Thunderbird is a term used in cryptozoology

Cryptozoology

Cryptozoology refers to the search for animals whose existence has not been proven...

 to describe large, bird-like creatures, generally identified with the Thunderbird

Thunderbird (mythology)

The Thunderbird is a legendary creature in certain North American indigenous peoples' history and culture. It is considered a "supernatural" bird of power and strength...

 of Native American

Native Americans in the United States

Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

 tradition. Similar cryptid

Cryptid

In cryptozoology and sometimes in cryptobotany, a cryptid is a creature or plant whose existence has been suggested but is unrecognized by scientific consensus and often regarded as highly unlikely. Famous examples include the Yeti in the Himalayas and the Loch Ness Monster in...

s reported in the Old World

Old World

The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....

 are often called Rocs. Thunderbirds are regarded by a small number of researchers as having lizard features like the extinct pterosaurs such as Pteranodon

Pteranodon

Pteranodon , from the Late Cretaceous geological period of North America in present day Kansas, Alabama, Nebraska, Wyoming, and South Dakota, was one of the largest pterosaur genera and had a maximum wingspan of over...

. Reports of Thunderbird sightings go back centuries, and the fossil record does show that giant birds (teratorns) with wingspans between 12 and 18 ft (3.7 and 5.5 m) were likely contemporary with early man.