Feather Evolution in Pennaraptora

Abstract

Two decades of paleontological discoveries of basal birds and non-avian theropods with preserved integumentary structures, especially in Late Jurassic to Early Cretaceous deposits from northeastern China, have greatly improved our understanding of the origin and early evolution of birds and their plumage. Here, we present a concise review of the plumage evolution within pennaraptora, the most inclusive clade containing Oviraptorosauria and Paraves. Feather or feather-like morphotypes were particularly diversified in non-avialan paravians, suggesting that they probably already fulfilled a wide array of biological roles, including thermoregulation and visual display. The feather-like structures in non-eumaniraptoran paravians were obviously not adapted for flight. However, Microraptor and maybe some of its relatives preserve large pennaceous feathers along the limbs and tail, similar in morphology and organization to those in modern birds, so that they could have functioned in active flight or passive gliding. Several aerodynamic innovations and flight-related morphological adaptations were (likely independently) experimented within the paravian clade close to the origin of birds. The origin and early evolution of complex feathers and flight abilities in paravian theropods were not linear processes, but more complex than previously thought.