Sequential moult in a feathered dinosaur and implications

Kiat Y., Balaban, A., Sapir, N., O'Connor, J., Wang, M. and Xu, X. 2020. Sequential moult in a feathered dinosaur and implications for early paravian ecology and locomotion. Current Biology 30:3633-3638.

Feather molt is an important life-history process in birds, but little is known about its evolutionary history. Here, we report on the first fossilized evidence of sequential wing feather molt, a common strategy among extant birds, identified in the Early Cretaceous four-winged dromaeosaurid Microraptor. Analysis of wing feather molt patterns and ecological properties in extant birds imply that Microraptor maintained its flight ability throughout the entire annual cycle, including the molt period. Therefore, we conclude that flight was essential for either its daily foraging or escaping from predators. Our findings propose that the development of sequential molt is the outcome of evolutionary forces to maintain flight capability throughout the entire annual cycle in both extant birds and non-avialan paravian dinosaurs from 120 mya

Examples of Two Molt Strategies: (1) Sequential Molt and (2) Non-sequential Molt

(A) Marbled godwit Limosa fedoa during a sequential molt that includes gradual and directional replacement of the wing’s flight feathers, starting from the innermost primary and moving outward toward the wing’s distal tip (credit: G. Gartner). (B) Flightless cormorant Nannopterum harrisi during a non-sequential molt that includes an irregular, gradual replacement of its flight feathers; both wings present a mixture of old, new, and growing feathers without any order or symmetry between the two wings (credit: T. Salmond). (C) Common loon Gavia immer after simultaneous shedding of all the wing’s flight feathers as part of its non-sequential simultaneous molt (credit: S.P. d’Entremont). (D) African darter Anhinga rufa that is characterized by a non-sequential molt, in which its flight feathers grow simultaneously (credit: L. Francey).