Metatheria

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 slightly more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives.

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 twenty-one orders, divided into four superorders.[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 morphologies include skeletal and anterior dentition, such as wrist and ankle apomorphies; all metatherians share derived pedal characters and calcaneal features.

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

Classification

Below is a metatherian cladogram from Wilson et al. (2016):,[7] with addition of Sinodelphys from Luo et al. (2003/11):[8]

Metatheria

Sinodelphys

Holoclemensia

Pappotherium

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

Alphadontidae

Turgidodon

Alphadon

Albertatherium

Marsupialia

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

Basal Metatheria

  • Archaeonothos henkgodthelpi Beck 2015
  • Esteslestes ensis Novacek et al. 1991
  • Ghamidtherium dimaiensis Sánches-Villagra et al. 2007
  • Kasserinotherium tunisiense Crochet 1989
  • Palangania brandmayri Goin et al. 1998
  • Perrodelphys coquinense Goin et al. 1999

Ameridelphia incertae sedis:

  • Apistodon exiguus (Fox 1971) Davis 2007
  • Cocatherium lefipanum Goin et al. 2006
  • Dakotadens morrowi Eaton 1993
  • Iugomortiferum thoringtoni Cifelli 1990b
  • Marambiotherium glacialis Goin et al. 1999
  • Marmosopsis juradoi Paula Couto 1962 [Marmosopsini Kirsch & Palma 1995]
  • Pascualdelphys fierroensis
  • Progarzonia notostylopense Ameghino 1904
  • Protalphadon Cifelli 1990

Marsupialia incertae sedis:

  • Itaboraidelphys camposi Marshall & de Muizon 1984
  • Mizquedelphys pilpinensis Marshall & de Muizon 1988
  • Numbigilga ernielundeliusi Beck et al. 2008 {Numbigilgidae Beck et al. 2008}

Evolutionary history

The relationships between the three extant divisions of mammals (monotremes, marsupials, and placental mammals) was long a matter of debate among taxonomists.[9] 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.[10]

Around the end of the Triassic period, a Therapsid developed traits or characteristics that are diagnostic of the class Mammalia. This class gave rise to Multituberculata (herbivorous mammals), Triconodonta and Symmetrodonta (carnivorous and insectivorous mammals). However, these are not seen after the end of the Early Cretaceous and by the Late Cretaceous marsupials and placentals had evolved from a common eupantotherian ancestor.[6] The Mammalia class probably saw its first eutherian in the early Cretaceous Jehol biota in China called Acristatherium yanesis. This eutherian was determined to be the most basal based on a phylogenetic analysis that used a data matrix of many other species.[11] Metatherians probably evolved to take advantage of open arboreal niches. Adaptive radiation of marsupials excluded competition with their terrestrial placental counterparts.

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.[12] Using this criterion, the earliest known metatherian is Sinodelphys szalayi, which lived in China around 125 million years ago (mya). This 2003 study presents a new fossil from the early Cretaceous Yixian formation in China called Sinodelphys szalayi that gives enough morphological data to possibly be a basal metatherian in its didelphid-like morphology; it shares derived traits, such as dental formation and wrist and ankle structures. The fossil is about 125 million years old, making it one of the oldest metatherian fossils found and gives support to the claim that Asia was probably the center for diversification during the early Cretaceous. The researchers hypothesize that the divergence of Metatheria from Eutheria occurred in Asia no later than 125 million years ago, followed by the evolution of deltatheroidian-like taxa in Asia and North America about 120-100 million years ago and then the Paleocene diversification of relatives to the crown marsupials in South America.[13] This makes it a contemporary to some early eutherian species that have been found in the same area.[11]

The oldest metatherian fossils are found in present-day China.[14] About 100 mya, the supercontinent Pangaea was in the process of splitting into the northern continent Laurasia and the southern continent Gondwana, with what would become China and Australia already separated by the Tethys Ocean. From there, metatherians spread westward into modern North America (still attached to Eurasia), where the earliest true marsupials are found. It is difficult to identify which fossils are marsupials, as they are characterized by aspects of the reproductive system that do not normally fossilize (such as pouches) and by subtle changes in the bone and tooth structure that show a metatherian is part of the marsupial crown group (the most exclusive group that contains all living marsupials). The earliest definite marsupial fossil belongs to the species Peradectes minor, from the Paleocene of Montana, dated to about 65 million years ago.[1] From this point of origin in Laurasia, marsupials spread to South America, which was connected to North America until around 65 mya. Laurasian marsupials eventually died off; traditionally this has been assumed to be due to competition with placental mammals, but generally this is no longer considered to be the case, as metatherian diversity doesn't seem to be correlated to placental diversity.[15][16] Indeed, it appears metatherians suffered the heaviest mammalian casualties in the KT event, taking longer to recover than other groups.[17] In Laurasian landmasses, herpetotheriids and peradectids remained alive until the mid to late Miocene, with the peradectids Siamoperadectes and Sinoperadectes being the youngest Laurasian metatherians.

See also

References

  1. ^ a b 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. doi:10.1126/science.1229237. PMID 23393258.
  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.CS1 maint: uses authors parameter (link)
  3. ^ S. Bi, X. Zheng, X. Wang, N.E. Cignetti, S. Yang, J.S. Wible (2018). "An Early Cretaceous eutherian and the placental–marsupial dichotomy". Nature. 558 (7710): 390–395. doi:10.1038/s41586-018-0210-3. PMID 29899454.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.CS1 maint: extra text: authors list (link)
  6. ^ a b 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. doi:10.1038/ncomms13734. PMC 5155139. PMID 27929063.
  8. ^ https://www.researchgate.net/publication/8963678_An_Early_Cretaceous_Tribosphenic_Mammal_and_Metatherian_Evolution
  9. ^ 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.
  10. ^ 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.
  11. ^ a b 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.
  12. ^ Benton, Michael J. (1997). Vertebrate Palaeontology. London: Chapman & Hall. p. 306. ISBN 978-0-412-73810-4.
  13. ^ Rincon, Paul (12 December 2003). "Oldest Marsupial Ancestor Found, BBC, Dec 2003". BBC News. Retrieved 16 March 2010.
  14. ^ Luo, Zhe-Xi; Ji, Qiang; Wible, John R.; Yuan, Chong-Xi (12 December 2003). "An early Cretaceous tribosphenic mammal and metatherian evolution". Science. 302 (5652): 1934–1940. doi:10.1126/science.1090718. PMID 14671295.
  15. ^ Sánchez-Villagra, Marcelo, Why are There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity, December 2013, Volume 20, Issue 4, pp 279-290
  16. ^ Carter, AM; Mess, AM (2013). "Conservation of placentation during the tertiary radiation of mammals in South America". J Morphol. 274 (5): 557–69. doi:10.1002/jmor.20120. PMID 23355381.
  17. ^ Mathias M. Pires; Brian D. Rankin; Daniele Silvestro; Tiago B. Quental (2018). "Diversification dynamics of mammalian clades during the K–Pg mass extinction". Biology Letters. 14 (9): 20180458. doi:10.1098/rsbl.2018.0458. PMC 6170748. PMID 30258031.
Ameridelphia

Ameridelphia is traditionally a superorder that includes all marsupials living in the Americas except for the Monito del monte (Dromiciops). It is now regarded as a paraphyletic group.

Anatoliadelphys

Anatoliadelphys maasae is an extinct genus of predatory metatherian mammal from the Eocene of Europe. It was an arboreal, cat-sized animal, with powerful crushing jaws similar to those of the modern Tasmanian devil. Although most mammalian predators of the northern hemisphere in this time period were placentals, Europe was an archipelago, and the island landmass now forming Turkey might have been devoid of competing mammalian predators, though this may not matter since other carnivorous metatherians are also known from the Cenozoic in the Northern Hemisphere. Nonetheless, it stands as a reminder that mammalian faunas in the Paleogene of the Northern Hemisphere were more complex than previously thought, and metatherians did not lose their hold as major predators after their success in the Cretaceous.

Arcantiodelphys

Arcantiodelphys is an extinct genus of basal Metatheria which existed in France during the Cenomanian age. It was first named by Romain Vullo, Emmanuel Gheerbrant, Christian de Muizon and Didier Néraudeau in 2009 and the type species is Arcantiodelphys marchandi.

Australidelphia

Australidelphia is the superorder that contains roughly three-quarters of all marsupials, including all those native to Australasia and a single species from South America (all other American marsupials are members of the Ameridelphia). Analysis of retrotransposon insertion sites in the nuclear DNA of a variety of marsupials has shown that the South American monito del monte's lineage is the most basal of the superorder.The Australian australidelphians form a clade, for which the name Euaustralidelphia ("true Australidelphia") has been proposed (the branching order within this group is yet to be determined). The study also showed that the most basal of all marsupial orders are the other two South American groups (Didelphimorphia and Paucituberculata, with the former probably branching first). This indicates that Australidelphia arose in South America along with the other major divisions of extant marsupials, and likely reached Australia via Antarctica in a single dispersal event after Microbiotheria split off.

Borhyaena

Borhyaena is an extinct genus of South American metatherian, living between 17.5 and 15.5 million years ago in Patagonia, Argentina (Santa Cruz and Sarmiento Formations) and Chile (Río Frias Formation).

Cladotheria

Cladotheria is a group (legion) of mammals that includes the ancestor of Dryolestoidea, Peramuridae and Zatheria (living therians plus all of its ancestors).

Eutheria

Eutheria (; from Greek εὐ-, eu- "good" or "right" and θηρίον, thēríon "beast" hence "true beasts") is one of two mammalian clades with extant members that diverged in the Early Cretaceous or perhaps the Late Jurassic. Except for the North American Virginia opossum, which is a metatherian, all post-Miocene mammals indigenous to Europe, Africa, Asia, and North America north of Mexico are eutherians. Extant eutherians, their last common ancestor, and all extinct descendants of that ancestor are members of Placentalia.

Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy.The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the Jurassic in China.Eutheria was named in 1872 by Theodore Gill; in 1880 Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia.

Gurlin Tsav skull

The "Gurlin Tsav" skull is a currently unnamed carnivorous metatherian fossil from the Nemegt Formation of Mongolia. Composed of a single semi-complete skull, this specimen is notable in regards to the evolution and systematics of Metatheria as a whole, and thus nigh-omnipresent in phylogenetic analyses of this group.

Oklatheridium

Oklatheridium is an extinct genus of deltatheroidan.

Pharsophorus

Pharsophorus is an extinct genus of borhyaenoid sparassodont that inhabited South America during the Middle to Late Oligocene epoch.

Polydolopimorphia

Polydolopimorphia is an extinct order of Metatherians, more closely related to extant Marsupials than other extinct mammals. Known from the Paleocene-Pliocene of South America and the Eocene of Antarctica, they were a diverse group during the Paleogene, filling many niches, before declining and becoming extinct at the end of the Neogene. It is divided into two suborders, Bonapartheriiformes, and Polydolopiformes

Proborhyaenidae

Proborhyaenidae is an extinct family of metatherian mammals of the order Sparassodonta, which lived in South America from the Eocene (Mustersan) until the Oligocene (Deseadan). Sometimes it has been included as a subfamily of their relatives, the borhyaenids (as Proborhyaeninae). Body mass estimates suggest that proborhyaenids could weigh up to 150 kilograms (330 lb), making them some of the largest known metatherians. Proborhyaenid remains have been found in western Bolivia, Uruguay, southern Brazil, and the provinces of Mendoza, Salta, and Chubut, in Argentina.Most proborhyaenids had a robust, hyena-like skull, although one species, Callistoe vincei, had an elongate, narrow skull more reminiscent of a thylacine. The teeth were strongly specialized as carnassials for eating meat, and in Arminiheringia rotated throughout the animal's life to maintain a continuous shearing blade on the tooth. Preserved specimens of their canines lack enamel; in life, the enamel may have been very thin or restricted to the tooth tips. In the genus Arminiheringia the lower canines are protruding. Proborhyaenids can be distinguished from other sparassodonts by their grooved upper and lower canines, which grew continuously throughout the animals' lives like rodent incisors. Bond and Pascual (1983) argued that proborhyaenid canines stopped growing in late adulthood based on a specimen from Mendoza Province, Argentina, but the proborhyaenid identity of this specimen is disputed. The presence of open-rooted upper canines in thylacosmilids has led to the suggestion that proborhyaenids are closely related to, or even ancestral to, this group, but this is still controversial.

Prothylacinus

Prothylacinus is an extinct genus of South American metatherian, that lived during the Early Miocene.

Siamoperadectes

Siamoperadectes is a genus of non-marsupial metatherian from the Miocene of Thailand. A member of Peradectidae, it is the first member of its clade known from South Asia, and among the last non-marsupial metatherians.

Sparassodonta

Sparassodonta (from Greek σπαράσσειν [sparassein], to tear, rend; and ὀδούς, gen. ὀδόντος [odous, odontos], tooth) is an extinct order of carnivorous metatherian mammals native to South America. They were once considered to be true marsupials, but are now thought to be either a sister taxon to them, or considerably distantly related, part of a separate clade of Gondwanan metatherians. A number of these mammalian predators closely resemble placental predators that evolved separately on other continents, and are cited frequently as examples of convergent evolution. They were first described by Florentino Ameghino, from fossils found in the Santa Cruz beds of Patagonia. Sparassodonts were present throughout South America's long period of "splendid isolation" during the Cenozoic; during this time, they shared the niches for large warm-blooded predators with the flightless terror birds. Previously, it was thought that these mammals died out in the face of competition from "more competitive" placental carnivorans during the Pliocene Great American Interchange, but more recent research has showed that sparassodonts died out long before eutherian carnivores arrived in South America (aside from procyonids).

Stagodontidae

Stagodontidae is an extinct family of carnivorous metatherian mammals that inhabited North America during the late Cretaceous, and possibly to the Eocene in South America.

Theriiformes

Theriiformes is a subclass of mammals. The term was coined in 1997 by McKenna & Bell in their classification of mammals. In the strict sense, it is defined as all mammals more closely related to therians than to monotremes.

Thylacosmilidae

Thylacosmilidae is an extinct family of metatherian predators, related to the modern marsupials, which lived in South America between the Miocene and Pliocene epochs. Like other South American mammalian predators that lived prior to the Great American Biotic Interchange, these animals belonged to the order Sparassodonta, which occupied the ecological niche of many eutherian mammals of the order Carnivora from other continents. The family's most notable feature are the elongated, laterally flattened fangs, which is a remarkable evolutionary convergence with other saber-toothed mammals like Barbourofelis and Smilodon.

Zatheria

Zatheria is a group (sublegion) of mammals that includes the common ancestor of Arguimuridae, Vincelestidae, Peramuridae and Tribosphenida (living therians plus all of its ancestors).

Extant mammal orders
Yinotheria
Theria

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