Abstract：
Feather moulting is a crucial process in the avian life cycle, which evolved to maintain plumage functionality. However, moulting involves both energetic and functional costs. During moulting, plumage function temporarily decreases between the shedding of old feathers and the full growth of new ones. In flying taxa, a gradual and sequential replacement of flight feathers evolved to maintain aerodynamic capabilities during the moulting period. Little is known about the moult strategies of non-avian pennaraptoran dinosaurs and stem birds, before the emergence of crown lineage. Here, we report on two Early Cretaceous pygostylian birds from the Yixian Formation (125 mya), probably referable to Confuciusornithiformes, exhibiting morphological characteristics that suggest a gradual and sequential moult of wing flight feathers. Short primary feathers interpreted as immature are symmetrically present on both wings, as is typical among extant flying birds. Our survey of the enormous collection of the Tianyu Museum confirms previous findings that evidence of active moult in non-neornithine pennaraptorans is rare and likely indicates a moult cycle greater than one year. Documenting moult in Mesozoic feathered dinosaurs is critical for understanding their ecology, locomotor ability and the evolution of this important life-history process in birds.
摘要：
羽毛蜕皮是禽类生命周期中至关重要的过程,进化来保持羽毛的功能。然而,换羽涉及能量和功能成本。在蜕皮期间，在旧羽毛脱落和新羽毛充分生长之间，羽毛功能暂时下降。在飞行分类单元，逐渐和顺序更换飞行羽毛，以保持换羽期间的空气动力学能力。关于非鸟类pennaraptoran恐龙和茎鸟的蜕皮策略知之甚少，在冠谱系出现之前。这里,我们报道了来自义县组（125mya）的两只早白垩世pyogstylian鸟，可能是指儒家鸟甲，表现出的形态特征表明机翼飞行羽毛的逐渐和顺序蜕变。被解释为未成熟的短初级羽毛对称地存在于两个翅膀上，这是典型的现存的飞鸟。我们对天宇博物馆的大量藏品的调查证实了先前的发现，即非新鸟氨酸pennaraptorans中活跃蜕皮的证据很少见，并且可能表明蜕皮周期大于一年。记录中生代羽毛恐龙的蜕皮对于了解其生态学至关重要，鸟类的运动能力和这一重要生活史过程的演变。
