For 99-million-years, the skull of a tiny bird-like dinosaur has remained preserved in a blob of Burmese amber resin. Now, advanced imaging and morphological analysis suggest that the hummingbird-sized animal may represent a new species – and the smallest known bird fossil to date.
Measuring just 7.1 millimeters (0.71 centimeters) in length, the new-to-science Oculudentavis khaungraae – “eye tooth bird” – is named for its unique features. Its skull is dominated by a large eye socket that is similar to a lizard’s eye yet contains scleral ossicles, rings of bones that form in the skeletons of modern birds. A narrow opening that allows a small amount of light into the eye suggests that the animal was active during the daylight. O. khaungraae also has jaws lined with around 60 sharp, small teeth and a fossilized tongue – though teeth were common in early bird specimens, this number is oddly high. Its mouth can tell scientists a lot about the ancient animal’s lifestyle; though it is small in stature, it was likely a stealthy predator that fed on small arthropods or invertebrates rather than nectar consumed by modern hummingbirds.
The “exceptionally well-preserved and diminutive” bird-like skull provides insight into the evolution of miniaturization over tens of millions of years, suggesting that miniature body sizes in birds potentially evolved earlier than previously thought.
“This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size,” write the authors in Nature.
The size and morphology of this species suggest a previously unknown Bauplan, a set of morphological features used to describe species. But where exactly O. khaungraae fits in the evolutionary tree still remains a mystery. It may belong to enantiornithines, the most common group of birds from the Cretaceous or could be closely related to dinosaurs.
Either way, its discovery in northern Myanmar highlights the potential for new discoveries and species previously unknown to science, particularly those found in amber. Amber is formed from the resin flow from trees. Because it hardens quickly after encasing plants and animals, it is a powerful preservative that allows fragile soft tissue and skeletal anatomy to withstand environmental pressures for millions of years.
“In the past few years, Burmese amber has yielded surprising insights,” writes Roger Benson in a news release, adding that the finding presents “the potential for continued discovery remains large – especially for animals of diminutive sizes.”
Last month, researchers described the remains of a teeny tiny lizard hand similarly preserved in amber.