Theria

Theria (/ˈθɪəriə/; Greek: θηρίον theríon, wild beast) is a subclass of mammals[2] amongst the Theriiformes (the sister taxon to Yinotheria). Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials).

Therians
Temporal range: Late JurassicHolocene, 160–0 Ma
Cohunu koala, 2013(6)
A human (placental) holding two koalas, (marsupial), representing the two extant infraclasses of therian mammals.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Tribosphenida
Subclass: Theria
Parker & Haswell, 1897[1]
Infraclasses

Characteristics

Therian mammals give birth 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 the 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, contrary to 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

The earliest known therian mammal fossil is Juramaia, from the Late Jurassic (Oxfordian stage) of China. However, molecular data suggests that therians may have originated even earlier, during the Early Jurassic.[6]

Taxonomy

The rank of "Theria" may vary depending on the classification system used. The textbook classification system by Vaughan et al. (2000)[7] gives the following:

Class Mammalia

  • Subclass Theria: live-bearing mammals

In the above system Theria is a subclass. Alternatively, in the system proposed by McKenna and Bell (1997)[8] it is ranked as a supercohort under the subclass Theriiformes:

Class Mammalia

  • Subclass Theriiformes: live-bearing mammals and their prehistoric relatives

Another classification proposed by Luo et al. (2002)[9] does not assign any rank to the taxonomic levels, but uses a purely cladistic system instead.

See also

References

  1. ^ ITIS Standard Report Page: Theria
  2. ^ Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. "Subclass Theria". Animal Diversity Web.CS1 maint: multiple names: authors list (link)
  3. ^ 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. doi:10.1073/pnas.1417000112. PMC 4321253. PMID 25605903.
  4. ^ Ancient “genomic parasites” spurred evolution of pregnancy in mammals
  5. ^ 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.
  6. ^ 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.
  7. ^ Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. 2000. Mammalogy: Fourth Edition. Saunders College Publishing, 565 pp. ISBN 0-03-025034-X
  8. ^ 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
  9. ^ 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

Dryolestes

Dryolestes is an extinct genus of Late Jurassic mammal from the Morrison Formation and the Alcobaça Formation of Portugal.

Present in stratigraphic zones 2, 5, and 6.

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.

Holotheria

Holotheria are a diverse group of mammals that are descendants of the last common ancestor of Kuehneotherium and Theria (the group that includes marsupials and placental mammals).

List of mammals of Samoa

This is a list of the mammal species recorded in Samoa. There are nine mammal species in Samoa, of which one is endangered and two are vulnerable.

Prototheria

Prototheria (; from Greek πρώτος, prōtos, first, + θήρ, thēr, wild animal) is the subclass to which the orders Monotremata, Morganucodonta, Docodonta, Triconodonta and Multituberculata formerly belong.

Most of the animals in this group are extinct. The egg-laying monotremes are known from fossils of the Cretaceous and Cenozoic periods; they are represented today by the platypus and several species of echidna.

The names Prototheria, Metatheria, and Eutheria (meaning "first beasts", "changed beasts", and "true beasts", respectively) refer to the three mammalian groupings of which we have living representatives. Each of the three may be defined as a total clade containing a living crown-group (respectively the Monotremata, Marsupialia and Placentalia) plus any fossil species which are more closely related to that crown-group than to any other living animals.

The threefold division of living mammals into monotremes, marsupials and placentals was already well established when Thomas Huxley proposed the names Metatheria and Eutheria to incorporate the two latter groups in 1880. Initially treated as subclasses, Metatheria and Eutheria are by convention now grouped as infraclasses of the subclass Theria, and in more recent proposals have been demoted further (to cohorts or even magnorders), as cladistic reappraisals of the relationships between living and fossil mammals have suggested that the Theria itself should be reduced in rank.Prototheria, on the other hand, was generally recognised as a subclass until quite recently, on the basis of a hypothesis which defined the group by two supposed synapomorphies: (1) formation of the side wall of the braincase from a bone called the anterior lamina, contrasting with the alisphenoid in therians; and (2) a linear alignment of molar cusps, contrasting with a triangular arrangement in therians. These characters appeared to unite monotremes with a range of Mesozoic fossil orders (Morganucodonta, Docodonta, Triconodonta and Multituberculata) in a broader clade for which the name Prototheria was retained, and of which monotremes were thought to be only the last surviving branch.The evidence which was held to support this grouping is now universally discounted. In the first place, examination of embryos has revealed that the development of the braincase wall is essentially identical in therians and in 'prototherians': the anterior lamina simply fuses with the alisphenoid in therians, and therefore the 'prototherian' condition of the braincase wall is primitive for all mammals while the therian condition can be derived from it. Additionally, the linear alignment of molar cusps is also primitive for all mammals. Therefore, neither of these states can supply a uniquely shared derived character which would support a 'prototherian' grouping of orders in contradistinction to Theria.In a further reappraisal, the molars of embryonic and fossil monotremes (living monotreme adults are toothless) appear to demonstrate an ancestral pattern of cusps which is similar to the triangular arrangement observed in therians. Some peculiarities of this dentition support an alternative grouping of monotremes with certain recently discovered fossil forms into a proposed new clade known as the Australosphenida, and also suggest that the triangular array of cusps may have evolved independently in australosphenidans and therians.The Australosphenida hypothesis remains controversial, and some taxonomists (e.g. McKenna & Bell 1997) prefer to maintain the name Prototheria as a fitting contrast to the other group of living mammals, the Theria. In theory, the Prototheria is taxonomically redundant, since Monotremata is currently the only order which can still be confidently included, but its retention might be justified if new fossil evidence, or a re-examination of known fossils, enables extinct relatives of the monotremes to be identified and placed within a wider grouping.

Pseudotribos

Pseudotribos ("false chewing") is an extinct genus of mammal that lived in Northern China during the Middle Jurassic some 165 million years ago, possibly more closely related to monotremes than to theria (placental and marsupial mammals), although other studies indicate that these shuotheres are closer to therians than to monotremes. The only known specimen was found in the Daohugou Bed in Inner Mongolia (41.3°N 119.2°E / 41.3; 119.2: paleocoordinates 42.6°N 122.4°E / 42.6; 122.4).

Theria primaria

Theria primaria, the early moth, is a moth of the family Geometridae. It is found throughout Western Europe and the South Caucasus.

The wingspan is 32–37 mm (1.3–1.5 in) and the forewings are 14–17 mm (0.55–0.67 in) long. The ground colour of the forewings is reddish brown. The male subterminal and antemedial lines are slightly wavy with the areas between these lines usually being a darker brown than the ground colour. The forewing apex is rounded and there is a small discal spot towards the costal edge. The hindwings are pale whitish brown with a tiny discal spot. Females have short wings (60% of the length of the abdomen."The male may be known at once by the large discal spot of the forewing and the 2 crenulate dark lines, white-edged on the reverse sides. The rudimentary wings of the female have the apex acute, the forewing bears 2 approximated dark lines, the intervening space often darkened into a band. — ab. ibicaria H.-Sch. is darker, with the lines obsolete." The moth flies from January to February [1].

The larva feeds on hawthorn and blackthorn.

Theria rupicapraria

Theria rupicapraria is a moth of the family Geometridae. It is found throughout in Europe and the South Caucasus.

The wingspan is 28–30 mm for males. Females have reduced wings. Adults are on wing from January to April. There is one generation per year.

The larvae feed on Crataegus and Prunus spinosa. Larvae can be found in June. It overwinters as a pupa.

Therian

Therian may refer to:

In taxonomy, a member of the mammalian subclass Theria, consisting of marsupial and placental mammals

A member of the contemporary subculture of therianthropy, based on a spiritual or psychological identification, or both, with animals

Tribosphenida

Tribosphenida is a group (infralegion) of mammals that includes the ancestor of Hypomylos, Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants). Its current definition is more or less synonymous with Boreosphenida.

Extant mammal orders
Yinotheria
Theria

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