What kind of Dog is this?

got my dog, Camber, when he was 12 weeks old from the shelter, now he is about 6 months. The shelter said that he could be shepherd, but they dont know what else. They said maybe some kind of hound or mastiff, Cur or great dane. He is already really big, about 55 pounds, and has HUGE feet. and for some reason, he is like...naturally skinny. He eats SO much, but never looks like he puts on any weight, i think it might be one of the breeds he is mixed with or something, he doesnt have worms, we already checked that. He has webbed feet,and he has a REALLY long tail, and black spots on the back of his tongue and the roof is black. Also, when the dogs next door bark at him, my spaniel will start barking back, and then Camber starts to "bay", like a hound, but he also "herds" my sisters dogs, four yorkies, he doesnt bite them or anything, but keeps them in a little herd and barks if they walk away, and then runs them back into the group. He had a Brindle brother at the shelter with him.