A recent paper by Wang et al. (2015) brings us the earliest bird of modern aspect, one from the modern Ornithomorpha clade (all living birds), Archaeornitura (Fig. 1). It lived 130 mya in the Early Cretaceous. Two specimens were found. Both had rich feather preservation with primary wing feathers long enough for flight.
Primitive, yet modern
The sternum is small. The ventral pelvis is gracile. The sacrum is large and robust, but not fused together and not fused to the ilium. At least one specimen appears to have retained a long set of tail bones. The coracoids were long and firmly attached to a large sternum, though not nearly as large as in modern flying birds. The fingers were reduced, but unfused. The skull was not well preserved in either specimen. About nine not-very-long cervicals were present. Not much, if any, of a pubic boot in Archaeornithura, but all sister tested sister taxa have one.
Compare the skeleton
of Archaeornithura (Fig. 1) to that of Gallus the chicken (Fig. 2). The chicken, like most modern birds, has a larger, deeper sternum, a larger deeper ventral pelvis, fused fingers and more cervicals.
So, in pterosaurs and their predecessors
the pectoral and pelvic girdles came first, the wings developed later. In birds, the wings came first, the pectoral and pelvic girdles took a while to develop.
Wang M et al. (7 other authors) 2015. The oldest record of ornithuromorpha from the early cretaceous of China. 6:6987 DOI: 10.1038/ncomms7987