The Dodo is a lesson in extinction. Found by Dutch soldiers around 1600 on an island in the Indian Ocean, the Dodo became extinct less than 80 years later because of deforestation, hunting, and destruction of their nests by animals brought to the island by the Dutch.
The Dodo may not always have been flightless. Dodos are related to pigeons, one group of which dispersed over water to Mauritius. There, presumably because of the lack of predators, the Dodo grew larger and became flightless.