Flightless bird more species of flightless birds (including the kiwi, several species of penguins, the takahe, the weka, the moa, and several other extinct species) than any other such location. One reason is that until the arrival of humans roughly a thousand years ago, there were no large land predators in New Zealand; the main predators of flightless birds were larger birds. Ratites belong to the superorder Palaeognathae birds, which include the volant tinamou, and are believed to have evolved flightlessness independently multiple times within their own group. Some birds evolved flightlessness in response to the absence of predators, for example on
Evolution of birds more rigid ribcage with a carina and shoulders able to allow for a powerful upstroke, essential to sustained powered flight. Another improvement was the appearance of an alula, used to achieve better control of landing or flight at low speeds. They also had a more derived pygostyle, with a ploughshare-shaped end. An early example is "Yanornis". Many were coastal birds, strikingly resembling modern shorebirds, like "Ichthyornis", or ducks, like" Gansus". Some evolved as swimming hunters, like the Hesperornithiformes – a group of flightless divers resembling grebes and loons. While modern in most respects, most of these birds retained typical reptilian-like