The dog is a domesticated wolf, and its history must be traced through the ancestors of this carnivore. (It used to be thought that the jackal had contributed to the ancestry of the dog, but on morphological and behavioral grounds this is no longer tenable.) The forerunners of the wolf, such as Aelurodon, were present in North America during the late Miocene and early Pliocene, roughly 15 million to 10 million years ago, but they are not commonly found in Europe until the Villafranchian, the earliest stage of the Pleistocene about 2 million years ago. True wolves, however, appeared in Europe in the middle Plistocene, some 1 million years ago, but they are not recorded from the New World until some 700.000 years later.
In the Old World the earliest definite remains of the dog were found at a Mesolithic ( Middle Stone Age) site in Britain dated at 9500 B. P. (before the present) and in the Turkish site of Cayonu dated at 9000 B. P. Even earlier remains, however, have been found in North America at Jaguar Cave in Idaho. This site has been dated at approximately 10,500 B. P.
Identification of very early domestic dogs remains a complex task, and the results are always open to interpretation, but it is probable that the dog w as the first animal to be domesticated by man These early dogs resembled the present- day dingo, the feral dog of Australia.
Following domestication, selective breeding produced dogs of divergent forms. The ancient Egyptians, as early as the 5th millennium B. c. (about 7,000 years ago), had dogs of many distinctive breeds, including the forerunners of the greyhound, mastiff, and dachshund.
DOG DAYS is a term applied to the hottest season of the year. The term originated in ancient times, when what was usually the hottest season a period of about 40 days coincided with the time of year when Sirius, the Dog Star, rose just before the sun. The expression is still used, but owing to the precession of the equinoxes the hottest period of the year no longer coincides with this conjunction of the rising of the Dog Star and the sun.