The story insinuates that dogs may have been in more than just companion roles in some of these cases.
Remains of a dog were found tangled with those of a Roman-era sailor when those ancient ships (and port) were discovered a few years ago at Pisa, Italy. I saw it suggested at that time that, rather than the sailor jumping in to save his dog, it was probably the other way around.
"Man is a dog's ideal of what God should be." -- Mark Twain