Encased in a translucent sheath of amber for almost 100 million years and narrowly escaping a fate as jewelry, two tiny dinosaur-era bird wing fossils are finally getting the recognition they deserve. Lida Xing, a lecturer at the China University of Geosciences, and Professor Ryan McKellar from the University of Regina and the Royal Saskatchewan Museum, published their analysis of the fossils in the journal Nature Communications last week. Although less than 2 cm long, they are some of the best preserved dinosaur-era bird wing specimens, complete with bone, skin, muscle, claws, and feathers.
Right place, right time
While at an amber market, most of us would simply be admiring the stones. Lida Xing, on the other hand, looks for signs of animal and plant life. Burmese amber contains a phenomenal variety of life from the Cretaceous period, but its mining and sale is mostly unregulated. These particular pieces had been sold to a Chinese jewelry maker who intended to fashion a necklace from them called “Angel’s Wings”. But Xing and his international research team found the samples first.
“We were extremely lucky… the wings were tiny, and it took a lot of skill to recognize their scientific importance,” says Prof. McKellar.
“Everybody knew that insects could be preserved in amber, but unexpected kinds fossils have recently been discovered in this medium,” says Dr. François Therrien, Curator of Dinosaur Palaeoecology and the Royal Tyrrell Museum of Palaeontology in Alberta. “From now on, I’ll be collecting every piece of amber I find in the field, that’s for sure!”
A young man going into the amber mine, Danai area, Burma. Photo credit: Mo Li
Skin and bone (and feather)
Fossils preserved in amber generally retain more detail and three-dimensional structure than their counterparts in rock, but for wings, have only yielded single feathers completely dissociated from any remaining tissue or bone structure. This makes species identification impossible.
That’s why these fossils are so unique. They each consist of wing tips complete with bone, skin, muscle, claws, and feathers with microscopic preservation down to the level of individual feather barbules and their pigment distributions.
Compound microscope image of barbule pigmentation banding in one of the fossils. Photo credit: Royal Saskatchewan Museum (RSM/ R.C. McKellar)
“The presence of feathers in Cretaceous amber [is] amazing enough, to get a whole wing is off the charts,” says Dr. Don Brinkman, Director of Preservation and Research also at the Royal Tyrrell Museum.
“The preservation of these tiny wings is stunning. It looks like they were trapped in resin yesterday,” says Darla Zelenitsky, Assistant Professor of Dinosaur Paleobiology at the University of Calgary.
The proportions of the bones in the wings suggests that they are both from members of the group Enantiornithes, the most diverse and abundant types of birds during the Cretaceous. The small size of the fossils suggests young, hummingbird-sized juveniles.
Somewhat gruesomely, one of the fossils had claw marks within the resin, suggesting that the small bird had been buried in amber while still alive, the rest of the skeleton likely chipped away and discarded as an impure stone within the Burmese mines.
Birds of a feather
The fact that modern birds are descended from dinosaurs is largely accepted, but the unprecedented level of detail in these fossils show just how similar they were. The positioning of the feathers on the surface of the wing and the microscopic structure are remarkably similar to today’s birds.
The plumage was also quite adult-like despite the small size of the fossils, suggesting that these birds were capable of flying shortly after hatching. It is also the first time colour patterns could be identified for this group of birds.
One of the fossils and life-size reconstruction of Enantiornis by Shenna Wang.
“They were well-camouflaged, with walnut coloured upper wing surfaces marked by a spot and band pattern created by paler feathers, and the underside of the wings covered by nearly white plumage,” says Prof. McKellar.
The researchers intend to continue studies of the fossils with non-destructive techniques, but already, it’s becoming much easier to paint a picture of these creatures in our minds.
“It puts us in touch with the Cretaceous in a way that is unparalleled and it really shows that the fossil record still has unexpected surprises for us,” says Brinkman.