A co-publish from the University of Saskatchewan and the China University of Geosciences describes an entire wing preserved in amber from 99 million years ago. (They have the two wings actually.) The wing is of a type of bird called an Enantiornithe (“opposite bird”) which is a family of birds who were once older cousins to, and later the main rivals of the type of bird we have today (Neornithes.)
This beautiful wing is much more like that of modern birds than we might have suspected — although there are claws (Hoatzins are the only modern birds that retain claws, and only in the young), the types of feathers and their arrangement are exactly the same as modern birds. It was suspected that Enantiornithes might have needed a different feather arrangement, as some of these birds didn’t have a fan of feathers on their tails (some did, but others evolved long tails.)
What is fascinating about this is that the wing is fully formed and flight ready — and yet, as tiny as it is, must be a chick’s. It has long been suspected that Enantiornithes might have been ready for flight shortly after pecking their way out of the egg, and this adds to that suspicion, as this bird was not in the nest, but clambering on a tree (just as the aforementioned Hoatzin is able to do.) That’s the coolest thing about these birds, potentially — flying chicks!
Sadly, we don’t have the rest of the bird. Amber is often used for jewelry, and the study notes that this piece has been polished, and possibly chipped away the rest of the bird. That would have been truly fascinating — we think Enantiornithes retained a more dinosaur-like maw, they had teeth, and we might have had a peek at the face of a dinosaur if the rest of the bird were there.