Flight is typically regarded as an evolutionary marvel and a defining characteristic of birds, however, there have been dozens of species that have thrived by evolving a more terrestrial lifestyle. Flightlessness has typically evolved in environments where flight, and the various tradeoffs necessary to both achieve and sustain this, are a total net-negative in terms of fitness or survivability. Some of these consequences of flight include the the high cost during development, the morphological trade offs necessary to have a body that can efficiently flight and the increased metabolic needs to sustain flight. Environments where flight would not be beneficial are places with low rates of predation or low competition for resources. It could also evolve due to the lack of necessity, as there are terrestrial niches that would favor larger size and beaks (predatory role). Dodo bird, Giant Moa and Phorusrhacos all lost flight (lack of predation, increased E to size, predatory role) specifically. These species seem to exhibit Neoteny or retention of juvenile characteristics as opposed to complete recession of wing development as they still have a not well ossified sternum and obtuse scapula-coracoid joint. Also, developmental heterochrony, which shortens the embryonic process of wing development
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