However a newly identified fossil of the birds’ common ancestor is helping paleontologists piece together the shared past of swifts and hummingbirds. The fossil — that of Eocypselus rowei — is notable particularly for the preservation of its feathers, making reconstruction of the wings far more accurate than from skeletal remains alone.

E. rowei, found in the fossil-rich Green River Formation in southwestern Wyoming, lived 50 million years ago and was less than five inches long from head to tail.

Like hummingbirds and swifts, the small bird had a notably stout humerus, or upper-arm bone. According to a reconstruction based on its bones and feathers, however, E. rowei’s wing shape differed from both of its modern relatives. The wing represents an intermediate shape between the two, suggesting the Pan-Apodiformes lineage evolved a small body shape first before splitting into different wing shapes and flight characteristics, according to findings published today in the Proceedings of the Royal Society B.