How long have dogs been alive?

Canned food first appeared in the early 1900's, complete compound dry feeds appeared in the 50's and 60's. Dog meal (to be mixed with meat) was certainly available in the 1880's. Before diet aimed specifically at dogs, there was always the knacker - the person who took fallen and condemned stock for rendering. Going back into the mists of time there were trenchers - slabs of rough bread used before plates were generally available - they were destined to be dog food at the end of the meal.