Theria
Theria | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Clade: | Tribosphenida |
Subclass: | Theria Haswell, 1897[1]
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Subgroups | |
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Theria (
Characteristics
Therian mammals give birth (see
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.
The flexible nose in therian mammals is not found in any other vertebrates, and is the product of modified cells involved in the development of the upper jaw in other tetrapods.[6]
Evolution
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.[7][8] Further, King and Beck in 2020 argue for an Early Cretaceous age for Juramaia sinensis, in line with similar early mammaliaformes.[9]
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.[10]
Molecular data suggests that therians may have originated even earlier, during the Early Jurassic.[11] Therian mammals began to diversify 10-20 million years before the dinosaur extinction.[12]
Taxonomy
The rank of "Theria" may vary depending on the classification system used. The textbook classification system by Vaughan et al. (2000)[13] gives the following:
Class Mammalia
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In the above system Theria is a subclass. Alternatively, in the system proposed by McKenna and Bell (1997)[14] it is ranked as a supercohort under the subclass Theriiformes:
Class Mammalia
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Another classification proposed by Luo et al. (2002)[15] does not assign any rank to the taxonomic levels, but uses a purely cladistic system instead.
See also
- Marsupials
- Marsupionta
- Monotremes
- Placental mammals
- Patagomaia chainko
References
- ^ ITIS Standard Report Page: Theria
- ^ Myers, P.; R. Espinosa; C. S. Parr; T. Jones; G. S. Hammond & T. A. Dewey. "Subclass Theria". Animal Diversity Web.
- PMID 25605903.
- ^ "Ancient "genomic parasites" spurred evolution of pregnancy in mammals". UChicago Medicine. January 29, 2015. Archived from the original on Jan 14, 2024.
- PMID 22951979.
- ^ Mammalian face as an evolutionary novelty - PMC
- S2CID 49183466.
- .
- PMID 32517606.
- 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.
- ISBN 0-03-025034-X
- 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.