An Enantiornithine with a Fan-Shaped Tail, and the Evolution of the Rectricial Complex in Early Birds

• Published in: Current biology Vol. 26; no. 1; pp. 114 - 119
• Main Authors: O’Connor, Jingmai K., Wang, Xiaoli, Zheng, Xiaoting, Hu, Han, Zhang, Xiaomei, Zhou, Zhonghe
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 11.01.2016
• Subjects: Animals; Biological Evolution; Birds - anatomy & histology; Birds - physiology; Cretaceous; Enantiornithes; Feathers; Fossils; Jehol; Paleontology; Pengornis; Phylogeny; Pygostylia; rectrix; Spine - anatomy & histology; tail; Tail - anatomy & histology; Tail - physiology; rectrix; tail; Enantiornithes; Jehol; Pengornis; Pygostylia; Cretaceous
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2015.11.036

The most basal avians Archaeopteryx and Jeholornis have elongate reptilian tails. However, all other birds (Pygostylia) have an abbreviated tail that ends in a fused element called the pygostyle. In extant birds, this is typically associated with a fleshy structure called the rectricial bulb that secures the tail feathers (rectrices) [1]. The bulbi rectricium muscle controls the spread of the rectrices during flight. This ability to manipulate tail shape greatly increases flight function [2, 3]. The Jehol avifauna preserves the earliest known pygostylians and a diversity of rectrices. However, no fossil directly elucidates this important skeletal transition. Differences in plumage and pygostyle morphology between clades of Early Cretaceous birds led to the hypothesis that rectricial bulbs co-evolved with the plough-shaped pygostyle of the Ornithuromorpha [4]. A newly discovered pengornithid, Chiappeavis magnapremaxillo gen. et sp. nov., preserves strong evidence that enantiornithines possessed aerodynamic rectricial fans. The consistent co-occurrence of short pygostyle morphology with clear aerodynamic tail fans in the Ornithuromorpha, the Sapeornithiformes, and now the Pengornithidae strongly supports inferences that these features co-evolved with the rectricial bulbs as a “rectricial complex.” Most parsimoniously, rectricial bulbs are plesiomorphic to Pygostylia and were lost in confuciusornithiforms and some enantiornithines, although morphological differences suggest three independent origins. •O’Connor et al. name a new pengornithid enantiornithine honoring Dr. Luis Chiappe•The new specimen preserves strong evidence that an aerodynamic tail is present•These new data suggest that Shanweiniao had ornamental feathers•The unique pengornithid pygostyle may possess simple rectricial bulbs O’Connor et al. describe a new pengornithid enantiornithine preserving an array of tail feathers forming an aerodynamic surface. In basal birds, aerodynamic tails co-occur with proportionately shorter pygostyles, suggesting that rectricial bulbs were present in at least some enantiornithines and the basal pygostylian Sapeornis.