What is a dog?

Besides man's best friend, of course? I was reading on Wikipedia the other day. I did know that the domestic dog is very closely related to the gray wolf. I did not know the dog as we know it today is thought to be the first animal to be domesticated.

Remains of domesticated dogs, about 33,000 years old, have been found in Siberia. Dogs and humans have been companions for 33,000 years! What a mind-boggling number!

I also did not know these first dogs seem to be of a lineage extinct today. Today's dogs have existed for about 15,000 years.