Fig. 2.

Four-winged birds, today and yesterday. (A) The Peking Bantam chick epidermis expresses its feather program on the dorsal IV digit and tarsometatarsus of the foot. Téléoptile feathers, which had appeared concomitantly with the wing remiges 7 days after hatching, display at 3 weeks a remex-type and not a simple covert-type. After Prin & Dhouailly 2004. Reproduced with permission of Int J Dev Biol. (B) The well-preserved remex-type feathers at the distal hindlimb position (on tarsometatarsus) of the four-winged dinosaur Microraptor gui, the most interesting discovery among the feathered dinosaurs. After Xu et al. 2003. Reproduced with permission of the Company of Biologists. Bars: A: 5 mm, B: 5 cm.