Nowadays we might conflate many mythical creatures under the heading of dragon but to the heraldic artists there was a whole menagerie of quite distinct beasts, the wyvern being one of them. A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Cockatrice Whilst both the dragon and wyvern are winged and scaled, the wyvern stands on two legs rather than four. Wade suggests, somewhat plausibly that both creatures may have arisen through garbled descriptions of the crocodile. The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P26