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The Plumage of Basal Birds

  • Jingmai O’ConnorEmail author
Chapter
Part of the Fascinating Life Sciences book series (FLS)

Abstract

Early bird plumage is well known primarily due to numerous discoveries of specimens preserving feathers from Early Cretaceous deposits in China. Remiges and rectrices are most commonly preserved with rectrices showing the greatest variation. The long boney-tailed Jeholornis has a unique tail plumage employing two anatomically distinct rectricial pterylae serving both aerodynamic and ornamental functions. Basal pygostylians show disparate tail plumages that are reflected by differences in pygostyle morphology. Sapeornis has a proportionately shorter pygostyle wielding a fan-shaped array of rectrices, whereas the robust pygostyle of Confuciusornis is associated with a pair of elongate rachis-dominated feathers in some specimens, considered indicative of sexual dimorphism. The latter morphology is also present in many enantiornithines. Members of this diverse clade have primarily ornamental tail morphologies, whereas the earliest members of the Ornithuromorpha all possess tail morphologies that appear to be primarily aerodynamic. Body feathers in Archaeopteryx and adult enantiornithines trapped in amber are pennaceous suggesting that reported rachis-less body feathers in Jehol birds may be taphonomic artifacts. Rarely preserved, well-developed pennaceous crural feathers are present in Archaeopteryx and some enantiornithines, whereas crural feathers are short in the Confuciusornithiformes. Their preserved absence in nearly all Jehol ornithuromorph specimens most-likely reflects the smaller available sample size. Crural feathers in many basal ornithuromorphs were probably reduced, as in Yanornis and extant aquatic and semiaquatic birds. Overall, early birds show a trend towards the reduction of the distal hindlimb feathers present in closely related nonavian dinosaurs. However, well-developed tarsometatarsal feathers are present in Sapeornis and two exceptionally well-preserved enantiornithine specimens indicate this group was diverse in the distal extent of their hindlimb plumage, including at least one lineage with feathered pedal digits. Although remarkably modern in many aspects, early bird plumage still differed from that of their modern counterparts including extinct morphotypes and differences in ontogenetic patterns.

Keywords

Aves Plumage Jehol avifauna Enantiornithes Basal birds Rachis-dominated tail feathers 

Notes

Acknowledgements

I would like to thank X-T. Zheng of the STM, H-L. Chang of the Henan Geological Museum, and C-L. Gao of the DNHM for access to specimens. I would also like to thank C. Sullivan and T. Stidham of the IVPP for useful discussions and M. Rothman for use of his art work.

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© Springer Nature Switzerland AG 2020

Authors and Affiliations

  1. 1.Key Laboratory of Vertebrate Evolution and Human OriginsInstitute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of SciencesBeijingChina
  2. 2.CAS Center for Excellence in Life and PaleoenvironmentBeijingChina

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