The most intact bird fossil in 99-million-year-old amber.

The newly discovered bird is also special because researchers were able to get a clearer view of the internal structure of the young prehistoric creature, according to study co-author Ryan McKellar of the Royal Saskatchewan Museum in Regina, Canada.

"The amber is opaque and contains many small wood splinters. It appears to have formed on or near the forest floor," McKellar observed. This means the bird's external appearance isn't particularly remarkable, but its internal structure is far more interesting. "When preparing for the study in Myanmar, they polished the front half of the specimen, allowing us to observe the chest cavity and skull," McKellar said.

The discovery adds to the already remarkable collection of Cretaceous fossils from the amber mine north of the Hukawng Valley in Myanmar. Over the past few years, the area has yielded several striking bird wing fossils, the intact tail of a small carnivorous dinosaur, and the skeleton of a newly hatched bird. Last December, researchers even found the remains of dinosaur blood-sucking ticks embedded in the amber.

Lida Xing, the lead author of the study detailing the specimen in the journal Science Bulletin, shared that when she first saw the bird being sold as jewelry in Myanmar in 2015, her heart raced. The research team was fortunate enough to acquire the bird for the Dexu Institute of Paleontology in Chaozhou, China. Amber-encased birds can sometimes fetch prices as high as $500,000, beyond the reach of scientists, according to Xing, a paleontologist at the University of Geosciences in Beijing.

Based on the analysis, the research team concluded that the young bird became entangled in the tree sap while still alive or already dead. The moisture caused the sap to bubble slightly, subsequently forming an opaque amber mass. Some bones and soft tissue were lost, and sediment became trapped within the voids.

The bird was about 6 cm long. Its feather and bone structure suggested it was an enantiornithine, a primitive bird that went extinct along with flightless dinosaurs 66 million years ago. "Even though they were newly hatched, they already had full feathers on their wings and tails. They had weak spines, so they probably weren't great flyers," McKellar speculated.

When alive, the bird had teeth in its beak and a chestnut or walnut-colored body, with fluffy feathers on its head and neck. Unfortunately, the fossil lacks two identifying features: a toothed beak and claws on its wings. Researchers believe the young bird may have been attacked by predators and fallen from its nest onto sap oozing from the same tree. Some plant fragments and cockroaches found in the amber may have originated from the nest.