The origin and evolution of mammals / Происхождение и эволюция млекопитающих

There are about 4,600 species of animals today that are called mammals because, despite an astonishing diversity of form and habitat, they all share a long list of characters not found in any other organisms, such as the presence of mammary glands, the single bone in the lower jaw, and the neocortex of the forebrain. This makes them unambiguously distinct from their closest living relatives, and their unique characters together define a monophyletic taxon, the class Mammalia. Three subgroups are readily distinguished amongst the living mammals. The Monotremata are the egg-laying mammals of Australasia, consisting only of two species of echidna and a single platypus species; for all their primitive reproductive biology, monotremes are fully mammalian in their general structure and biology. The Marsupialia, or Metatheria are the pouched mammals, whose approximately 260 species dominate the mammalian fauna of Australia, and also occur as part of the indigenous fauna of the Americas. By far the largest  roup of living mammals are the Placentalia, or Eutheria with about 4,350 species divided into usually eighteen recent orders. <...>