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Mammals (class Mammalia) are vertebrate animals characterized by the presence of sweat glands, including milk producing sweat glands, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in the brain. Mammals, other than the monotremes, give birth to live young instead of laying eggs. They also possess specialized teeth and use a placenta in the ontogeny. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass approximately 5,400 species, ranging in size from the Bumblebee Bat, (30-40mm), to the Blue Whale, (33,000mm), distributed in about 1,200 genera, 153 families, and 29 orders, though this varies by classification scheme. Most mammals belong to the placental group. The four largest orders within the placental mammals are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), Carnivora (dogs, cats, bears, and other mammals that primarily eat meat), and Cetartiodactyla (including numerous herbivore species, such as deer, sheep, goats, and buffalos, plus whales). 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 the sauropsid line at the end of the Carboniferous period. The sauropsids would evolve into modern-day reptiles and birds, while the synapsid branch led to mammals. The first true mammals appeared in the Jurassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period. The cougar (Puma concolor), also puma, mountain lion, or panther, is a mammal of the Felidae family, native to the Americas. This large, solitary cat has the greatest range of any wild terrestrial mammal in the Western Hemisphere, extending from Yukon in Canada to the southern Andes of South America. An adaptable, generalist species, the cougar is found in every major New World habitat type. It is the second heaviest cat in the New World, after the jaguar, and the fourth heaviest in the world, after the tiger, lion, and jaguar, although it is most closely related to smaller felines. A capable stalk-and-ambush predator, the cougar pursues a wide variety of prey. Primary food sources include ungulates such as deer and bighorn sheep, as well as domestic cattle, horses, and sheep, particularly in the northern part of its range, but it hunts species as small as insects and rodents. It prefers habitats with dense underbrush and rocky areas for stalking, but it can live in open areas. Cougars are known to kill at least one deer sized animal per week, more in warmer climates; unlike bears, they do not like spoiled meat. The cougar is territorial and persists at low population densities. Individual territory sizes depend on terrain, vegetation, and abundance of prey. While it is a large predator, it is not always the dominant species in its range, as when it competes for prey with animals such as the gray wolf, black bear, and the grizzly bear. It is a reclusive cat and usually avoids people. Attacks on humans remain rare, despite a recent increase in frequency. Opposable 'thumb' on male polydactyl cat. ...that a polydactyl cat (pictured) is a cat that has more than the usual number of toes on one or all of its paws? ...that Unsinkable Sam was a ship's cat of both the Kriegsmarine and Royal Navy during the Second World War who survived the sinking of all three ships on which he served? ...that Able Seaman Just Nuisance is the only dog to have been officially enlisted in the Royal Navy? ...that the Moscow Water Dog, developed as a water rescue dog, preferred to bite drowning people instead of saving them? ...from its discovery by John Edward Gray in 1850 until a re-assessment in 1981, the Clymene Dolphin was regarded as sub-species of the Spinner Dolphin. ...the Australian Snubfin Dolphin (Orcaella heinsohni) is a recently recognised species of dolphin first described in 2005. The Harbor seal or Common seal (Phoca vitulina) is a true seal of the Northern Hemisphere. Having the widest range of all pinnipeds, Harbor seals are found in coastal waters of the northern Atlantic and Pacific Oceans as well as those of the Baltic and North Seas. Monotremata Didelphimorphia Paucituberculata Microbiotheria Notoryctemorphia Dasyuromorphia Peramelemorphia Diprotodontia Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia Cingulata Pilosa Scandentia Dermoptera Primates Rodentia Lagomorpha Erinaceomorpha Soricomorpha Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Biology Tree of Life Prokaryotes and Protists Plants Arthropods Cephalopods Gastropods Fishes Amphibians and Reptiles Birds Mammals WikiProject Dogs WikiProject Dog breeds WikiProject Rodents WikiProject Cats WikiProject Equine WikiProject Horse breeds WikiProject Cetaceans WikiProject Primates WikiProject Monotremes and Marsupials Viruses A complete list of scientific WikiProjects can be found here. See also Wikispecies, a Wikimedia project dedicated to classification of biological species. Articles needing attention Biology pages needing attention (cleanup, expansion, wikification, expert needed, etc.) Help Wikipedia by uploading required images Help Wikipedia by creating pages or redirects Help Wikipedia by expanding mammal-related stub articles. Biology • Agriculture and Agronomy • Animals  • Arthropods • Amphibians and Reptiles • Biotechnology • Birds • Cats • Cetaceans • Dinosaurs • Dogs • Extinct and Endangered Species • Evolutionary biology • Fish • Marine life • Medicine • Metabolism • Mind and Brain • Molecular and Cellular Biology • Neuroscience • Plants • Primates • Sharks • Turtles What are portals? List of portals Featured portals