 Mammals are the vertebrates within the class mammalidae, the clade of endothermic antihodes distinguished from reptiles including birds by the possession of a meal cortex, a region of the brain hair, three middle ear bones, and mammary glands. Females of all mammal species nurse their young with milk, secreted from the mammary glands. Mammals include the largest animal on the planet, the blue whale. The basic body type is a terrestrial quadruped, but some mammals are adapted for life at sea, in the air, in trees, underground or on two legs. The largest group of mammals, the placentals, have a placenta, which enables the feeding of the fetus during gel station. Mammals range in size from the 30 to 40 mm 1.2 to 1.6 and bubbly bat to the 30 m 98 feet blue whale. With the exception of the five species of monitoring egg-laying mammals all modern mammals give birth to live young. Most mammals, including the six most species rich orders, belong to the placental group. And the largest orders are the rodents, bats and sari co-morphal shrews and allies. The next three biggest orders, depending on the biological classification scheme used, are the primate sapes and monkeys, the sirtar, the odactyla whales and even toad ungulates and the carnivore cats, dogs, seals, and allies. Monitoring mammals are divided into the yeenote area platypus and echinus and theria forms all other mammals. There are around 50 for 50 species of mammal, depending on which authority is cited. In some classifications, extant mammals are divided into subclasses, the prototheria, that is, the order monotrimidae, and the theria, or the infraclass of metathariate and eutheria. The marsupials constitute the crown group of the metathariate, and include all living metathariate ants as well as many extinct ones, the placentals are the crown group of the eutheria. While mammal classification at the family level has been relatively stable, several contending classifications regarding the higher levels subclass, infraclass and order, especially of the marsupials appearing contemporaneous literature. Much of the changes reflect the advances of clodistic analysis and molecular genetics. Findings from molecular genetics, for example, have prompted adopting new groups, such as the aphrothariae, and abandoning traditional groups, such as the insectivorae. The mammals represent the only livings in Acida, which together with the sorrow seed form the amnioclade. The earliest in Acida mammalian ancestors were Sphenicodontpolycosaurus, a group that produced the non-mammalian dimetra. At the end of the Carboniferous Period, this group diverged from the sorrow seed line that led to today's reptiles and birds. The line following the stem groups Sphenicodontius split off several diverse groups of non-mammalians in absids sometimes referred to as mammal-like reptiles before giving rise to the proto-nammals paraxidae in the early Mesozoic Era. The modern mammalian orders arose in the Paleo-Gene and Neil-Gene periods of the Mesozoic Era, after the extinction of non-avian dinosaurs, and have been among the dominant terrestrial animal groups from 66 million years ago to the present. Most mammals are intelligent, with some possessing large brains, self-awareness and tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent marking, alarm signals, singing, and echolocation. Mammals can organize themselves in deficient fusion societies, headrooms, and hierarchies, but can also be solitary and territorial. Most mammals are polygenous, but some can be monogamous or polyandrous. In human culture, domesticated mammals played a major role in the Neolithic Revolution, causing farming to replace hunting and gathering, and leading to a major restructuring of human societies with the first civilizations. They provided, and continue to provide, power for transport and agriculture, as well as various commodities such as meat, dairy products, wool, and leather. Mammals are hunted or raised for sport, and are used as model organisms in science. Mammals have been depicted in arts since Paleolithic times, and appear in literature, film, mythology, and religion. The thought nation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, though there are efforts to combat this.