Feather-like development of Triassic diapsid skin appendages
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Of the recent sauropsid skin appendage types, only feathers develop from a cylindrical epidermal invagination, the follicle, and show hierarchical branching. Fossilized integuments of Mesozoic diapsids have been interpreted as follicular and potential feather homologues, an idea particularly controversially discussed for the elongate dorsal skin projections of the small diapsid Longisquama insignis from the Triassic of Kyrgyzstan. Based on new finds and their comparison with the type material, we show that Longisquama’s appendages consist of a single-branched internal frame enclosed by a flexible outer membrane. Not supporting a categorization either as feathers or as scales, our analysis demonstrates that the Longisquama appendages formed in a two-stage, feather-like developmental process, representing an unusual early example for the evolutionary plasticity of sauropsid integument.
KeywordsFossilized integument Skin appendage Feather evo-devo Longisquama
This work was supported by the German Research Foundation (DFG II - VO 1466/1–1) and by the Society of Vertebrate Paleontology (Patterson Memorial Grant to JF). We are thankful to Evgenii N. Kurochkin and Vladimir R. Alifanov for access to the type material in Moscow in February 2007, to Susan Turner and Jörg W. Schneider for suggestions and comments, and to Ilja Kogan for his help with the translation of Russian publications and reports.
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