Dogs (and wolves and foxes) are descended from a small, weasel-like mammal called Miacis which was a tree-dwelling creature and existed about 40 million years ago. Dogs, as we know them today, first appeared in Eurasia about 13,000 years ago, and were probably a direct descendant of a small, grey wolf (not from the type of jackal or jackal/wolf as previously thought). The dingo is not native to Australia but was introduced thousands of years ago by the first immigrants. Dogs were first domesticated by cavemen in the Palaeolithic age and gradually developed (or were bred) into the breeds known today.

The tallest dogs are the Great Dane and the Irish Wolfhound. The largest Great Dane stood at 103cm and an Irish Wolfhound 100cm.

The heaviest dog was a St. Bernard weighing 63.5kg. The smallest dogs are the Chihuahua, the Yorkshire Terrier and the Toy Poodle. A Yorkie once weighed in at only 283.5g.

Dogs have been used as guards, hunters, draught animals, eyes for the blind, drug and explosive detectors, rodent controllers- and even weapons! In Roman times and the Middle Ages, mastiffs wearing light armour, carrying spikes and pots of flaming sulphur and resin ran into battle against mounted knights. In World War II the Russians trained dogs to run suicide missions between the tracks of German tanks with mines strapped on their backs.

Dogs' hearing is very acute. They can register sounds of 35,000 vibrations a second (compared to our 20,000 and a cat's 25,000).

Dogs naturally have a wonderful sense of smell. They have many more sensory 'smelling' cells than a man's 5,000,000. A Dachshund has 125,000,000, a Fox Terrier 147,000,000 and an Alsation (often used as a 'sniffer' dog) has 220,000,000. Truffle hounds can find the fungus delicacy even when it's a foot underground.

The oldest reliable age recorded for a dog is 29 years, 5 months for a Queensland 'heeler' called Bluey in Victoria, Australia. The average dog lives to around 15 years of age.

Found Here http://www.ccc.govt.nz/animals/DogFacts.asp