Ancient baby bird preserved beautifully in amber

The Hukawng Valley mines of Myanmar (Burma) are famous treasure troves of amber. These chunks of fossilised tree sap have long been sought after for their beauty, but scientists are more interested in the remains of ancient creatures they often hold inside. Over the past several months, Burmese amber discoveries have included alien-looking insects, a feathery dinosaur tail and now the latest – and perhaps greatest – surprise: a nearly complete baby bird!

Much of the bird is hidden deep within the 78-gram piece of amber, with only its claws clearly visible from the outside. In fact, it was originally acquired in 2014 by the Hupoge Amber Museum in China from a miner who thought the claws belonged to a lizard. But when the museum director sent the fossil along to the birds-in-amber experts, they were able to CT-scan the fossil and reveal the incredible secrets within.

Inside this hardened resin is the most complete bird ever found in Burmese amber. A 100-million-year-old baby bird! Image: Lida Xing

"When we saw the original photos, it looked like there were just a couple of feet in the amber piece, but once we had the CT data on hand, it became obvious that we were dealing with a lot more," said Ryan McKellar of the Royal Saskatchewan Museum.

The preserved bird body includes the head, neck, part of the right wing, both legs and the hints of a tail, all covered with skin, scales and lots of feathers. From the CT scan, the researchers were able to digitally reconstruct many of these features without having to damage the specimen itself. From snout to tail, this ancient hatchling is about six centimetres (2.5 in) long.

CT-scanning the fossil allowed researchers to digitally reconstruct the bones (bottom), and an artist to draw a reconstruction of what the hatchling may have looked like (right). Art by Chung-Tat Cheung; Image: Jingmai O'Connor

This is not a bird like we know them today – it belonged to an extinct group called the enantiornithes, ancient cousins of modern birds. These extinct birds were winged and covered in feathers, but still retained certain features of their reptilian ancestors which modern birds have lost, such as teeth. This baby lived 100 million years ago, in the world of the Late Cretaceous Period, where early birds and large non-bird dinosaurs lived side by side.

The state of development of the bird's bones and feathers indicates that it had just hatched. "It's captured mid-way through its first moult," McKellar explained, "so we can look at the tail and actually see sheathed feathers that haven't unfurled." The researchers estimate this bird died only weeks, perhaps even just a matter of days, after hatching.

Even though it was fresh from the egg, the hatchling was ready to face the world. Unlike most modern birds, which are born fairly helpless, this newborn already had a full set of flight feathers on its wings, suggesting that enantiornithine birds were ready to fly shortly after hatching. This adds to growing evidence that these animals weren't big on parental care after birth.

"In a lot of modern birds that have this sort of lifestyle, the hatching occurs on the ground and then it's sort of a scramble to get into the trees to get away from predators," McKellar said. "It appears we're seeing the same thing with these enantiornithines."

He added that this lifestyle might even explain why this bird ultimately ended up in the hands of palaeontologists. "I'm guessing that part of the reason we're seeing so many of these juveniles or hatchling specimens trapped in Burmese amber is that there's a lot of mortality on the way up the trees or in the first few weeks of life."

This fossil has been nicknamed "Belone" by the palaeontologists, a local term for the amber-coloured Oriental skylark.

Among the other features visible on "Belone" are the patterns of colours on its feathers, the fine scales on its feet, an eyelid and an ear opening! It also possessed some unusual bristle-like feathers that are quite different from what we see in modern-day birds, but similar to the "protofeathers" known from many non-bird dinosaurs.

From the outside, the bird’s feet are clearly visible, complete with claws, scales, and even preserved skin! Image: Ming Bai

In recent years, McKellar and colleagues have had the good fortune to access a lot of the fantastic fossils coming out of the Burmese amber mines. As miners continue to work, not only are other museums, like the Hupoge Amber Museum, keeping an eye out for interesting specimens, but McKellar has noted that their research has inspired some private collectors to share their specimens for study as well.

McKellar admitted he couldn't say too much about what else is known from these amber deposits – we'll have to wait for the official scientific publications for more juicy details – but he hinted that there is a lot more where this bird came from. "It's sort of the tip of the iceberg in terms of the material coming out of this site."