Immunology

Why are so many people getting a tick-borne meat allergy?

It is early morning in early summer, and I am tracing my way through the woods of central North Carolina, steering cautiously around S-curves and braking hard when what looks like a small rise turns into a narrow bridge. ...

Diseases, Conditions, Syndromes

Spleen microbes of wild animals change with tick-borne illness

Anaplasmosis, a tick-borne febrile disease, can be carried by wild mammals before being transmitted to humans through a tick bite. Now, researchers reporting in PLOS Neglected Tropical Diseases have found that Anaplasma bacteria ...

Diseases, Conditions, Syndromes

Plague kills 19 in Madagascar

An outbreak of plague in Madagascar has killed 19 people and may have infected 85 others in just two months, the Indian Ocean island nation's health minister said Thursday.

Medical research

New research suggests appendix may have important function

The human appendix, a narrow pouch that projects off the cecum in the digestive system, has a notorious reputation for its tendency to become inflamed (appendicitis), often resulting in surgical removal. Although it is widely ...

Health

Mercury exposure in Canada's northern indigenous communities

Mercury exposure is common in communities in Canada's north, especially in indigenous peoples who consume fish and other wild food with high mercury content, yet current clinical guidelines are not adequate for this population. ...

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Mammal

Mammals (formally Mammalia) are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.

Mammals are divided into three main categories depending how they are born. These categories are, monotremes, marsupials and placentals. Except for the five species of monotremes (which lay eggs), all mammal species give birth to live young. Most mammals also possess specialized teeth, and the largest group of mammals, the placentals, use a placenta during gestation. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart.

There are approximately 5,400 species of mammals, distributed in about 1,200 genera, 153 families, and 29 orders (though this varies by classification scheme). Mammals range in size from the 30–40-millimetre (1.2–1.6 in) Bumblebee Bat to the 33-metre (110 ft) Blue Whale.

Mammals are divided into two subclasses, the prototheria, which includes the oviparous monotremes, and the theria, which includes the placentals and live-bearing marsupials. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders include the Carnivora (dogs, cats, weasels, bears, seals, and their relatives), the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Primates to which the human species belongs. The relative size of these latter three orders differs according to the classification scheme and definitions used by various authors.

Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals). This means that some extinct groups of "mammals" are not members of the crown group Mammalia, even though most of them have all the characteristics that traditionally would have classified them as mammals. These "mammals" are now usually placed in the unranked clade Mammaliaformes.

The mammalian line of descent diverged from an amniote line at the end of the Carboniferous period. One line of amniotes would lead to reptiles, while the other would lead to synapsids, including mammals. The first true mammals appeared in the Triassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.

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