Metatheria

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Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives.

Metatheria
Lycopsis longirostris.JPG
Lycopsis longirostris, an extinct sparassodont, a relative of the marsupials
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Clade: Metatheria
Huxley, 1880
Subgroups

There are three extant subclasses of mammals, one being metatherians:

  1. monotremes: egg laying mammals like the platypus and the echidna,
  2. metatheria: marsupials, which includes three American orders (Didelphimorphia, Paucituberculata and Microbiotheria) and four Australasian orders (Notoryctemorphia, Dasyuromorphia, Peramelemorphia and Diprotodontia),[4] and the
  3. eutherians: placental mammals, consisting of four superorders divided into 21 orders.[5]

Metatherians belong to a subgroup of the northern tribosphenic mammal clade or Boreosphenida. They differ from all other mammals in certain morphologies like their dental formula, which includes about five upper and four lower incisors, a canine, three premolars, and four molars.[6] Other characters include skeletal and anterior dentition, such as wrist and ankle apomorphies; all metatherians share derived pedal characters and calcaneal features. The earliest known members of the group are from the latter half of the Early Cretaceous in North America. Remains of metatherians have been found on all continents.

ClassificationEdit

Below is a metatherian cladogram from Wilson et al. (2016):[7]

Metatheria

Holoclemensia

Deltatheroida
Pappotheriidae

Pappotherium

Deltatheridiidae

Sulestes

Oklatheridium

Tsagandelta

Lotheridium

Deltatheroides

Deltatheridium

Nanocuris

Atokatheridium

Marsupialiformes

Gurlin Tsav skull

Borhyaenidae

Mayulestes

Jaskhadelphys

Andinodelphys

Pucadelphys

Asiatherium

Iugomortiferum

Kokopellia

Aenigmadelphys

Anchistodelphys

Glasbiidae

Glasbius

Pediomyidae

Pediomys

Stagodontidae

Pariadens

Eodelphis

Didelphodon

Turgidodon

Alphadon

Alphadontidae

Albertatherium

Marsupialia

Below is a listing of metatherians that do not fall readily into well-defined groups.

Basal Metatheria

Ameridelphia incertae sedis:

Marsupialia incertae sedis:

Evolutionary historyEdit

The relationships between the three extant divisions of mammals (monotremes, marsupials, and placental mammals) was long a matter of debate among taxonomists.[8] Most morphological evidence comparing traits, such as the number and arrangement of teeth and the structure of the reproductive and waste elimination systems, favors a closer evolutionary relationship between marsupials and placental mammals than either has with the monotremes, as does most genetic and molecular evidence.[9]

Fossil metatherians are distinguished from eutherians by the form of their teeth: metatherians possess four pairs of molar teeth in each jaw, whereas eutherian mammals (including true placentals) never have more than three pairs.[10] Using this criterion, the earliest known metatherian was formerly considered to be Sinodelphys szalayi, which lived in China around 125 million years ago (mya).[11] This makes it a contemporary to some early eutherian species that have been found in the same area.[12] However, Bi et al. (2018) reinterpreted Sinodelphys as an early member of Eutheria. The oldest uncontested metatherians are now 110 million year old fossils from western North America.[3] Metatherians were widespread in Asia and North America during the Late Cretaceous, including both Deltatheroida and Marsupaliformes. Metatherians underwent a severe decline during the K-Pg extinction event, more severe than that suffered by contemporary eutherians and multituberculates, and were slower to recover diversity.[13]

Morphological and species diversity of metatherians in Laurasia remained low in comparison to eutherians throughout the Cenozoic.[14] The two major groups of Cenozoic Laurasian metatherians, the herpetotheriids and peradectids persisted into the Miocene before becoming extinct, with the North American herpetotheriid Herpetotherium, the European herpetotheriid Amphiperatherium and the peradectids Siamoperadectes and Sinoperadectes from Asia being the youngest Laurasian metatherians.[15][13] Metatherians first arrived in Afro-Arabia during the Paleogene, probably from Europe, including the possible peradectoid Kasserinotherium from the Early Eocene of Tunisia and the herpetotheriid Peratherium africanum from the Early Oligocene of Egypt and Oman. The youngest African metatherian is the possible herpetotheriid Morotodon from the late Early Miocene of Uganda.[16][17]

Metatherians arrived in South America from North America during the Paleocene and underwent a major diversificiation, with South American metatherians including both the ancestors of extant marsupials as well as the extinct Sparassodonta, which were major predators in South American ecosystems during most of the Cenozoic, up until their extinction in the Pliocene, as well as the Polydolopimorphia, which likely had a wide range of diets.[14] The oldest known Australian marsupials are known from the early Eocene, and are thought to have arrived in the region after having dispersed from Antarctica. The only known Antarctic metatherians are from the Early Eocene La Meseta Formation of the Antarctic Peninsula, where they are the most diverse group of mammals, and include marsupials as well as polydolopimorphians.[14]

ReferencesEdit

  1. ^ O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Michael J.; Novacek, Fernando A.; Perini, Zachary S.; Randall, Guillermo; Rougier, Eric J.; Sargis, Mary T.; Silcox, Nancy b.; Simmons, Micelle; Spaulding, Paul M.; Velazco, Marcelo; Weksler, John R.; Wible, Andrea L.; Cirranello, A. L. (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. Bibcode:2013Sci...339..662O. doi:10.1126/science.1229237. hdl:11336/7302. PMID 23393258. S2CID 206544776.
  2. ^ C.V. Bennett, P. Francisco, F. J. Goin, A. Goswami (2018). "Deep time diversity of metatherian mammals: implications for evolutionary history and fossil-record quality". Paleobiology. 44 (2): 171–198. doi:10.1017/pab.2017.34.{{cite journal}}: CS1 maint: uses authors parameter (link)
  3. ^ a b S. Bi, X. Zheng, X. Wang, N.E. Cignetti, S. Yang, J.R. Wible (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. PMID 29899454. S2CID 49183466.{{cite journal}}: CS1 maint: uses authors parameter (link)
  4. ^ Nilsson, Maria A. (2010). "Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions". PLOS Biology. 8 (7): e1000436. doi:10.1371/journal.pbio.1000436. PMC 2910653. PMID 20668664.
  5. ^ Wilson, Don E.; Reeder, DeeAnn M. (editors) (2005). Microtus (Mynomes) townsendii. Wilson and Reeder’s Mammal Species of the World – A Taxonomic and Geographic Reference (Print) (Third ed.). Baltimore, Maryland: Johns Hopkins University Press/Bucknell University. pp. 2, 142. ISBN 978-0-8018-8221-0. Retrieved 21 October 2014. {{cite book}}: |first2= has generic name (help)
  6. ^ Szalay, Frederick S. (11 May 2006). Evolutionary History of the Marsupials and an Analysis of Osteological ... ISBN 9780521025928.
  7. ^ Wilson, G.P.; Ekdale, E.G.; Hoganson, J.W.; Calede, J.J.; Linden, A.V. (2016). "A large carnivorous mammal from the Late Cretaceous and the North American origin of marsupials". Nature Communications. 7: 13734. Bibcode:2016NatCo...713734W. doi:10.1038/ncomms13734. PMC 5155139. PMID 27929063.
  8. ^ Moyal, Ann Mozley (2004). Platypus: The Extraordinary Story of How a Curious Creature Baffled the World. Baltimore: The Johns Hopkins University Press. ISBN 978-0-8018-8052-0.
  9. ^ van Rheede, T.; Bastiaans, T.; Boone, D.; Hedges, S.; De Jong, W.; Madsen, O. (2006). "The platypus is in its place: nuclear genes and indels confirm the sister group relation of monotremes and therians". Molecular Biology and Evolution. 23 (3): 587–597. doi:10.1093/molbev/msj064. PMID 16291999.
  10. ^ Benton, Michael J. (1997). Vertebrate Palaeontology. London: Chapman & Hall. p. 306. ISBN 978-0-412-73810-4.
  11. ^ Rincon, Paul (12 December 2003). "Oldest Marsupial Ancestor Found, BBC, Dec 2003". BBC News. Retrieved 16 March 2010.
  12. ^ Hu, Yaoming; Meng, Jin; Li, Chuankui; Wang, Yuanqing (2010). "New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China". Proceedings of the Royal Society B. 277 (1679): 229–236. doi:10.1098/rspb.2009.0203. PMC 2842663. PMID 19419990.
  13. ^ a b Bennett, C. Verity; Upchurch, Paul; Goin, Francisco J.; Goswami, Anjali (6 February 2018). "Deep time diversity of metatherian mammals: implications for evolutionary history and fossil-record quality". Paleobiology. 44 (2): 171–198. doi:10.1017/pab.2017.34. ISSN 0094-8373.
  14. ^ a b c Eldridge, Mark D B; Beck, Robin M D; Croft, Darin A; Travouillon, Kenny J; Fox, Barry J (23 May 2019). "An emerging consensus in the evolution, phylogeny, and systematics of marsupials and their fossil relatives (Metatheria)". Journal of Mammalogy. 100 (3): 802–837. doi:10.1093/jmammal/gyz018. ISSN 0022-2372.
  15. ^ Furió, Marc; Ruiz-Sánchez, Francisco J.; Crespo, Vicente D.; Freudenthal, Matthijs; Montoya, Plinio (July 2012). "The southernmost Miocene occurrence of the last European herpetotheriid Amphiperatherium frequens (Metatheria, Mammalia)". Comptes Rendus Palevol. 11 (5): 371–377. doi:10.1016/j.crpv.2012.01.004.
  16. ^ Crespo, Vicente D.; Goin, Francisco J. (21 June 2021). "TAXONOMY AND AFFINITIES OF AFRICAN CENOZOIC METATHERIANS". Spanish Journal of Palaeontology. 36 (2). doi:10.7203/sjp.36.2.20974. ISSN 2255-0550.
  17. ^ Crespo, Vicente D.; Goin, Francisco J.; Pickford, Martin (3 June 2022). "The last African metatherian". Fossil Record. 25 (1): 173–186. doi:10.3897/fr.25.80706. ISSN 2193-0074.