99-Million-Year-Old Amber Preserves Skull of Hummingbird-Sized Dinosaur
Paleontologists have found an exceptionally well-preserved and diminutive skull of a previously unknown bird-like dinosaur species in a piece of Cretaceous-period amber from northern Myanmar.
The newly-identified species, named Oculudentavis khaungraae, could represent the smallest known Mesozoic dinosaur in the fossil record.
Its size is on par with that of the bee hummingbird (Mellisuga helenae), the smallest living bird.
“Amber preservation of vertebrates is rare, and this provides us a window into the world of dinosaurs at the lowest end of the body-size spectrum,” said Dr. Lars Schmitz, a researcher in the W. M. Keck Science Department at Claremont McKenna, Scripps and Pitzer Colleges.
“Its unique anatomical features point to one of the smallest and most ancient birds ever found.”
The piece of amber, just 31 x 20 x 8.5 mm, containing the skull of Oculudentavis khaungraae came from the Angbamo site near Tanai in the Hukawng valley of Myanmar’s Kachin province.
Dr. Schmitz and colleagues studied the specimen’s distinct features with high-resolution synchrotron scans to determine how the skull differs from those of other bird-like dinosaur specimens.
They found that the shape and size of the eye bones suggested a diurnal lifestyle, but also revealed surprising similarities to the eyes of modern lizards.
The skull also shows a unique pattern of fusion between different bone elements, as well as the presence of teeth.
“The specimen’s tiny size and unusual form suggests a never-before-seen combination of features,” the scientists said.
“The discovery represents a specimen previously missing from the fossil record and provides new implications for understanding the evolution of birds, demonstrating the extreme miniaturization of avian body sizes early in the evolutionary process.”
The specimen’s preservation also highlights amber deposits’ potential to reveal the lowest limits of vertebrate body size.
“No other group of living birds features species with similarly small crania in adults,” Dr. Schmitz said.
“This discovery shows us that we have only a small glimpse of what tiny vertebrates looked like in the age of the dinosaurs.”
The findings are published in the journal Nature.
L. Xing et al. 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature 579, 245-249; doi: 10.1038/s41586-020-2068-4