Editing Therapsida

{{Short description|Clade of tetrapods including mammals}}
{{Distinguish|Synapsid{{!}}Theropsida}}
{{Use dmy dates|date=November 2014}}
{{Automatic taxobox
| fossil_range = {{fossil range|272.5|0|[[Cisuralian]]–[[Holocene]] 279.5–0 Ma||PS=(Range includes [[mammal]]s)}}
| image = Therapsida 3.jpg
| image_caption = From top to bottom and left to right, several examples of non-mammalian therapsids: ''[[Biarmosuchus]]'' ([[Biarmosuchia]]), ''[[Moschops]]'' ([[Dinocephalia]]), ''[[Lystrosaurus]]'' ([[Anomodont]]ia), ''[[Inostrancevia]]'' ([[Gorgonopsia]]), a [[lycosuchid]] ([[Therocephalia]])  and ''[[Chiniquodon]]'' ([[Cynodont]]ia)
| image_upright = 1.2
| display_parents = 3
| taxon = Therapsida
| authority = [[Robert Broom|Broom]], 1905<ref name="Broom1905">{{cite journal|last=Broom|first=R.|author-link=Robert Broom|year=1905|title=On the use of the term Anomodontia|journal=Records of the Albany Museum|volume=1|issue=4|pages=266–269|url=https://www.biodiversitylibrary.org/page/7000255#page/292/mode/1up}}</ref>
| subdivision_ranks = [[Clade]]s
| subdivision = *{{extinct}}''[[Raranimus]]''
*†[[Biarmosuchia]]
*†[[Dinocephalia]]
*†[[Anomodont]]ia
**Various extinct taxa
**†[[Dicynodont]]ia
*[[Theriodontia]]
**†[[Gorgonopsia]]
**[[Eutheriodontia]]
***†[[Therocephalia]]
***[[Cynodont]]ia
****Various extinct taxa
****[[Mammal]]ia
}}

'''Therapsida'''{{efn|[[Greek language|Greek]]: 'beast-arch'}} is a clade comprising a major group of [[eupelycosauria]]n [[synapsid]]s that includes [[mammal]]s and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, resulting in a more "standing" [[quadrupedal]] posture, as opposed to the lower sprawling posture of many [[reptile]]s and [[amphibian]]s.

Therapsids evolved from earlier synapsids commonly called "[[pelycosaur]]s", specifically within the [[Sphenacodontia]], more than 279.5 million years ago. They replaced the pelycosaurs as the dominant large land animals in the [[Guadalupian]] through to the Early Triassic. In the aftermath of the [[Permian–Triassic extinction event]], therapsids declined in relative importance to the rapidly diversifying [[archosaurian]] [[sauropsid]]s ([[pseudosuchia]]ns, [[dinosaur]]s and [[pterosaur]]s, etc.) during the Middle Triassic.

The therapsids include the [[cynodont]]s, the group that gave rise to mammals ([[Mammaliaformes]]) in the Late Triassic around 225 million years ago, the only therapsid clade that survived beyond the end of the [[Triassic]]. The only other group of therapsids to have survived into the [[Late Triassic]], the [[dicynodont]]s, became extinct towards the end of the period. The last surviving group of non-mammaliaform cynodonts were the [[Tritylodontidae]], which became extinct during the [[Early Cretaceous]].

==Characteristics==
[[Image:Pristeroognathus DB.jpg|thumb|left|Illustration of ''[[Alopecognathus]]'', an early [[therocephalia]]n therapsid]]

===Jaw and teeth===
Therapsids' [[temporal fenestra]]e were larger than those of the pelycosaurs. The jaws of some therapsids were more complex and powerful, and the [[teeth]] were differentiated into frontal [[incisor]]s for nipping, great lateral [[canine tooth|canines]] for puncturing and tearing, and [[molar (tooth)|molars]] for shearing and chopping food.
===Posture===

Therapsid legs were positioned more vertically beneath their bodies than were the sprawling legs of [[reptile]]s and pelycosaurs. Also compared to these groups, the feet were more symmetrical, with the first and last toes short and the middle toes long, an indication that the foot's [[Axis (anatomy)|axis]] was placed parallel to that of the animal, not sprawling out sideways. This orientation would have given a more [[mammal]]-like gait than the [[lizard]]-like gait of the pelycosaurs.<ref>{{cite book|last=Carroll|author-link=Robert L. Carroll|first=R. L.|title=Vertebrate Paleontology and Evolution|year=1988|publisher=W. H. Freeman and Company|location=New York|isbn=978-0-7167-1822-2|pages=[https://archive.org/details/vertebratepaleon0000carr/page/698 698]|title-link=Vertebrate Paleontology and Evolution}}</ref>

===Physiology===

The physiology of therapsids is poorly understood. Most Permian therapsids had a pineal foramen, indicating that they had a [[parietal eye]] like many modern reptiles and amphibians. The parietal eye serves an important role in thermoregulation and the [[circadian rhythm]] of ectotherms, but is absent in modern mammals, which are [[endothermic]].<ref name=Benoit2016B/> Near the end of the Permian, dicynodonts, [[therocephalia]]ns and cynodonts show [[parallel evolution|parallel]] trends towards loss of the pineal foramen, and the foramen is completely absent in [[probainognathian cynodont]]s. Evidence from oxygen isotopes, which are correlated with body temperature, suggests that most Permian therapsids were ectotherms and that endothermy evolved convergently in dicynodonts and cynodonts near the end of the Permian.<ref name=Rey2017/> In contrast, evidence from histology suggests that endothermy is shared across Therapsida,<ref name=FraureBrac2020/> whereas estimates of blood flow rate and lifespan in the mammaliaform ''[[Morganucodon]]'' suggest that even early mammaliaforms had reptile-like metabolic rates.<ref name=Newham2020/> Evidence for respiratory turbinates, which have been hypothesized to be indicative of endothermy, was reported in the therocephalian ''[[Glanosuchus]]'', but subsequent study showed that the apparent attachment sites for turbinates may simply be the result of distortion of the skull.<ref name=Hopson2012/>

===Integument===

The evolution of integument in therapsids is poorly known, and there are few fossils that provide direct evidence for the presence or absence of fur. The most basal synapsids with unambiguous direct evidence of fur are [[docodonts]], which are mammaliaforms very closely related to crown-group mammals. Two "mummified" juvenile specimens of the dicynodont ''[[Lystrosaurus murrayi]]'' preserve skin impressions; the skin is hairless, leathery, and dimpled, somewhat comparable to elephant skin.<ref>{{Cite journal |last1=Smith |first1=Roger M.H. |last2=Botha |first2=Jennifer |last3=Viglietti |first3=Pia A. |date=15 October 2022 |title=Taphonomy of drought afflicted tetrapods in the Early Triassic Karoo Basin, South Africa |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018222003777 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=604 |pages=111207 |doi=10.1016/j.palaeo.2022.111207|bibcode=2022PPP...60411207S |url-access=subscription }}</ref><ref>{{Cite web |last=Timmons |first=Jeanne |date=2022-09-20 |title=These Fossil Mummies Reveal a Brutal World Long Before T. Rex Lived |url=https://gizmodo.com/these-fossil-mummies-reveal-a-brutal-world-long-before-1849558556 |access-date=2024-07-25 |website=Gizmodo |language=en-US}}</ref> Fossilized facial skin from the dinocephalian ''[[Estemmenosuchus]]'' has been described as showing that the skin was glandular and lacked both scales and hair.<ref name=Chudinov1968/>

[[Coprolite]]s containing what appear to be hairs have been found from the [[Late Permian]].<ref name=Smith2011/><ref name=Bajdek2016/> Though the source of these hairs is not known with certainty, they may suggest that hair was present in at least some Permian therapsids.

The closure of the pineal foramen in probainognathian cynodonts may indicate a mutation in the regulatory gene Msx2, which is involved in both the closure of the skull roof and the maintenance of hair follicles in mice.<ref name=Benoit2016A/> This suggests that hair may have first evolved in probainognathians, though it does not entirely rule out an earlier origin of fur.<ref name=Benoit2016A/>

Whiskers probably evolved in probainognathian cynodonts.<ref name=Benoit2016A/><ref name=Benoit2020/> Some studies had inferred an earlier origin for whiskers based on the presence of foramina on the snout of therocephalians and early cynodonts, but the arrangement of foramina in these taxa actually closely resembles lizards,<ref name=Estes1961/> which would make the presence of mammal-like whiskers unlikely.<ref name=Benoit2020/>

==Evolutionary history==
{{See also|Evolution of mammals}}
[[Image:Raranimus dashankouensis.jpg|thumb|left|200 px|Holotype skull of ''[[Raranimus dashankouensis]]'', the most basal-known therapsid<ref name="LRL09">{{cite journal |last1=Liu |first1=Jun |last2=Rubidge |first2=Bruce |last3=Li |first3=Jinling |name-list-style=and |year=2009 |title=New basal synapsid supports Laurasian origin for therapsids |url=http://www.app.pan.pl/archive/published/app54/app20080071.pdf |journal=Acta Palaeontologica Polonica |volume=54 |issue=3 |pages=393–400 |doi=10.4202/app.2008.0071 |access-date=2009-09-25 |doi-access=free}}</ref>]]
Therapsids [[evolution|evolved]] from a group of pelycosaurs called [[Sphenacodontia|sphenacodonts]].<ref>[http://tolweb.org/accessory/Synapsid_Classification_&_Apomorphies?acc_id=466 Synapsid Classification & Apomorphies<!-- Bot generated title -->]</ref><ref>{{cite book |last1=Huttenlocker |first1=Adam K. |title=Forerunners of Mammals: Radiation, Histology, Biology |last2=Rega |first2=Elizabeth |publisher=[[Indiana University Press]] |year=2012 |isbn=978-0253005335 |editor1-last=Chinsamy-Turan |editor1-first=Anusuya |pages=90–119 |chapter=Chapter 4. The Paleobiology and Bone Microstructure of Pelycosauriangrade Synapsids |chapter-url=https://books.google.com/books?id=cp26-CA2CDUC&pg=PA91 |name-list-style=and}}</ref> Therapsids became the dominant land animals in the Middle [[Permian]], displacing the pelycosaurs. Therapsida consists of four major [[clades]]: the [[dinocephalia]]ns, the herbivorous [[anomodont]]s, the carnivorous [[biarmosuchia]]ns, and the mostly carnivorous [[theriodont]]s. After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian ([[Guadalupian]]) but the anomodont [[dicynodont]]s as well as the theriodont [[gorgonopsia]]ns and therocephalians flourished, being joined at the very end of the Permian by the first of the [[cynodont]]s.
[[File:Euchambersia DB.jpg|thumb|200px|Restoration of ''[[Euchambersia]]'' with [[dicynodont]] prey. Note that this [[South Africa]]n [[therocephalia]]n is suspected to be the oldest-known [[venom]]ous [[tetrapod]].<ref name="2017ct">{{cite journal |last1=Benoit |first1=Julien |last2=Norton |first2=Luke A. |last3=Manger |first3=Paul R. |last4=Rubidge |first4=Bruce S. |name-list-style=and |date=2017 |editor-last=Claessens |editor-first=Leon |title=Reappraisal of the envenoming capacity of ''Euchambersia mirabilis'' (Therapsida, Therocephalia) using μCT-scanning techniques |journal=PLOS ONE |volume=12 |issue=2 |page=e0172047 |bibcode=2017PLoSO..1272047B |doi=10.1371/journal.pone.0172047 |pmc=5302418 |pmid=28187210 |doi-access=free}}</ref>]] 
Like all land animals, the therapsids were seriously affected by the [[Permian–Triassic extinction event]], with the very successful gorgonopsians and the biarmosuchians dying out altogether and the remaining groups—dicynodonts, therocephalians and cynodonts—reduced to a handful of species each by the earliest [[Triassic]]. Surviving dicynodonts were represented by two families of [[disaster taxa]] ([[Lystrosauridae]] and [[Myosauridae]]), the scarcely known ''[[Kombuisia]]'', and a single group of large stocky [[herbivore]]s, the [[Kannemeyeriiformes]], which were the only dicynodont lineage to thrive during the Triassic.<ref>{{Cite journal |last1=Kammerer |first1=Christian F. |last2=Fröbisch |first2=Jörg |last3=Angielczyk |first3=Kenneth D. |date=2013-05-31 |editor-last=Farke |editor-first=Andrew A. |title=On the Validity and Phylogenetic Position of Eubrachiosaurus browni, a Kannemeyeriiform Dicynodont (Anomodontia) from Triassic North America |journal=PLOS ONE |language=en |volume=8 |issue=5 |pages=e64203 |doi=10.1371/journal.pone.0064203 |doi-access=free |issn=1932-6203 |pmc=3669350 |pmid=23741307|bibcode=2013PLoSO...864203K }}</ref> They and the medium-sized cynodonts (including both carnivorous and herbivorous forms) flourished worldwide throughout the Early and Middle Triassic. They disappear from the fossil record across much of [[Pangea]] at the end of the [[Carnian]] (Late Triassic), although they continued for some time longer in the wet equatorial band and the south.{{cn|date=August 2024}}

Some exceptions were the still further derived [[eucynodonts]].<ref>{{Cite journal |last=Padian |first=Kevin |author-link=Kevin Padian |date=2013-09-04 |title=A Review of "Forerunners of Mammals: Radiation, Histology, Biology" |journal=[[Journal of Vertebrate Paleontology]] |volume=33 |issue=5 |pages=1250–1251 |doi=10.1080/02724634.2013.763814 |bibcode=2013JVPal..33.1250P |issn=0272-4634}}</ref> At least three groups of them survived. They all appeared in the [[Late Triassic]] period. The extremely mammal-like family, [[Tritylodontidae]], survived into the Early [[Cretaceous]]. Another extremely mammal-like family, [[Tritheledontidae]], are unknown later than the Early [[Jurassic]]. [[Mammaliaformes]] was the third group, including ''Morganucodon'' and similar animals. Some taxonomists refer to these animals as "mammals", though most limit the term to the mammalian [[crown group]].
[[File:Bonacynodon witout visible ears.png|thumb|200 px|Reconstruction of ''[[Bonacynodon schultzi]]'', a probainognathian [[cynodont]] related to the ancestors of [[mammal]]s<ref name="SciAm">{{cite news |last=Geggel |first=L. |title=Meet the Ancient Reptile that Gave Rise to Mammals |date=2016 |url=https://www.scientificamerican.com/article/meet-the-ancient-reptile-that-gave-rise-to-mammals/ |work=Scientific American |language=en}}</ref>]]
The non-eucynodont cynodonts survived the Permian–Triassic extinction; ''[[Thrinaxodon]]'', ''[[Galesaurus]]'' and ''[[Platycraniellus]]'' are known from the [[Early Triassic]]. By the [[Middle Triassic]], however, only the eucynodonts remained.

The therocephalians, relatives of the cynodonts, managed to survive the Permian–Triassic extinction and continued to diversify through the Early Triassic period. Approaching the end of the period, however, the therocephalians were in decline to eventual extinction, likely outcompeted by the rapidly diversifying Saurian lineage of [[diapsid]]s, equipped with sophisticated respiratory systems better suited to the very hot, dry and oxygen-poor world of the End-Triassic.

Dicynodonts were among the most successful groups of therapsids during the Late Permian; they survived through to near the end of the Triassic.

Mammals are the only living therapsids. The mammalian crown group, which evolved in the [[Early Jurassic]] period, radiated from a group of mammaliaforms that included the docodonts. The mammaliaforms themselves evolved from [[probainognathia]]ns, a lineage of the eucynodont suborder.

==Classification==
{{cladogram|caption=The Hopson and Barghausen paradigm for therapsid relationships|clades=
{{clade
|label1='''Therapsida'''
|1 = {{clade
 |1 = [[Biarmosuchia]]
 |2 = {{clade
  |1 = [[Dinocephalia]]
  |2 = {{clade
   |1 = [[Anomodontia]]
   |2 = {{clade
    |1 = [[Gorgonopsia]]
    |2 = {{clade
     |1 = [[Therocephalia]]
     |2 = [[Cynodontia]]
     }}
    }}
   }}
  }}
 }}
}}

}}
Six major groups of therapsids are generally recognized: Biarmosuchia, Dinocephalia, Anomodontia, Gorgonopsia, Therocephalia and Cynodontia. A clade uniting therocephalians and cynodonts, called [[Eutheriodontia]], is well supported, but relationships among the other four clades are controversial.<ref name=AngielczykKammerer2018/> The most widely accepted hypothesis of therapsid relationships, the Hopson and Barghausen paradigm, was first proposed in 1986. Under this hypothesis, biarmosuchians are the earliest-diverging major therapsid group, with the other five groups forming the Eutherapsida, and within Eutherapsida, gorgonopsians are the sister taxon of eutheriodonts, together forming the [[Theriodontia]]. Hopson and Barghausen did not initially come to a conclusion about how dinocephalians, anomodonts and theriodonts were related to each other, but subsequent studies suggested that anomodonts and theriodonts should be classified together as the Neotherapsida. However, there remains debate over these relationships; in particular, some studies have suggested that anomodonts, not gorgonopsians, are the sister taxon of Eutheriodontia, other studies have found dinocephalians and anomodonts to form a clade, and both the phylogenetic position and monophyly of Biarmosuchia remain controversial.

In addition to the six major groups, there are several other lineages and species of uncertain classification. ''[[Raranimus]]'' from the early Middle Permian of China is likely to be the earliest-diverging known therapsid.<ref>{{Cite journal |last1=Duhamel |first1=A. |last2=Benoit |first2=J. |last3=Rubidge |first3=B. S. |last4=Liu |first4=J. |name-list-style=amp |date=August 2021 |title=A re-assessment of the oldest therapsid Raranimus confirms its status as a basal member of the clade and fills Olson's gap |url=https://link.springer.com/10.1007/s00114-021-01736-y |journal=The Science of Nature |language=en |volume=108 |issue=4 |pages=26 |bibcode=2021SciNa.108...26D |doi=10.1007/s00114-021-01736-y |issn=0028-1042 |pmid=34115204 |s2cid=235403632|url-access=subscription }}</ref> ''[[Tetraceratops]]'' from the Early Permian of the United States has been hypothesized to be an even earlier-diverging therapsid,<ref name="Laurin1996"/><ref name="Amson2011"/> but more recent study has suggested it is more likely to be a non-therapsid sphenacodontian.<ref name="Spindler2020"/>
{{Further|topic=the dubious genus of non-mammalian therapsid|Cynodraco}}

===Biarmosuchia===
{{Main|Biarmosuchia}}
[[Image:Biarmosuchus BW.jpg|thumb|200px|''[[Biarmosuchus]]'', a [[biarmosuchia]]n]]

Biarmosuchia is the most recently recognized therapsid clade, first recognized as a distinct lineage by Hopson and Barghausen in 1986 and formally named by Sigogneau-Russell in 1989. Most biarmosuchians were previously classified as gorgonopsians. Biarmosuchia includes the distinctive [[Burnetiamorpha]], but support for the monophyly of Biarmosuchia is relatively low. Many biarmosuchians are known for extensive cranial ornamentation.

===Dinocephalia===
{{Main|Dinocephalia}}
[[Image:Titanophoneus_3.jpg|right|thumb|200px|Two genera of [[dinocephalia]]ns : ''[[Titanophoneus]]'' (an [[anteosaur]]) devouring a ''[[Ulemosaurus]]'' (a [[tapinocephalia]]n)]]
Dinocephalia comprises two distinctive groups, the [[Anteosauria]] and [[Tapinocephalia]].

Historically, carnivorous dinocephalians, including both anteosaurs and titanosuchids, were called titanosuchians and classified as members of Theriodontia, while the herbivorous Tapinocephalidae were classified as members of Anomodontia.

===Anomodontia===
{{Main|Anomodontia}}
[[Image:Lystr georg1DB.jpg|right|thumb|''[[Lystrosaurus]]'', a [[dicynodont]] anomodont]]
Anomodontia includes the dicynodonts, a clade of tusked, beaked herbivores, and the most diverse and long-lived clade of non-cynodont therapsids. Other members of Anomodontia include ''[[Suminia]],'' which is thought to have been a climbing form.

===Gorgonopsia===
{{Main|Gorgonopsia}}
[[Image:Inostrancevia BW.jpg|right|thumb|200px|''[[Inostrancevia]]'', a [[gorgonopsia]]n]]

Gorgonopsia is an abundant but morphologically homogeneous group of [[saber-toothed predator]]s.

===Therocephalia===
{{Main|Therocephalia}}
[[Image:Moschorhinus_DB.jpg|right|thumb|200px|''[[Moschorhinus]]'', a [[therocephalia]]n]]
It has been suggested that Therocephalia might not be monophyletic, with some species more closely related to cynodonts than others.<ref name=Abdala2008/> However, most studies regard Therocephalia as monophyletic.

===Cynodontia===
{{Main|Cynodontia}}
[[Image:Trucidocynodon_riograndensis.jpg|right|thumb|200px|''[[Trucidocynodon]]'', a non-[[mammal]]ian [[cynodont]]]]
Cynodonts are the most diverse and longest-lived of the therapsid groups, as Cynodontia includes mammals. Cynodonts are the only major therapsid clade to lack a Middle Permian fossil record, with the earliest-known cynodont being ''[[Charassognathus]]'' from the [[Wuchiapingian]] age of the Late Permian. Non-mammalian cynodonts include both carnivorous and herbivorous forms.

==See also==
* [[Evolution of mammals]]
* [[Timeline of the evolutionary history of life]]
* [[Vertebrate paleontology]]

==Notes==
{{Notelist}}

==References==
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==Further reading==
* Benton, M. J. (2004). ''Vertebrate Palaeontology'', 3rd ed., Blackwell Science.
* Carroll, R. L. (1988). ''Vertebrate Paleontology & Evolution''. W. H. Freeman & Company, New York.
* Kemp, T. S. (2005). ''The origin and evolution of mammals''. [[Oxford University Press]].
* Romer, A. S. (1966). ''Vertebrate Paleontology''. University of Chicago Press, 1933; 3rd ed.
* Bennett, A. F., & Ruben, J. A. (1986). "[https://compphys.bio.uci.edu/bennett/pubs/74.pdf The metabolic and thermoregulatory status of therapsids] {{Webarchive|url=https://web.archive.org/web/20230501055416/https://compphys.bio.uci.edu/bennett/pubs/74.pdf |date=1 May 2023 }}." In ''The ecology and biology of mammal-like reptiles''. Smithsonian Institution Press, Washington, DC, 207-218.
* {{cite book|url=https://doi.org/10.1007/978-94-007-6841-3 |doi=10.1007/978-94-007-6841-3 |title=Early Evolutionary History of the Synapsida |series=Vertebrate Paleobiology and Paleoanthropology |date=2014 |bibcode=2014eehs.book.....K |isbn=978-94-007-6840-6 |last1=Kammerer |first1=Christian F. |last2=Angielczyk |first2=Kenneth D. |last3=Fröbisch |first3=Jörg }}
* Ross, R.P., Ross, C.A. (2023). ''Permian Period, geochronology''. Encyclopedia Britannica. <nowiki>https://www.britannica.com/science/Permian-Period</nowiki>
* Padian, Kevin (2013-09). "A Review of "Forerunners of Mammals: Radiation, Histology, Biology"". ''Journal of Vertebrate Paleontology''. '''33''' (5): 1250–1251.

==External links==
{{Wikispecies|Therapsida}}
* "[http://tolweb.org/tree?group=Therapsida Therapsida: Mammals and extinct relatives]" ''Tree of Life''
* "[https://web.archive.org/web/20060617022445/http://www.palaeos.com/Vertebrates/Units/400Therapsida/400.000.html Therapsida: overview]" ''Palaeos''

{{Synapsida}}
{{Authority control}}
{{Taxonbar|from=Q322241}}

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[[Category:Therapsida| ]]
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[[Category:Cisuralian first appearances]]
[[Category:Extant Permian first appearances]]
[[Category:Taxa named by Robert Broom]]