Wyvern folklore is rarely fire-breathing like the four-legged dragon. Sometimes modern fantasy book and media authors have wyverns that are frost-breathing or poison-breathing instead of fire-breathing. The current spelling "wyvern" is not attested before the seventeenth century as "winged two-footed dragon". According to the Oxford English Dictionary, it is an alteration of Middle English "wyver" (attested thirteenth century), from Anglo-French "wivre" (cf. French "guivre" and "vouivre"), which originate from Latin "vīpera", meaning "viper", "adder", or "asp". Conversely, medievalist William Sayers proposes a more complex origin for the term. He notes that the Anglo-French "guivre" and its Middle English derivative ceased to
Mexican heraldry of these rules is a key to the art of heraldry. This system was adapted to Mexican society by incorporating flora and fauna native to Mexico. Another conspicuous difference between Mexican heraldry and European heraldry is the absence of a helm surmounting the shield. Most traditions of Mexican heraldry came from Hispanic or Spanish origin from regions in Spain or Portugal, predominating heraldry of Castilian, Basque or Galician, in second place heraldry of Catalan and Valencian origin. Other common heraldic traditions in Mexico came from French, Italian, German and Polish origins. The most recent heraldic influences, since 1943, are of