A dog’s heart beats 70 to 120 times a minute, compared to a
human’s which beats 70 to 80 times a minute. The largest breed
of dog is the Irish Wolfhound. The Chihuahua is the smallest,
while the St. Bernard and Mastiff are among the heaviest. Dogs
descend from a weasel-sized mammal called Miacis which was a
tree-dwelling carnivore that existed over 40 million years ago
in the North America and Europe regions. There are about 700
types of pure breed dogs. A dog's sense of smell is about 1000
times better than a person's. A one-year-old dog is as
physically mature as a 15 year-old human.