohio, and its Pennsylvanian-Age vertebrates". Journal of Vertebrate Paleontology. 6 (2): 174–190. doi:10.1080/02724634.1986.10011609.
9. Huttenlocker, A. K.; Pardo, J. D.; Small, B. J.; Anderson, J. S. (2013). "Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography". Journal of Vertebrate Paleontology 33 (3): 540.
10. Steen, M.C. (1934). "The amphibian fauna from the South Joggins, Nova Scotia". Proceedings of the Zoological Society of London. 104 (3): 465–504. doi:10.1111/j.1096-3642.1934.tb01644.x.
11. Sennikov, A.G.; Golubev, V.K. (2006). "Vyazniki biotic assemblage of the terminal Permian" (PDF). Paleontological Journal. 40 (Suppl. 4): S475–S481. doi:10.1134/S0031030106100078.
12. Jason D. Pardo; Matt Szostakiwskyj; Per E. Ahlberg; Jason S. Anderson (2017). "Hidden morphological diversity among early tetrapods". Nature. 546 (7660): 642–645. doi:10.1038/nature22966. PMID 28636600.

External links

• Microsauria in the Paleobiology Database