Judging from what appears to be a partial crest I assume he's a mutt.
That very erect tail reminds me of pictures of Japanese bantams. As for a partial crest, I had a lovely fellow that had the same feature--he also had an extra rear toe on each foot--both the extra toes and crests are typical for silkies, along with feathers down the legs, which he also had.
I agree that your lovely lad is likely that most beloved of creatures--the great american mutt. Hope he gives you as much pleasure as my 'Hot Stuff' gave me!