Can dogs get depressed over the loss of another dog?

I visit your web site frequently. It has great info, I can often find answers to my questions just by reading your articles or answers that you have given others. Now, however, I have a question that I've never seen addressed anywhere. This may sound a little strange, but here goes... Can dogs get depressed? We have a 19 month old German Shepherd Dog, called Tango, who comes from German and Czech lines. He's a great dog, obedient and a pleasure to work with. Lately though he seems sad. We had to have my 5 year old cocker spaniel put down about a month ago due to health and genetic problems. She had been his "friend" and playmate since we brought him home at 7 weeks. In the evenings he seems especially sad. This was the time of day when both dogs would "hang out" with my husband and I. Tango will come up and lay his head in one of our laps and softly whine or moan. It's not the kind of whine that says he wants something. He just seems sad. He will also lie on the floor with his head on his paws and just look at us and sigh and sometimes softly moan or whine. Again he doesn't seem to want anything. He started this behavior a few days after her passing. If he were a person I would certainly think he's sad and/or depressed. Have you ever heard of anything like this? Do you think he could be missing Jessie (my cocker) and sad (like me) because she's no longer here? If so, is there anything you know of that we can do to help him?

Thanks for your time.
Susan