Birds first truly evolved in the Cretaceous period although their reptilian ancestors can be found in the fossil record throughout the Mesozoic in such extinct dinosaur species as Micro Raptor and Archaeopteryx. Birds evolved true flight, and with it, a warm blooded metabolism enabling them to reach parts of the world that other reptiles could not otherwise. In their newly colonized habitats, birds have adapted to fill as many niches as possible creating a large diversity amongst them. This diversity is often sought after by humans, particularly birder watchers, birders or twitchers to see these beautiful animals in their natural habitats. While this does not represent the entirety of species observed, it acts to demonstrate the vast diversity of colouration, shape and size among bird species.