Placental mammals (infraclass Placentalia /plæsənˈteɪliə/) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer, considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less-developed young, which are then nurtured for a period inside the mother's pouch. Placentalia represents the only living group within Eutheria, which contains all mammals that are more closely related to placentals than they are to marsupials.
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👉 Placental mammals in the context of Pantolestidae
Pantolestidae ("all robbers") is an extinct paraphyletic family of placental mammals from extinct order Pantolesta, that lived in North America, Asia and Europe from the early Paleocene to middle Oligocene. They first appear in North America, whence they spread to Europe and Asia.
Placental mammals in the context of Excretion
Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell. For example, placental mammals expel urine from the bladder through the urethra, which is part of the excretory system. Unicellular organisms discharge waste products directly through the surface of the cell.
During life activities such as cellular respiration, several chemical reactions take place in the body. These are known as metabolism. These chemical reactions produce waste products such as carbon dioxide, water, salts, urea and uric acid. Accumulation of these wastes beyond a level inside the body is harmful to the body. The excretory organs remove these wastes. This process of removal of metabolic waste from the body is known as excretion.
Placental mammals in the context of Bladder
The bladder (from Old English blædre 'bladder, blister, pimple') is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distensible organ that sits on the pelvic floor. The typical adult human bladder will hold between 300 and 500 ml (10 and 17 fl oz) before the urge to empty occurs, but can hold considerably more.
The Latin phrase for "urinary bladder" is vesica urinaria, and the term vesical or prefix vesico- appear in connection with associated structures such as vesical veins. The modern Latin word for "bladder" – cystis – appears in associated terms such as cystitis (inflammation of the bladder).
Placental mammals in the context of Os clitoris
The os clitoridis (also called the os clitoris, clitoral bone or baubellum; pl.: baubella) is a bone inside the clitoris of many placental mammals. It is absent from the human clitoris, but present in the clitoris of some primates, such as ring-tailed lemurs and non-human great apes. However, in the latter case, the bone is greatly reduced in size. It is homologous to the baculum in male mammals.
The structure is more evolutionarily labile than the baculum, exhibiting both more inherent variability and more gains and losses over time, which has been interpreted as evidence for its non-functionality.
Placental mammals in the context of Afrotheria
Afrotheria (/ˌæfrəˈθɪəriə/; from Latin Afro- "of Africa" + theria "wild beast") is a superorder of placental mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also known as sengis), otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times due to genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.
Because Africa was isolated by water, Laurasian groups of mammals such as insectivores, rodents, lagomorphs, carnivorans and ungulates could not reach Africa for much of the early to mid-Cenozoic. Instead, the niches occupied by those groups on the northern continents were filled by various groups of afrotheres via the process of convergent evolution. The small insectivorous afrotheres such as elephant shrews, golden moles, and tenrecs filled the niches of insectivores, the hyraxes filled the roles of rodents and lagomorphs, the aardvarks filled the roles of various medium size ant-eating mammals (anteaters, armadillos, pangolins, echidnas, numbats, etc.) found on other continents throughout the Cenozoic, and proboscideans (elephants and their relatives) filled the roles of large herbivores such as hippos, camels, rhinos, and tapirs. The sirenians developed aquatic body plans and started spreading to other parts of the world by water (evolving convergently with the other groups of marine mammals such as cetaceans and pinnipeds). In addition to their similarity with Laurasian mammals in North America, Europe, and Asia, many afrotheres also exhibit convergent evolution with groups of mammals that evolved and lived exclusively in South America, which was also an island continent for much of the Cenozoic.