In 2016, Lida Xing of China University of Geosciences first examined a piece of amber — or fossil tree resin — that came from a mine in northern Myanmar. He took one look at the fossil, and he knew that he had to send it to his colleague, Jingmai O’Connor of the Chinese Academy of Sciences in Beijing.

“When I was first given the specimen by Lida Xing, he’s like ‘Don’t tell anyone about this,’” Dr. O’Connor said.

The piece of amber — about 99 million years old — is smaller than a fingertip, Dr. O’Connor and a team of researchers report on Wednesday in the journal Nature, and suspended inside of it is the skull of the smallest known bird, and, therefore, dinosaur, ever discovered. They called the bird Oculudentavis khaungraae — a name that comes from the Latin words for eye, teeth and bird. The dinosaur’s skull is only 14.25 millimeters, or a little more than half an inch, from its beak to the end of its skull. The animal had bulbous eyes that looked out from the sides of its head, rather than straight ahead like the eyes of an owl or a human.

“We were able to show that this skull is even smaller than that of a bee hummingbird, which is the smallest dinosaur of all time — also the smallest bird,” Dr. O’Connor said. “This is a tiny skull, and it’s just preserved absolutely pristinely.”