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 Labrador Retriever
for short), is one of several kinds of retriever
, a type of gun dog
. The Labrador is considered the most popular breed
(by registered ownership) in the world, and is by a large margin the most popular breed by registration in the United States
) the United Kingdom
, It is also the most popular breed of assistance dog
in the United States, Australia
, and many other countries, as well as being widely used by police and other official bodies for their detection and working abilities. They are exceptionally affable, gentle, intelligent, energetic and good natured, and Labradors are generally considered good companions for people of all ages (including a high level of patience and tolerance for children
, making them both excellent companions and working dogs
. Although somewhat boisterous if untrained, Labrador Retrievers respond well to praise and positive attention, and are considerably "food and fun" oriented.These dogs are as well loyal and great with little children. They may be used in shows. With training, the Lab is one of the most dependable, obedient and multi-talented breeds in the world.