Multiple dragon species

I belief there are multiple species of dragons in the world of avatar as we see the dragons of Roku and Sozin:

Who's heads are more different then those from Ran and Shaw:

And then you have Druk, Zuko's dragon who looks a bit more like a European dragon (just a bit):

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I think they're different species. I've seen this pointed out before and imo you're definitely right.

Like different breeds of dogs, per se? I can see that, actually.

What do you think?