Eucerata

A subclass of Mammalia

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Eutheria (scientific name: Eutheria) is the highest class of vertebrates with the most complex body structure and functional behavior (brain structure has corpus callosum). There are 20 orders of animals in this subclass, with a wide variety, accounting for about 95% of the existing mammals. Viviparity , with a real placenta.

Chinese name: Eucerata
Latin name: Eutheria
Alias: Placenta
circles: Animal kingdom

door: Chordate （Chordata）
Yamen: Vertebrate （Vertebrata）
Outline: Mammalia （Mammalia）
Subclass: Eutheria

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Distribution range

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Almost all over the world except Antarctica, the center of the Arctic and individual islands.

brief introduction

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Zodiac is also called Placenta animal There are 20 orders with a wide variety, accounting for about 95% of the existing mammals, which are distributed in all corners of the world. The reproduction method of Euzoa is viviparity, and it has a real placenta. The embryo develops in the mother's uterus for a long time. It absorbs the mother's nutrition through the placenta, and the baby is fully developed. After birth, it can suck its own milk. The mother animal has developed mammary glands and nipples. The cerebral cortex is developed, and the temperature is high and constant.^[1]

form

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Zodiac camel (5 sheets)

Vertebrates with full body hair (except for a few species), fast movement and constant temperature are the most sophisticated group of vertebrates with the most complex body structure and functional behavior. Body hair; temperature Constancy; Fetal birth (except monotreme) and lactation; The left and right chambers of the heart are completely separated, and the left ventricle pumps blood to all parts of the body through the left arterial arch; Cranial enlargement and brain volume increase; The middle ear has three ossicles; The mandible is composed of one tooth bone, which is articulating with the skull in the form of tooth squamous bone; The teeth differentiate into Incisor 、 Canine tooth and Buccal tooth ； There are 7 cervical vertebrae, and the first and second cervical vertebrae differentiate into the annulus and axis.

Main features

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Viviparity , with a real placenta. embryo inutero uterus The internal development time is long, and the maternal nutrition is absorbed through the placenta Cub Fully developed, able to suck milk by oneself. breast Developed with papilla 。 brain cortex Developed, two major hemisphere Between corpus callosum to be connected. The body temperature is high and constant, Mastoid tooth And permanent tooth The replacement is obvious. Shoulder strap is single Scapula ， coracoid Degenerated into suprascapular Coracoid process 。 None Cloaca ， Intestinal canal With the anal opening alone, excretion And Genital canal Import Cloacal sinus , with Cloacal orifice Open the body.^[2]

Eucerata (5 sheets)

origin

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In the Mesozoic Jurassic period, the molar tooth tips of the three tuberous teeth seen in this period have changed from the straight arrangement of the three cone teeth to the triangular arrangement. Three branches have evolved from the trinododont, namely, tridentate mammals, contradentate mammals and ancient mammals, of which the first two lived until the end of Jurassic and the beginning of Cretaceous, and the third branch of ancient mammals developed vigorously. The molars of ancient mammals were also arranged in a triangle, but there was a "lower heel projection" with two tooth tips behind the mandibular molars. Ancient beasts are the ancestors of metazoa and euzoa.^[3]