Burmese amber contains skull of hummingbird-sized dinosaur.

Science News reports on the discovery of the smallest known dinosaur in a Myanmar gemstone – and it was a tiny predator:

A tiny, toothed bird that lived 99 million years ago appears to be the smallest known Mesozoic dinosaur, an era from about 252 million to 66 million years ago. The creature’s 12-millimeter-long skull was found encased in a chunk of amber originally discovered in northern Myanmar, researchers report March 11 in Nature.

Of modern birds — the only dinosaurs still living today — the bee hummingbird is the smallest. The new species, dubbed Oculudentavis khaungraae, was similar in size.

“It had more teeth than any other Mesozoic bird, regardless of size,” says paleontologist Jingmai O’Connor at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. As for its prey, researchers can only guess, she adds. O. khaungraae probably dined on arthropods and invertebrates, and possibly even small fish.

The ancient bird also had deep, conical eye sockets, similar to those of modern predatory birds such as owls. Those deep sockets can increase the eye’s visual ability without increasing its diameter, and suggest the ancient birds had sharp eyesight, O’Connor says. But while owls’ eyes face forward, increasing their depth perception, the eyes of the tiny bird faced out to the side.

The miniaturization may be related to island dwarfism, in which larger animals evolve to smaller body sizes over many generations because their ranges are strictly limited, such as on an island. Anecdotal evidence suggests that the chunk of amber containing the bird skull may have come from a region in Myanmar that millions of years ago was part of an island chain.