Fossils: Amber preserves ancient bird wings

Two 99 million-year-old bird wings fossilized in Burmese amber are described in a study published in Nature Communications this week. The fossils - which include the first examples of hair follicles and feather arrangements from the Cretaceous (about 145.5 to 65.5 million years ago) - provide a rare glimpse into the development of juvenile wings in ancient birds.

Previously, our knowledge of bird wings and plumage from the Cretaceous has come from two-dimensional fossils (carbonaceous compressions) and individual feathers preserved in amber. Although valuable, these fossils do not provide as much information as three-dimensional specimens such as those described in the present study.

Lida Xing, Ryan McKellar and colleagues found two fossil specimens at a site in the Kachin Province of Myanmar that was previously dated to about 99 million years old. They examined the structure and arrangement of the bones and feathers in the fossils using techniques such as synchrotron X-ray micro CT scanning. Comparison with other fossil species suggests that the wings belonged to enantiornithine birds - a lineage of birds which became extinct at the end of the Cretaceous. Based on the small size of the wings and the incomplete development of the bones, the authors believe the specimens were juveniles at the time of death, but the advanced development of their feathers suggests that the birds were relatively mature at hatching (precocial).

The authors note that, overall, the plumage of the fossil wings closely resembles that of modern birds: in fact, most of the feather types are the same and display similar arrangement, pigmentation and microstructure.