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. Author manuscript; available in PMC: 2020 Nov 27.
Published in final edited form as: Cell. 2019 Nov 27;179(6):1409–1423.e17. doi: 10.1016/j.cell.2019.11.008

Figure 6. Diverse Rachis and Barbule Architectures Represent Adaptations of Fundamental Morphological Prototypes.

Figure 6.

(A and A′) Feather shaft cross sections from birds living in different ecospaces show unique architectural adaptations (A). Feather collection areas, red arrow. Highlight of feather rachis architectural adaptations in different eco-environments (A′). Ostrich body feather rachis dorsal cortex shows a secondary medullary zone (A2, two left panels). White arrows, unclear cortex/medulla identity with vacuoles in the cortex (A2, right panel). Scale bars, blue: 100 μm; black: 500 μm.

(B) Schematic summary of prototypic feather branching architectures depicting rachis with cortex and medulla and barbs with three different barbule shapes: filamentous (plumulaceous), plate, and hooklet (pennaceous).

(C) Detail structure of distal and proximal barbules in adult chicken flight (top row) and ostrich flight feathers (bottom row). Note the loss of hooklets in ostrich flight feathers.

(D) Mesozoic feathers preserved in amber. Top row: pennaceous-like barbs. Bottom row: plumulaceous-like barbs. Pennaceous-like barbules do not display distal and proximal hooklet structures. Green arrows, ramus proximal/distal axis. Red arrows, rachis proximal/distal axis. For (C) and (D), green, blue, and red boxes represent magnified regions of proximal and distal areas.