Believe it t or not, the clucking little barnyard chicken has a fearsome ancestry: It descends from dinosaurs. One group of dinosaurs called the theropods, which included the legendary Tyrannosaurus rex, evolved to walk on two legs, freeing up their arms to use for grasping and, millions of years later, for flying. And these dinosaurs had another special adaptation: They evolved thin, tubular feathers, which likely helped keep them warm.
The path from theropod to chicken saw dinosaurs evolving into birds. Then emerged a branch that was made up of stocky, mostly ground-dwelling birds called Galliformes, which today includes modern pheasants, turkeys, grouse, and others. Then humans got involved, guiding the evolution of a wild pheasant into our domestic chicken, the most numerous bird on Earth.