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.”
Bee hummingbirds, which are still alive today and found in Cuba, have braincases — for birds, that means the skull minus the length of the beak — that measure about 8.8 millimeters long, while the braincase of Oculudentavis is about 7.1 millimeters, or just over a quarter of an inch long. Oculudentavis also has more teeth in its mouth than any other known fossil bird, suggesting the bird was a predator that hunted other creatures.
That it sported so many teeth, though, creates confusion about the evolutionary history of dinosaurs and birds.
Most scientists now believe that birds are theropods, dinosaurs of a group that included tyrannosaurus and spinosaurus, but that birds were on their own evolutionary branch from a common ancestor. Paleontologists have long assumed that as birds evolved away from other dinosaurs, having teeth was a trait that was in the process of disappearing altogether. “But this specimen strongly shows that evolution’s really going in all different directions,” Dr. O’Connor said.
Ed Stanley, a research scientist at the Florida Museum of Natural History who was not involved in the new study, said “the interesting thing about this is how unlike a bird this looks.”
“It doesn’t look like any bird I’ve ever seen,” he added.
When Dr. Stanley first saw the specimen, he thought that it was a pterosaur — flying reptiles closely related to, but which were not themselves, dinosaurs. Such doubt will linger, he explained, until remains are found that reveal what the rest of the body of Oculudentavis looked like — and whether those remains bear any bird features.
Dr. O’Connor said, “It’s just a skull, and there are no features preserved in it that are like ‘this is definitively avian.’”
“We have so little information right now,” he said.
Unearthing even a skull like this one, however, was an extremely lucky discovery. The odds of finding another Oculudentavis specimen, Dr. O’Connor quipped, are about “.0001 percent, or something.”