Japanese crossword «Shepherd»

Canis lupus and Canis lupus familiaris can be hard to tell apart! I heard of a baggage handler at an airport who thought a grey wolf on its way to a zoo was a German Shepherd, so he took it for a walk on a leash, with no trouble. Anyway, I don't understand the definition of species anymore. I was taught that different species could not produce fertile offspring together, but there seems to be a whole complex of Canis species (different kinds of wolves, coyotes, jackals, dingos, dogs) which can and sometimes do interbreed and produce fertile offspring.