Prevalent among the Amer-Indian peoples, particularly the Algonquin and Cheyene, are legends telling of immense birds, and raging storms that would come in their wake. Interestingly, reported sightings of birds of truly monstrous proportions persist, most frequently through the vicinity of the Sierra Madre mountain range in Mexico. In the Miocene era, approximately eight to ten million years ago, a species of bird, discovered in only 1979 and dubbed "Argentaevis Magnificens," (which means 'Magnificent Bird of Argentina') soared through South American skies, with a wing-span of 25 feet and weighing perhaps 200 lbs! Just maybe...

The mythological Thunderbird is a mythical creature common to Indigenous spirituality. According to the book "Mythological Monsters", its wing span is 3 miles long, and it has a head that grows from its chest. It is a popular concept in northwestern coastal artwork of indigenous origin, often appearing on totem poles.

Thunderbird is a term used in cryptozoology to describe large, bird-like creatures, generally identified with the Thunderbird of Native American myth and folklore. Similar cryptids reported in the Old World are often called rocs. Although Rocs are generally regarded as being eagles like the gigantic Haast eagle of New Zealand, that if no direct fossil evidence had been discovered would surely have been relegated to the world of mythology, thunderbirds on the otherhand are regarded by a small number of researchers as having lizard features like the pterosaurs and pteranodon and hence not mythological.