Mystery Reptile Unveiled: World’s ‘Smallest Dinosaur’ Identity Revealed

Paleontologists analyzed two skulls and made the call, but aren’t sure about the exact type of animal they’ve discovered

An artist’s rendering of Oculudentavis naga

The amber-encased fossil was touted as the smallest fossil dinosaur ever found. Known from little more than a peculiar skull, and described early in 2020, Oculudentavis khaungraae was presented as a hummingbird-sized toothed bird—an avian dinosaur that fluttered around prehistoric Myanmar about 100 million years ago. But from the time this Cretaceous creature appeared in the pages of Nature, debate and controversy have circled this strange fossil and its identity. And today, in a peer-reviewed paper published in Current Biology, scientists have confirmed this small creature was no bird at all.

The original Oculudentavis fossil is preserved in a chunk of amber from the southeast Asian country of Myanmar. When it was presented in Nature in March of 2020, outside researchers quickly pointed out that Oculudentavis was not really a bird. The fossil seemed to represent a small reptile that simply resembled a bird thanks to a large eye opening in the skull and a narrow, almost beak-like snout. The original Nature paper was retracted and a reanalysis of the paper’s dataset by another team supported the idea that the fossil wasn’t a bird. A second specimen soon turned up and appeared in a pre-print the same year, adding evidence that these fossils were far from the avian perch on the tree of life. That study has since evolved into the Current Biology paper on what Oculudentavis might be, and it suggests that this bird was really a lizard.

How could a little reptile be mistaken for a bird in the first place? There are several factors that played into the confusion, says lead author and University of Bristol paleontologist Arnau Bolet. “The long and tapering snout and the vaulted skull roof gave the first fossil the overall appearance of a bird-like creature,” Bolet says. But a closer examination of the fossil, Bolet notes, showed many lizard-like traits not present in birds. The teeth of Oculudentavis are fused to the jaw, for example, which is a trait seen in lizards and snakes. And the shape and connections between particular skull bones in the fossil are seen in lizard-like reptiles and not birds. The discovery of a second possible Oculudentavis fossil helped confirm the conclusion.

Organisms preserved in amber are difficult to study from the outside, but the team created CT scans of the reptile inside the second specimen and also reanalyzed the scans from the original specimen. The second fossil differs in some ways from the first, and so Bolet and colleagues gave the second, slightly-smushed fossil a new name—Oculudentavis naga, named after the Naga people who live in the vicinity of Myanmar’s amber mines. There are enough differences between the skull bones of the two fossils that there seem to have been at least two Oculudentavis species, the researchers propose, both representing some mysterious form of lizard. Then again, outside experts like Michael Caldwell of the University of Alberta suggest, Oculudentavis might not be a lizard at all but something much more ancient and unusual.