Fig. 1
From: Bone-associated gene evolution and the origin of flight in birds
Skeleton adaptations in birds and mammals and adaptive selection in bone-associated genes. a Rock pigeon skeleton (adapted from Wikimedia Commons licensed under a Creative Commons Attribution-Share Alike 3.0 Unported (CC BY-SA 3.0)) showing the key bone modifications observed in birds, and bones containing red-blood-cell-producing marrow (apneumatic bones). Most bones (except very small ones) are pneumatized. The structure of a pneumatic bone is highlighted in the light blue box (licensed by Rice University under a Creative Commons Attribution License (CC-BY 3.0)). b Positively selected genes in birds and those genes showing a dissimilar evolutionary rate in bats when compared to other mammals (lower evolutionary rate—colored in grey; and higher evolutionary rate—colored in white). Representation of the link between gene and physiological/development systems (colored accordingly: skeleton system (1), muscular system (2) and glucose (3) that are plausibly related with flight adaptation