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 Tasmanian devil
), also referred to simply as 'the devil', is a carnivorous marsupial
now found in the wild only in the Australian island state
. The Tasmanian devil is the only extant member of the genus Sarcophilus
. The size of a small dog, but stocky and muscular, the Tasmanian devil is now the largest carnivorous marsupial in the world (after the recent extinction
of the thylacine
in 1936). It is characterised by its black fur, offensive odour when stressed, extremely loud and disturbing screech, and viciousness when feeding. It is known to both hunt prey and scavenge carrion
and although it is usually solitary, it sometimes eats with other devils. The Tasmanian devil became extirpated
on the Australian mainland about 400 years before European settlement
in 1788. Because they were seen as a threat to livestock
in Tasmania, devils were hunted until 1941, when they became officially protected. Since the late 1990s devil facial tumour disease
has reduced the devil population significantly and now threatens the survival of the species, which may soon be listed as endangered
. Programs are currently being undertaken by the Tasmanian government
to reduce the impact of the disease.