Therian mammals give birth (see viviparity) to live young without a shelled egg. This is possible thanks to key proteins called syncytins which allow exchanges between the mother and its offspring through a placenta, even rudimental ones such as in marsupials. Genetic studies have suggested a viral origin of syncytins through the endogenization process.[3]
The marsupials and the placental mammals evolved from a common therian ancestor that gave live birth by suppressing the mother's immune system. While the marsupials continued to give birth to an underdeveloped fetus after a short pregnancy, the ancestors of placental mammals gradually evolved a prolonged pregnancy.[4]
Therian mammals no longer have the coracoid bone, unlike their cousins, monotremes.
Pinnae (external ears) are also a distinctive trait that is a therian exclusivity, though some therians, such as the earless seals, have lost them secondarily.[5]
Evolutionedit
The earliest known therian mammal fossil is Juramaia, from China's Late Jurassic (Oxfordian stage). However, the age estimates of the site are disputed based on the geological complexity and the geographically widespread nature of the Tiaojishan Formations.[6][7] Further, King and Beck in 2020 argue for an Early Cretaceous age for Juramaia sinensis, in line with similar early mammaliaformes.[8]
A recent review of the Southern Hemisphere Mesozoic mammal fossil record has argued that triosphenic mammals arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade's earliest undisputed appearance in the Northern Hemisphere.[9]
Molecular data suggests that therians may have originated even earlier, during the Early Jurassic.[10] Therian mammals began to diversify 10-20 million years before the dinosaur extinction.[11]
The rank of "Theria" may vary depending on the classification system used. The textbook classification system by Vaughan et al. (2000)[12] gives the following:
In the above system Theria is a subclass. Alternatively, in the system proposed by McKenna and Bell (1997)[13] it is ranked as a supercohort under the subclass Theriiformes:
^Myers, P.; R. Espinosa; C. S. Parr; T. Jones; G. S. Hammond & T. A. Dewey. "Subclass Theria". Animal Diversity Web.
^Cornelis, G.; Vernochet, C.; Carradec, Q.; Souquere, S.; Mulot, B.; Catzeflis, F.; Nilsson, M. A.; Menzies, B. R.; Renfree, M. B.; Pierron, G.; Zeller, U.; Heidmann, O.; Dupressoir, A.; Heidmann, T. (2015). "Retroviral envelope gene captures and syncytin exaptation for placentation in marsupials". Proceedings of the National Academy of Sciences of the United States of America. 112 (5): E487–E496. Bibcode:2015PNAS..112E.487C. doi:10.1073/pnas.1417000112. PMC4321253. PMID 25605903.
^"Ancient "genomic parasites" spurred evolution of pregnancy in mammals". UChicago Medicine. January 29, 2015. from the original on Jan 14, 2024.
^SUMIYAMA K; MIYAKE T; GRIMWOOD J; STUART A; DICKSON M; SCHMUTZ J; RUDDLE FH; MYERS RM; AMEMIYA CT (2012). "Theria-Specific Homeodomain and cis-Regulatory Element Evolution of the Dlx3–4 Bigene Cluster in 12 Different Mammalian Species". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 318 (8): 639–650. doi:10.1002/jez.b.22469. PMC3651898. PMID 22951979.
^Bi, Shundong; Zheng, Xiaoting; Wang, Xiaoli; Cignetti, Natalie E.; Yang, Shiling; Wible, John R. (June 2018). "An Early Cretaceous eutherian and the placental-marsupial dichotomy". Nature. 558 (7710): 390–395. Bibcode:2018Natur.558..390B. doi:10.1038/s41586-018-0210-3. ISSN 1476-4687. PMID 29899454. S2CID 49183466.
^Meng, Jin (2014). "Mesozoic mammals of China: implications for phylogeny and early evolution of mammals". National Science Review. 1 (4): 521–542. doi:10.1093/nsr/nwu070.
^King, Benedict; Beck, Robin M. D. (2020-06-10). "Tip dating supports novel resolutions of controversial relationships among early mammals". Proceedings of the Royal Society B: Biological Sciences. 287 (1928): 20200943. doi:10.1098/rspb.2020.0943. ISSN 0962-8452. PMC7341916. PMID 32517606.
^Flannery, Timothy F.; Rich, Thomas H.; Vickers-Rich, Patricia; Veatch, E. Grace; Helgen, Kristofer M. (2022-10-02). "The Gondwanan Origin of Tribosphenida (Mammalia)". Alcheringa: An Australasian Journal of Palaeontology. 46 (3–4): 277–290. Bibcode:2022Alch...46..277F. doi:10.1080/03115518.2022.2132288. ISSN 0311-5518.
^ Hugall, A.F. et al. (2007) Calibration choice, rate smoothing, and the pattern of tetrapod diversification according to the long nuclear gene RAG-1. Syst Biol. 56(4):543-63.
^Golembiewski, Kate (2 June 2016). "Mammals began their takeover long before the death of the dinosaurs". Field Museum of Natural History. from the original on 8 January 2022. Retrieved 8 January 2022.
^Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. 2000. Mammalogy: Fourth Edition. Saunders College Publishing, 565 pp. ISBN0-03-025034-X
^McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN0-231-11013-8
^Luo, Z.-X., Z. Kielan-Jaworowska, and R. L. Cifelli. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica, 47:1-78.
theria, redirects, here, contemporary, subculture, nthropy, modern, therianthropy, moth, genus, moth, ɪər, from, ancient, greek, θηρίον, thēríon, wild, beast, subclass, mammals, amongst, theriiformes, includes, eutherians, including, placental, mammals, metath. Therians redirects here For the contemporary subculture see Therianthropy Modern therianthropy For the moth genus see Theria moth Theria ˈ 8 ɪer i e or ˈ 8 ɛr i e from Ancient Greek 8hrion therion wild beast is a subclass of mammals 2 amongst the Theriiformes Theria includes the eutherians including the placental mammals and the metatherians including the marsupials but excludes the egg laying monotremes and various extinct mammals evolving prior to the common ancestor of placentals and marsupials TheriaTemporal range Late Jurassic recent 161 0 Ma PreꞒ Ꞓ O S D C P T J K Pg NScientific classificationDomain EukaryotaKingdom AnimaliaPhylum ChordataClass MammaliaClade TribosphenidaSubclass TheriaParker amp Haswell 1897 1 SubgroupsClade Eutheria Clade Metatheria Genus Patagomaia Genus Spelaeomolitor Incertae sedis Genus Tingamarra Contents 1 Characteristics 2 Evolution 3 Taxonomy 4 See also 5 References 6 External linksCharacteristics editTherian mammals give birth see viviparity to live young without a shelled egg This is possible thanks to key proteins called syncytins which allow exchanges between the mother and its offspring through a placenta even rudimental ones such as in marsupials Genetic studies have suggested a viral origin of syncytins through the endogenization process 3 The marsupials and the placental mammals evolved from a common therian ancestor that gave live birth by suppressing the mother s immune system While the marsupials continued to give birth to an underdeveloped fetus after a short pregnancy the ancestors of placental mammals gradually evolved a prolonged pregnancy 4 Therian mammals no longer have the coracoid bone unlike their cousins monotremes Pinnae external ears are also a distinctive trait that is a therian exclusivity though some therians such as the earless seals have lost them secondarily 5 Evolution editThe earliest known therian mammal fossil is Juramaia from China s Late Jurassic Oxfordian stage However the age estimates of the site are disputed based on the geological complexity and the geographically widespread nature of the Tiaojishan Formations 6 7 Further King and Beck in 2020 argue for an Early Cretaceous age for Juramaia sinensis in line with similar early mammaliaformes 8 A recent review of the Southern Hemisphere Mesozoic mammal fossil record has argued that triosphenic mammals arose in the Southern Hemisphere during the Early Jurassic around 50 million years prior to the clade s earliest undisputed appearance in the Northern Hemisphere 9 Molecular data suggests that therians may have originated even earlier during the Early Jurassic 10 Therian mammals began to diversify 10 20 million years before the dinosaur extinction 11 Taxonomy editMain article Mammal classification The rank of Theria may vary depending on the classification system used The textbook classification system by Vaughan et al 2000 12 gives the following Class Mammalia Subclass Theria live bearing mammals Infraclass Metatheria marsupials Infraclass Eutheria placentalsIn the above system Theria is a subclass Alternatively in the system proposed by McKenna and Bell 1997 13 it is ranked as a supercohort under the subclass Theriiformes Class Mammalia Subclass Theriiformes live bearing mammals and their prehistoric relatives Infraclass Holotheria modern live bearing mammals and their prehistoric relatives Legion Cladotheria Sublegion Zatheria Infralegion Tribosphenida Supercohort Theria therian mammals Cohort Marsupialia marsupials Cohort Placentalia placentalsAnother classification proposed by Luo et al 2002 14 does not assign any rank to the taxonomic levels but uses a purely cladistic system instead See also editMarsupials Marsupionta Monotremes Placental mammalsReferences edit ITIS Standard Report Page Theria Myers P R Espinosa C S Parr T Jones G S Hammond amp T A Dewey Subclass Theria Animal Diversity Web Cornelis G Vernochet C Carradec Q Souquere S Mulot B Catzeflis F Nilsson M A Menzies B R Renfree M B Pierron G Zeller U Heidmann O Dupressoir A Heidmann T 2015 Retroviral envelope gene captures and syncytin exaptation for placentation in marsupials Proceedings of the National Academy of Sciences of the United States of America 112 5 E487 E496 Bibcode 2015PNAS 112E 487C doi 10 1073 pnas 1417000112 PMC 4321253 PMID 25605903 Ancient genomic parasites spurred evolution of pregnancy in mammals UChicago Medicine January 29 2015 Archived from the original on Jan 14 2024 SUMIYAMA K MIYAKE T GRIMWOOD J STUART A DICKSON M SCHMUTZ J RUDDLE FH MYERS RM AMEMIYA CT 2012 Theria Specific Homeodomain and cis Regulatory Element Evolution of the Dlx3 4 Bigene Cluster in 12 Different Mammalian Species Journal of Experimental Zoology Part B Molecular and Developmental Evolution 318 8 639 650 doi 10 1002 jez b 22469 PMC 3651898 PMID 22951979 Bi Shundong Zheng Xiaoting Wang Xiaoli Cignetti Natalie E Yang Shiling Wible John R June 2018 An Early Cretaceous eutherian and the placental marsupial dichotomy Nature 558 7710 390 395 Bibcode 2018Natur 558 390B doi 10 1038 s41586 018 0210 3 ISSN 1476 4687 PMID 29899454 S2CID 49183466 Meng Jin 2014 Mesozoic mammals of China implications for phylogeny and early evolution of mammals National Science Review 1 4 521 542 doi 10 1093 nsr nwu070 King Benedict Beck Robin M D 2020 06 10 Tip dating supports novel resolutions of controversial relationships among early mammals Proceedings of the Royal Society B Biological Sciences 287 1928 20200943 doi 10 1098 rspb 2020 0943 ISSN 0962 8452 PMC 7341916 PMID 32517606 Flannery Timothy F Rich Thomas H Vickers Rich Patricia Veatch E Grace Helgen Kristofer M 2022 10 02 The Gondwanan Origin of Tribosphenida Mammalia Alcheringa An Australasian Journal of Palaeontology 46 3 4 277 290 Bibcode 2022Alch 46 277F doi 10 1080 03115518 2022 2132288 ISSN 0311 5518 Hugall A F et al 2007 Calibration choice rate smoothing and the pattern of tetrapod diversification according to the long nuclear gene RAG 1 Syst Biol 56 4 543 63 Golembiewski Kate 2 June 2016 Mammals began their takeover long before the death of the dinosaurs Field Museum of Natural History Archived from the original on 8 January 2022 Retrieved 8 January 2022 Vaughan Terry A James M Ryan and Nicholas J Czaplewski 2000 Mammalogy Fourth Edition Saunders College Publishing 565 pp ISBN 0 03 025034 X McKenna Malcolm C and Bell Susan K 1997 Classification of Mammals Above the Species Level Columbia University Press New York 631 pp ISBN 0 231 11013 8 Luo Z X Z Kielan Jaworowska and R L Cifelli 2002 In quest for a phylogeny of Mesozoic mammals Acta Palaeontologica Polonica 47 1 78 External links edit nbsp Wikimedia Commons has media related to Theria Theria supercohort Tree of Life permanent dead link Retrieved from https en wikipedia org w index php title Theria amp oldid 1207001491, wikipedia, wiki, book, books, library,
