Exceptional Preservation of Feather Micro-Structures in Amber from the Middle-Cretaceous of Myanmar

Abstract

Feathers are under-represented in the fossil record because soft tissues do not usually preserve well in sedimentary sequences. Fossil feathers are nevertheless extremely important in resolving pattern and process related to the origin of dinosaur flight. In recent years, a number of feathers have been discovered which have been mummified in amber; these feathers are preserved in three dimensions with remarkable sub-microscopic details and are especially important for our understanding of the early development of feathers. In this paper, we describe a diverse assemblage of mid-Cretaceous feathers contained within seven pieces of amber that have been recovered from northern Myanmar (Burma). These pieces include pennaceous primary feathers, contour feathers, and rachis-dominated feathers, and also a plumulaceous (downy) feather. Subcomponents of these feathers, such as barbs, barbules, and nodes are immediately recognizable. One extraordinary piece contains the distal remains of the first four primary flight feathers and a small number of possible hooklets. These pieces are discussed in terms of evolutionary development and comments are made on flight ability where appropriate. These feather-types are classified and compared with similar structures seen in Mesozoic and extant birds. We consider that integumentary feathers and ‘feather-like’ structures fall within two major structural categories (‘shafted’ and ‘non-shafted’).