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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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(vertebrate zoology)
An infraclass of therian mammals including all living forms except the monotremes and marsupials.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Robinson, "LINE-1 distribution in Afrotheria and Xenarthra: implications for understanding the evolution of LINE-1 in eutherian genomes," Chromosoma, vol.
A series of knockout mouse experiments on Sirh genes has been carried out in an effort to elucidate their biological functions in development, reproduction, growth and behavior, as well as their presumed contribution to eutherian evolution.
(1990) encountered similarities in the distribution and relative frequency of endocrine cells in the duodenum of eight marsupial species as well when compared to eutherian mammals, showing no difference between marsupials, herbivores, omnivores or carnivores.
He covers the late Cretaceous nonavian dinosaur record, in the shadow of nonavian dinosaurs, in search of the most ancient Eutherian ancestors of placental mammals, patterns and causes of extinction at the K/T boundary, and when and whence mammals after the impact.
The evolutionary trend in most mammalian species has been a reduction in the number of teeth from the primitive eutherian ("placental") dental formula of 3-1-4-3/3-1-4-3 = 44 teeth.
Herein, we report the results of a comparative genomic analyses of the [beta]-globin gene in 11 different taxa; nine eutherian [Homo sapiens (human), Macaca mulatta (rhesus monkey), Pan troglodytes (chimpanzee), Rattus norvegicus (mouse), Mus musculus (rat), Canis familiaris (dog), Bos taurus (cow), Equus caballus (horse), Oryctolagus cuniculus (rabbit)], one dinosaurian (avian) Gallus gallus (chicken) and a neopterygii (marine) Danio rerio (fish), describing fundamental similarities and differences among taxa to enable better evolutionary understanding of functional [beta]-globin gene (Fig.
Significance of the equatorial segment of the acrosome of the spermatozoon in eutherian mammals.
Eutherian mammals have an XY system where SRY on the Y determines maleness, so XXY is male and XO is female.
Eutherian mammals like mice and humans protect their progeny for lengthy periods in an inner womb prior to giving birth.
Morton SR, Recher HF, Thompson SD, Braithwaite RW (1982) Comments on the Relative Advantages of Marsupial and Eutherian Reproduction.
Most of the information presented in this book pertains to the eutherian mammals.