Most dragons are portrayed as reptilian, complete with scales, long body, and short legs. The closest modern creature to a dragon would be a lizard, even though the lizard is tiny compared to the dragon. Iguanas seem especially dragonlike, but without the long graceful neck. Dinosaurs must have been real dragons, even without the wings and the fiery breath. I did this study of lizard legs, front and back, copied from identification photographs in the Audubon Guide to Reptiles and Amphibians. It's interesting that the lizard front legs can be almost humanoid, with five-digit "hands," but the grasping talons are not at all like our fingers and the lizards have no opposable thumb. The lizards also have a lower stance than a mammal would. There are some dragons without wings, and many of the Old World or alchemical portrayals of dragons were based on fanciful renderings of crocodiles.
Other dragons have a mammalian form, like this one which I copied, with some adaptation, from Jessica Peffer's dragon drawing book. Unlike the reptile dragon, this quadruped is goat or horse-like, though with feet, balancing tail, and horns from other animals. This mammalian dragon has a hide, tufts of hair, and a mane rather than scales and spikes. The wings are adapted from bat wing shapes, another mammal's feature. The mammalian dragon, which was also portrayed in ancient times, looks less fierce than a reptilian dragon.
Lizard legs are pencil on 8 1/2" x 11" sketchbook page. Mammalian dragon is pencil on sketchbook page, 7" x 6". February 29-March 1, 2012. Click on drawing for a larger view.