Faux Cynthia, Field Daniel J
Department of Integrated Physiology and Neurosciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99164, USA
Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA.
Biol Lett. 2017 Jul;13(7). doi: 10.1098/rsbl.2017.0234.
Recent phylogenetic studies question the monophyly of ratites (large, flightless birds incorporating ostriches, rheas, kiwis, emus and cassowaries), suggesting their paraphyly with respect to flying tinamous (Tinamidae). Flightlessness and large body size have thus likely evolved repeatedly among ratites, and separately in ostriches () and emus (). Here, we test this hypothesis with data from wing developmental trajectories in ostriches, emus, tinamous and chickens. We find the rate of ostrich embryonic wing growth falls within the range of variation exhibited by flying taxa (tinamous and chickens), but that of emus is extremely slow. These results indicate flightlessness was acquired by different developmental mechanisms in the ancestors of ostriches (peramorphosis) and the emu-cassowary clade (paedomorphosis), and corroborate the hypothesis that flight loss has evolved repeatedly among ratites.
最近的系统发育研究对平胸鸟类（包括鸵鸟、美洲鸵、几维鸟、鸸鹋和食火鸡的大型不会飞的鸟类）的单系性提出了质疑，表明它们相对于会飞的䳍形目鸟类（䳍科）是并系的。因此，不会飞和大体型可能在平胸鸟类中反复进化，并且在鸵鸟和鸸鹋中是独立进化的。在这里，我们用鸵鸟、鸸鹋、䳍形目鸟类和鸡的翅膀发育轨迹数据来检验这一假设。我们发现鸵鸟胚胎翅膀生长速率落在会飞类群（䳍形目鸟类和鸡）所表现出的变异范围内，但鸸鹋的生长速率极其缓慢。这些结果表明，鸵鸟的祖先（形态过度发生）和鸸鹋 - 食火鸡分支（幼态持续）通过不同的发育机制获得了不会飞的特性，并证实了平胸鸟类中飞行能力丧失是反复进化的这一假设。
