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Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the
clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic—that is, composed of a common ancestor and all its lineal descendants - on a phylogenetic tree. R ...
consisting of all therian mammals that are more closely related to
placentals Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mot ...
than to
marsupials Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a pouch. Well-kn ...
. Eutherians are distinguished from noneutherians by various
phenotypic trait A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two.Lawrence, Elea ...
s of the feet, ankles, jaws and teeth. All extant eutherians lack
epipubic bone hind legs. Epipubic bones labeled as 10 Image:Paris - Université Pierre-et-Marie-Curie - Macropus rufogriseus 17.jpg">Skeleton of pelvis">pelvic_bones_of_modern_marsupials_and_most_non-placental_fossil_mammals:_Multituberculata.html" style="t ...
s, which are present in all other living mammals (marsupials and
monotreme Monotremes are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). The monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and ot ...
s). This allows for expansion of the abdomen during pregnancy. The oldest-known eutherian species is ''
Juramaia sinensis ''Juramaia'' is an extinct genus of very basal eutherian mammal known from the Late Jurassic (Oxfordian stage) deposits of western Liaoning, China. It is a small shrew-like mammal with a body length of approximately 70–100 mm, making it sim ...
'', dated at from the early
Late Jurassic The Late Jurassic is the third epoch of the Jurassic period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name "Ma ...
( Oxfordian) of China. Eutheria was named in 1872 by
Theodore Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural history. ...
; in 1880
Thomas Henry Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist specialising in comparative anatomy. He is known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stories regard ...

Thomas Henry Huxley
defined it to encompass a more broadly defined group than Placentalia.


Characteristics

Distinguishing features are: *an enlarged
malleolus A malleolus is the bony prominence on each side of the human ankle. Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg. The medial malleolus is the prominenc ...
("little hammer") at the bottom of the
tibia The tibia (plural tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the ...
, the larger of the two shin bones *the
joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw-Hill Connect. Webp.274/ref> They are construc ...

joint
between the first
metatarsal bone The metatarsal bones, or metatarsus are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial ...
and the entocuneiform bone (the innermost of the three
cuneiform bones There are three cuneiform ("wedge-shaped") bones in the human foot: * the first or medial cuneiform * the second or intermediate cuneiform, also known as the middle cuneiform * the third or lateral cuneiform They are located between the navicul ...
) in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones—in metatherians these joints are level with each other *various features of jaws and teeth


Evolutionary history

Eutheria contains several
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and rec ...
genera Genus (plural genera) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...
as well as larger groups, many with complicated taxonomic histories still not fully understood. Members of the
Adapisoriculidae Adapisoriculidae is an extinct family of eutherian mammals present during the Paleocene and possibly Cretaceous. They were once thought to be members of the order Erinaceomorpha, closely related to the hedgehog family (Erinaceidae), because of the ...
,
Cimolesta Cimolesta is an extinct order of non-placental eutherian mammals. Cimolestans had a wide variety of body shapes, dentition and lifestyles, though the majority of them were small to medium-sized general mammals that bore superficial resemblances to r ...
and
Leptictida Leptictida (''leptos iktis'' "small/slender weasel") is a possibly invalid extinct order of placental mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires (rodents, prim ...
have been previously placed within the out-dated placental group
Insectivora The order Insectivora (from Latin ''insectum'' "insect" and ''vorare'' "to eat") is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order Eulipotyphla, within ...
, while Zhelestids have been considered primitive
ungulate Ungulates (pronounced ) are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, ...
s. However, more recent studies have suggested these enigmatic taxa represent
stem group upright=1.5, Two distinct crown groups (in red) are illustrated, connected by an ancestor (black circle). The two groups form a larger crown group (lilac). In phylogenetics, the crown group or crown assemblage is a collection of species, composed ...
eutherians, more basal to Placentalia. The weakly favoured cladogram favours Boreoeuthearia as a basal eutherian clade as sister to the Atlantogenata.


References

{{Taxonbar, from=Q17092469
Mammal taxonomy{{Catmain, Mammal classification .taxonomy . ...
Oxfordian first appearances Extant Late Jurassic first appearances