Pelycosaur

Pelycosaurs Temporal range:Pennsylvanian-Capitanian,308–260.4MaDescendant taxonTherapsidasurvives to present. PreꞒ Ꞓ O S D C P T J K Pg N
	Mounted skeleton ofDimetrodon milleri,Harvard Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Tetrapoda
Clade:	Reptiliomorpha
Clade:	Amniota
Clade:	Synapsida
Informal group:	†Pelycosauria; Cope,1878
Groups included
	†Caseidae; †Eothyrididae; †Varanopidae?; †Ophiacodontidae; †Edaphosauridae; †Palaeohatteriidae; †Sphenacodontidae;
Cladisticallyincluded but traditionally excluded taxa
	Therapsida;

Pelycosaur(/ˈpɛlɪkəˌsɔːr/PEL-ih-kə-sor)^[1]is an older term forbasalor primitive LatePaleozoic synapsids,excluding thetherapsidsand their descendants. Previously, the termmammal-like reptilehad been used,^[2]and pelycosaur was considered anorder,but this is now thought to be incorrect and outdated.

Because it excludes the advanced synapsid groupTherapsida,the term isparaphyleticand contrary to modern formal naming practice.^[3]^[4]Thus the namepelycosaurs,similar to the termmammal-like reptiles,had fallen out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature.^[5]^[6]The termsstem mammals,protomammals,andbasalorprimitive synapsidsare instead used where needed.

Etymology

The modern word was created from Greekpélyxmeaning 'basin' andsaûrosmeaning 'lizard'.^[7]The termpelycosaurhas been fairly well abandoned by paleontologists because it no longer matches the features that distinguish a clade.^[6]

Pelycosauria is aparaphyletictaxon because it excludes thetherapsids.For that reason, the term is sometimes avoided by proponents of a strict cladistic approach.Eupelycosauriais used to designate the clade that includes most pelycosaurs, along with the Therapsida and Mammalia. In contrast to "pelycosaurs", Eupelycosauria is a propermonophyleticgroup.Caseasauriais a pelycosaur side-branch, or clade, that did not leave any descendants.^{[citation needed]}

Evolutionary history

Comparison of "pelycosaurian" skulls: 1 sphenacodont, 2 ophiacodont, 3 caseid. Thequadratojugaleis green,squamosaleis red,jugaleis blue.

The pelycosaurs appear to have been a group of synapsids that have direct ancestral links with themammals,having differentiated teeth and a developing hard palate. The pelycosaurs appeared during theLate Carboniferousand reached their apex in theearly part of the Permian,remaining the dominant land animals for some 40 million years. A few continued into theCapitanian,but they experienced a sharp decline in diversity in the lateKungurian.^[8]They were succeeded by thetherapsids.

Description

Cotylorhynchus(background),OphiacodonandVaranops

Some species were quite large, growing to a length of 3 metres (10 ft) or more, although most species were much smaller. Well-known pelycosaurs include thegeneraDimetrodon,Sphenacodon,Edaphosaurus,andOphiacodon.^[9]

Pelycosaur fossils have been found mainly inEuropeandNorth America,although some small, late-surviving forms are known fromRussiaandSouth Africa.

Unlikelepidosaurianreptiles, pelycosaurs might have lacked reptilian epidermalscales.^{[disputed–discuss]}Fossil evidence from somevaranopidsshows that parts of the skin were covered in rows ofosteoderms,presumably overlain by hornyscutes.^[5]The belly was covered in rectangular scutes, looking like those present incrocodiles.^[10]Parts of the skinnotcovered in scutes might have had naked, glandular skin like that found in some mammals. Dermal scutes are also found in a diverse number of extant mammals with conservative body types, such as in the tails of somerodents,sengis,moonrats,theopossums,and othermarsupials,and as regular dermal armour with underlying bone in thearmadillo.

At least two pelycosaurcladesindependently evolved a tallsail,consisting of elongated vertebral spines: theedaphosauridsand thesphenacodontids.In life, this may have been covered by skin, and likely functioned as athermoregulatorydevice^[11]or as amating display.

Taxonomy

Eothyris

Dimetrodon– a sphenacodontid

In phylogenetic nomenclature, "Pelycosauria" is not used formally, since it does not constitute a group ofallorganisms descended from some common ancestor (aclade), because the group specifically excludes the therapsids which are descended from pelycosaurs. Instead, it represents a paraphyletic "grade" of basal synapsids leading up to the clade Therapsida.^[12]

In 1940, the group was reviewed in detail, and every species known at the time described, with many illustrated, in an important monograph byAlfred Sherwood RomerandLlewellyn Price.^[13]

In traditional classification, the order Pelycosauria isparaphyleticin that thetherapsids(the "higher" synapsids) have emerged from them. That means Pelycosauria is a grouping of animals that does not contain all descendants of its common ancestor, as is often required byphylogenetic nomenclature.Inevolutionary taxonomy,Therapsida is a separated order from Pelycosauria, andmammals(having evolved from therapsids) are separated from both as their own class. This use has not been recommended by a majority of systematists since the 1990s,^[6]but several paleontologists nevertheless continue using this word.^[14]^[12]

The following classification was presented by Benton in 2004.^[15]

Order Pelycosauria*
- SuborderCaseasauria
  - FamilyEothyrididae
  - FamilyCaseidae
- SuborderEupelycosauria
  - FamilyVaranopidae
  - FamilyOphiacodontidae
  - FamilyEdaphosauridae
  - InfraorderSphenacodontia
    - FamilySphenacodontidae
OrderTherapsida

Notes

^Cope, E. D. (1878)."Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas".Proceedings of the American Philosophical Society.17(101): 505–530.JSTOR 982652.
^Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company, New York ISBN 0-7167-1822-7
^Hennig, Willi (1981).Insect phylogeny.Chichester [England]: J. Wiley. pp. xi + 514.ISBN 0471278483.
^D. W. Dilkes, R. R. Reisz (1996)."First Record of a Basal Synapsid ('Mammal-Like Reptile') in Gondwana".Proceedings of the Royal Society B.263(1374): 1165–1170.doi:10.1098/rspb.1996.0170.
^^a ^bBotha-Brink, J.; Modesto, S.P. (2007)."A mixed-age classed 'pelycosaur' aggregation from South Africa: Earliest evidence of parental care in amniotes?".Proceedings of the Royal Society B.274(1627): 2829–2834.doi:10.1098/rspb.2007.0803.PMC2288685.PMID 17848370.
^^a ^b ^cLaurin, Michel (2010).How Vertebrates Left the Water.Berkeley, CA: University of California Press. pp. xv + 199.ISBN 978-0-520-26647-6.
^Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951).The dinosaur book: the ruling reptiles and their relatives.New York: McGraw-Hill. p. 152.
^Didier, Gilles; Laurin, Michel (2021)."Distributions of extinction times from fossil ages and tree topologies: the example of some mid-Permian synapsid extinctions".PeerJ.9(e12577): e12577.doi:10.7717/peerj.12577.PMC8667717.PMID 34966586.
^Cowen, Richard (2013).History of Life.John Wiley & Sons. pp. 91–92.ISBN 978-1-11851-093-3.
^Carroll, R.L. (1969). "Problems of the origin of reptiles".Biological Reviews.44(3): 393–432.doi:10.1111/j.1469-185X.1969.tb01218.x.S2CID 84302993.
^Tracy, C.R.;Turner, J.S.;Huey, R.B.(1986). "A biophysical analysis of possible thermoregulatoryadaptations in pelycosaurs". In MacLean, P.D.; Roth, J.J.; Roth, E.C.; Hotton, N. (eds.).Ecology and Biology of Mammal-Like Reptiles.Washington, DC: Smithsonian Press. pp. 195–205.
^^a ^bBrocklehurst, Neil; Fröbisch, Jörg (2018). "A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids".Journal of Vertebrate Paleontology.35(8): e1508026.doi:10.1080/02724634.2018.1508026.S2CID 91487577.
^Romer, A.S.;Price, L.I.(1940). "Review of the Pelycosauria".28: Review of the Pelycosauria.Geological Society of America Special Papers. Vol. 28. pp. 1–538.doi:10.1130/SPE28-p1.
^Amson, Eli; Laurin, Michel (2011)."On the affinities of Tetraceratops insignis, an Early Permian synapsid".Acta Palaeontologica Polonica.56(2): 301–312.doi:10.4202/app.2010.0063.S2CID 56425905.
^Benton, Michael J. (2004).Vertebrate palaeontology(3rd ed.). Oxford: Blackwell Science.ISBN 978-0-632-05637-8.

References

Reisz, R.R.(1986).Handbuch der Paläoherpetologie[Encyclopedia of Paleoherpetology]. Verlag Dr. Friedrich Pfeil. Part 17A Pelycosauria.ISBN 3-89937-032-5.

External links

"Introduction to the Pelycosaurs".UCMP.
"Synapsida - Pelycosauria".Palaeos.Archived fromthe originalon 2006-03-13.

[Co78-1] Cope, E. D. (1878)."Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas".Proceedings of the American Philosophical Society.17(101): 505–530.JSTOR 982652.

[2] Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company, New York ISBN 0-7167-1822-7

[Hennig_81-3] Hennig, Willi (1981).Insect phylogeny.Chichester [England]: J. Wiley. pp. xi + 514.ISBN 0471278483.

[Dilkes1996-4] D. W. Dilkes, R. R. Reisz (1996)."First Record of a Basal Synapsid ('Mammal-Like Reptile') in Gondwana".Proceedings of the Royal Society B.263(1374): 1165–1170.doi:10.1098/rspb.1996.0170.

[brink&modesto2007-5] Botha-Brink, J.; Modesto, S.P. (2007)."A mixed-age classed 'pelycosaur' aggregation from South Africa: Earliest evidence of parental care in amniotes?".Proceedings of the Royal Society B.274(1627): 2829–2834.doi:10.1098/rspb.2007.0803.PMC2288685.PMID 17848370.

[La10-6] Laurin, Michel (2010).How Vertebrates Left the Water.Berkeley, CA: University of California Press. pp. xv + 199.ISBN 978-0-520-26647-6.

[7] Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951).The dinosaur book: the ruling reptiles and their relatives.New York: McGraw-Hill. p. 152.

[DiLa21-8] Didier, Gilles; Laurin, Michel (2021)."Distributions of extinction times from fossil ages and tree topologies: the example of some mid-Permian synapsid extinctions".PeerJ.9(e12577): e12577.doi:10.7717/peerj.12577.PMC8667717.PMID 34966586.

[Cowen2013-9] Cowen, Richard (2013).History of Life.John Wiley & Sons. pp. 91–92.ISBN 978-1-11851-093-3.

[caroll1969-10] Carroll, R.L. (1969). "Problems of the origin of reptiles".Biological Reviews.44(3): 393–432.doi:10.1111/j.1469-185X.1969.tb01218.x.S2CID 84302993.

[11] Tracy, C.R.;Turner, J.S.;Huey, R.B.(1986). "A biophysical analysis of possible thermoregulatoryadaptations in pelycosaurs". In MacLean, P.D.; Roth, J.J.; Roth, E.C.; Hotton, N. (eds.).Ecology and Biology of Mammal-Like Reptiles.Washington, DC: Smithsonian Press. pp. 195–205.

[BrFr18-12] Brocklehurst, Neil; Fröbisch, Jörg (2018). "A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids".Journal of Vertebrate Paleontology.35(8): e1508026.doi:10.1080/02724634.2018.1508026.S2CID 91487577.

[RomerPrice1940-13] Romer, A.S.;Price, L.I.(1940). "Review of the Pelycosauria".28: Review of the Pelycosauria.Geological Society of America Special Papers. Vol. 28. pp. 1–538.doi:10.1130/SPE28-p1.

[Amson&Laurin11-14] Amson, Eli; Laurin, Michel (2011)."On the affinities of Tetraceratops insignis, an Early Permian synapsid".Acta Palaeontologica Polonica.56(2): 301–312.doi:10.4202/app.2010.0063.S2CID 56425905.

[Benton2004-15] Benton, Michael J. (2004).Vertebrate palaeontology(3rd ed.). Oxford: Blackwell Science.ISBN 978-0-632-05637-8.

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