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Related to placental mammal: marsupial, Carnivora


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 ?
The study counters prior research, based solely on fossil evidence, which theorized this "mother of all placental mammals" arose after the dinosaurs died out.
Placental mammals are the largest branch of the mammalian family tree, with more than 5,100 living species.
The second clan comprised fossils from the Northern Hemisphere and the placental mammals and marsupials.
Studies with a scanning electron microscope and a laser scanning microscope revealed that the microstructure of the tooth's enamel also resembles that of a placental mammal.
Placental Mammals are Viviparous--They Bear Live Young
Devor, "Placenta-specific protein 1 (PLAC1): a key element in the emergence and success of placental mammals," Scientific World Journal, 2013.
This gene, ZBED6, was previously unknown, but the research team soon discovered that it was unique to the placental mammals, including us humans.
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.
of Athens) present a long-awaited, state-of-the-art reference book about fossil insular placental mammals worldwide.
Researchers found brain size in marsupials and placental mammals correlated with length of maternal care.
This had to occur after the time of the common ancestor of mammals and birds/reptiles (310 million years ago), and before the time of the common ancestor of placental mammals and marsupials (eutherians; 145 million years ago), because both placental mammals and marsupials have XY sex determination with SRY determining maleness.
This applies to all convergencies such as those between marsupial and placental mammals as well as between African and American succulent plants.