不会飞行的鸟类的进化历程

Because of their far-flung（遥远的，广泛的） geography and colorful examples including the African ostrich¹（鸵鸟）, Australian emu, New Zealand kiwi and long lost giants such as the New Zealand moa, Baker², et. al. have examined a fascinating part in the story of the avian tree of life: flightless birds, or ratites（平胸类鸟）. Straddling the middle ground is the South American tinamous which can fly, and thus were not grouped within the flightless ratites but rather considered as close relatives according to the shared structure of their palate bones. In contrast, recent molecular³ studies have suggested they may be more closely related to the extinct moa（恐鸟） within the ratites.   To help pin down the evolutionary⁴ debate, Baker's research team utilized⁵ ancient moa DNA⁶ (from the extinct little bush moa) along with DNA from emus and other flightless birds to assemble the largest dataset to date (1448 genetic⁷ loci and 8 corroborating⁸ rare genomic events).   Their results, published in the advanced online edition of Molecular Biology and Evolution, found convincing evidence that tinamous are indeed most closely related to the wingless extinct moa, and thus flight has been lost independently in ratite lineages. They showed that morphological characters of ratites interpreted on their molecular tree are mostly convergent⁹, evolving independently, probably as an adaptation to a cursorial（善于奔跑的）, "on-the-run" lifestyle.