Well, what interesting dragon art to run across. I definitely like it; it's well done. Ever seen, let alone drawn an adamantine dragon? They don't look too different from this one, actually; definitely bigger, more horns, more robust wings (more robust overall really) and the fin runs all the way down its back but otherwise? Quite similar, coloration aside. Weellll that's assuming one goes by their original description from 2nd edition D&D. The 4th edition version is A.) nerfed into the ground and B.) looks like a bad science project.
I honestly never referenced my dragons to the D&D versions really. First of all because I like giving myself enough space to imagine the dragon. I did had a few commissions asking specifically for D&D dragon species exactly (did a few black and blue dragons like that) but if I have a choice, I always try to imagine my own dragons.
Believe it or not, this dragon I did way before even the 3th edition of D&D. Description was rather simple and it allowed me to just go the way I imagined it. I mostly do my dragons European style but I had done dragons asian style and also made a few non flying races as well, not to mention subraces of dragons, like wyverns and alike.
At first glance it can appear as a three legged dragon, but if you consider the pose and look closer there is definitely enough form to show that there is a fourth limb. You just have to look at the shadows and highlights properly.