What is a dog

The dog (Canis lupus familiaris) is a domesticated subspecies of the gray wolf, a mammal of the Canidae family of the order Carnivora. The term can also be used more generally to encompass any member of the biological family Canidae, the Genus Caninae (also called "true dogs"). When referring to Canis lupus familiaris, the term is used to specify both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history. There are estimated to be 400 million dogs in the world.The dog has developed into hundreds of varied breeds. Height measured to the withers ranges from a few inches in the Chihuahua to a few feet in the Irish Wolfhound; color varies from white through grays (usually called blue) to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be very short to many centimeters long, from coarse hair to something akin to wool, straight or curly, or smooth. It is common for most breeds to shed this coat, but non-shedding breeds are also popular.

The Scientific Classification of dog :
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Canis
Species: C. lupus

Biology
Domestic dogs come in many shapes and sizes because they have been selectively bred for millenia for various behaviors, sensory capabilities, and physical attributes. Their morphology, although highly modified, is based on that of their wild ancestors, gray wolves. Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wristbones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Dogs are more variable in size than any other domesticated animal.[citation needed] The smallest known dog was a Yorkshire Terrier, who stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.75 in) in length along the head-and-body, and weighed only 113 grams (4 ounces). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lbs) and was 250 cm (8.2 feet) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.2 in) at the shoulder.