I've been practicing over the last two weeks . I based a couple of the designs above on a crocodiles head...when I do that though I think of the crocodile singing in 'all dogs go to heaven'. I don't know why.
When I saw this I instantly wanted to write a critique for it, but now that I'm here I don't know what to say! These are really great studies using various angles. I can't say I've seen any other studies like this but the design of the head isn't too uncommon. Each head has a good balance to it and comes off as dragon like. I think I like the two on the left hand side the best, especially the head on view one but they all work well and would each make a nice drawing. Over all I think you should be very happy with these.