Skull of smallest-known bird embedded in 99-million-year-old amber

WASHINGTON (Reuters) – Scientists are marveling over the exquisitely preserved skull of what appears to be the smallest-known bird – tinier than any hummingbird – encased in 99-million-year-old amber and boasting many odd traits including jaws studded with numerous puny teeth.

The skull, measuring about half an inch (14.25 mm) long, belongs to a bird called Oculudentavis khaungraae that lived during the Cretaceous Period in what is now northern Myanmar, the researchers said on Wednesday. None of the rest of the body was preserved, but the researchers estimated that Oculudentavis weighed about an ounce (28 grams) and measured 2 inches (5 cm) long including a hypothetical bony tail.

“I was totally blown away,” said paleontologist Jingmai O’Connor of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, describing her reaction upon seeing the fossil. “It’s probably the most beautifully preserved Mesozoic bird skull I’ve ever seen, and it’s so weird.”

The Mesozoic Era was the age of the dinosaurs.

“I was amazed,” added Natural History Museum of Los Angeles County paleontologist and study co-author Luis Chiappe.

O’Connor said Oculudentavis appeared to be smaller than a bee hummingbird, until now considered the world’s littlest bird.

Oculudentavis shares few similarities, aside from size, with hummingbirds, which like all modern birds lack teeth and eat nectar. Many Mesozoic birds had teeth, but Oculudentavis possessed the most – about 100, with a conical shape and sharp ridges on the edges. Oculudentavis likely hunted insects. Hummingbirds have long beaks, unlike Oculudentavis.

Birds evolved from small feathered dinosaurs roughly 150 million years ago. Oculudentavis illustrates the almost-incomprehensible size difference among members of the dinosaur lineage, contrasting to contemporaneous South American long-necked, pillar-legged dinosaur Argentinosaurus at perhaps 90 tons and 115 feet (35 meters).

“The size diversity hints at the amazing biology of dinosaurs, capable of sustaining such a diversity of forms,” said O’Connor, who led the research published in the journal Nature.

Its eyes resembled those of owls, with the eye bones forming a cone, indicating acute vision, O’Connor said. Unlike birds of prey with forward-facing eyes and binocular vision enabling good depth perception, the eyes in Oculudentavis faced to the sides and bulged out of its head. The small size of the aperture of the eye bones indicates Oculudentavis was active during daytime.

Amber – fossilized tree sap – has preserved numerous small organisms including insects, lizards and frogs.

“Amber is just amazing as a preservational medium,” O’Connor said. “If the animal does not decay much before getting entombed in resin, the preservation is phenomenal: All the soft tissues preserved in three dimensions, like a window into an ancient world.”