Eutheria

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Related to Eutherians: metatherians, prototherians

Eutheria

A higher-level taxon that includes all mammals except monotremes and marsupials. Eutheria (Placentalia) is variously ranked as an infraclass or cohort within Mammalia. Eutheria includes over 4000 living species arranged in 18 orders; another 12 orders are known only from fossils. An ecologically diverse group, Eutheria includes primates, insectivores, bats, rodents, carnivores, elephants, ungulates, and whales. Like other mammals, eutherians are generally fur-covered and produce milk to nourish their young. In part because they can make their own body heat and regulate their body temperature, eutherians are widely distributed over most continents and occur in all oceans.

Eutherians, often called placental mammals, have a unique reproductive system in which unborn young are nourished for an extended period via a placenta. This system permits retention of the young in the protective environment of the uterus during most of early development. Fetal survival rates are high under most conditions. Young are born in a relatively advanced state of development and are never sheltered in a pouch after birth. Gestation time ranges from 20 days (for example, shrews and hamsters) to 22 months (elephants). Many eutherians have only one or two young per pregnancy, but as many as 20 offspring may be produced at a single birth in some species.

Eutherians range in size from insectivores and bats that weigh only a few grams to blue whales that can weigh over 190,000 kg (420,000 lb). All have a relatively large brain and exhibit complex behavior, with many living in social groups. Eutherians exhibit more variation in ecology than any other group of vertebrates, and these differences are reflected in their morphological specializations.

The fossil record of Eutheria extends back at least into the Cretaceous Period. Several differences in the skull and dentition distinguish fossil eutherians from early members of other mammal lineages (for example, marsupials). The earliest eutherians were apparently small, nocturnal mammals that may have resembled some modern insectivores. Although Cretaceous eutherians are known from most continents, diversification of the modern orders apparently did not occur until the Paleocene and Eocene. See Cetacea, Chiroptera, Mammalia, Theria

Eutheria

 

an infraclass of viviparous mammals having the highest organization and the greatest ecological and morphological diversity. The brain characteristically has large, highly developed hemispheres, which are connected by means of the corpus callosum. Embryonic development involves the formation of a placenta. The marsupial bones characteristic of marsupials, the second infraclass of viviparous mammals, are absent. The dental formula is:

The Eutheria include 14 extinct and 17 extant orders. They have been traced to the Early Cretaceous.

Eutheria

[yü′thir·ē·ə]
(vertebrate zoology)
An infraclass of therian mammals including all living forms except the monotremes and marsupials.
References in periodicals archive ?
It is known that ENV genes have also become essential endogenous genes in a lineage-specific manner in the eutherians and marsupials, e.g.
(44,45) Among the eutherians, placental morphology have substantially diverged.
This means that the platypus XY evolved independently of the eutherian XY and determines sex in a different, still unknown, way.
The platypus XY probably evolved independently of the eutherian XY.
These mutations added one base (at two sites) and two bases (at one site) to the original sequence, and are found at the identical positions in all the Eutherian species for which sequences have been obtained.
Further, even under the best conditions, it is quite difficult to correlate systems when animals differ significantly, such as occurs in comparisons between eutherians and metatherians.
In marsupials the period examined represents the time immediately prior to birth (generally one to three days prenatal) and the early postnatal period (approximately the first quarter of "pouch" life) and in eutherians, the period is entirely intrauterine, spanning the onset of histogenesis through organogenesis.
Finally, the mammalian faunule of Lano is one of the richest hitherto discovered in Europe and provides data on the evolution of early eutherians (Gheerbrant and Astibia, 2012).
Mass-adjusted FMR, i.e., FMR divided by mass raised to the slope of the allometric equation for desert eutherian mammals, equaled 2.90 kJ[multiplied by][g.sup.0.786][multiplied by][d.sup.-1] and 2.85 kJ[multiplied by][g.sup.0.786][multiplied by][d.sup.-1] for summer and winter foxes, respectively.
At the time of both pregnancies I had two cats who, being themselves in possession of eutherian knowledge, were well aware that my body had embarked on a major project.
The present study reveals several interesting evolutionary observations on the HBB gene among the eutherian, dinosaurian and neopterygii taxa.
Jones, unpublished manuscript) and the dentine-enamel junction grows progressively towards the tip of the canine, crown height was measured from the junction of tooth with skull instead of the dentine-enamel junction as is used in eutherian carnivores (Van Valkenburgh and Ruff 1987).