Update 8-3-2020, 3:45 pm EST: On July 22, 2020, the journal Nature retracted the study that this article describes. Based on the recent discovery of a similar fossil, a different team of researchers has argued that the animal was not in fact a dinosaur, but a lizard. The authors of the original study now accept that classification, but argue that their study's description of their own specimen, which was not contested in the Nature retraction, remains accurate. Our story appears in its original form below.
Some 100 million years ago in a seaside mangrove swamp in what we humans now call Myanmar, a truly bizarre dinosaur flitted about, stalking its insect prey. Its head was just a half-inch long, making it smaller than the smallest living bird, the bee hummingbird. Its mouth was packed with needle teeth, which hung over its lower beak, giving it a bit of a derpy vibe. For a bird-like predatory dinosaur, its eyes were oddly positioned on the sides of its head, meaning it probably didn’t have binocular vision.
The tiny flying dino snagged a bug here, and snagged a bug there. Then it perished somehow. And luckily for paleontologists, it got covered in sap that hardened into amber, preserving its skull in incredible detail. But despite it being a speck among its lumbering dinosaur peers, it has persisted on through the ages. Now that it has been unearthed by a team of paleontologists, it’s giving them tantalizing clues to how it lived the most miniature of lives.
It’s also raising a lot of questions, because, in technical terms, it’s also just … weird. “It just has morphologies that are all over the place, and also has morphologies that are unlike any bird or dinosaur at all,” says paleontologist Jingmai O’Connor of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who coauthored a new paper describing the specimen in the journal Nature. “Because it's so weird and because we only have a skull, it's really difficult to understand. It's this really weird evolutionary puzzle.”
Let’s try to put some pieces together. To begin with, O’Connor and her colleagues had to make sure the specimen wasn’t so small simply because it was a baby. “Only irresponsible paleontologists name species from juveniles,” O’Connor says. “The morphology is going to change.” If you think about human babies, for example, we start out with disproportionately large heads and eyes. We end up growing into them. But an important clue about this new dinosaur was that the bones of its skull were fused together when it died. (As with humans, some species are born with skulls that are not fully joined in infancy, allowing the brain to grow. The skull later fuses around it.) So here was proof that the new dino was an exceedingly tiny adult, not a baby.
Another piece of the puzzle was that tooth-packed beak. Modern birds lack teeth, of course, because of an evolutionary quirk of their lineage. In the time of the dinosaurs, the Cretaceous period, there were many bird lineages with all kinds of different teeth. But the one that gave rise to modern birds didn’t have them, so chickens and ostriches lack them as well—even species like falcons that eat meat. Fish-eating birds, though, tend to have hook-like projections in their mouths that help them hold on to their wiggling prey. “You can just Google search ‘penguin mouth,’ and it's really gross and weird,” says O’Connor.
This bird-like flying dinosaur, though, had dozens of teeth that positively packed its skull. Those teeth were actually fused to the jaw bone, which is further evidence that it was a hunter, and ran all the way back to its eye. “Which is why we gave it its name Oculudentavis, which means ‘eye tooth bird,’” says O’Connor. “I wanted to name it, like, ‘Teeny Weeny,’ but that got shot down.”
Specifically, it was a daytime hunter, as evidenced by its eye aperture, which was quite small, right for gathering abundant light during the day. (Compare this to the eye of a modern owl, which has a large aperture for gathering scant moonlight in the evening.)
The researchers also tried to figure out what kind of environment the animal stalked. Their main clue came not from the skull, but rather from the amber that encased it. Burrowing bivalves had embedded themselves inside the material—in fact, the things drilled right into the specimen’s skull. These creatures prefer brackish water like you’d find in a mangrove swamp. In addition, the amber contained the shells of squid-like critters called ammonites, which also lived in the sea.
Because the researchers only have a single skull to go on, they can’t say how Oculudentavis might have flown. Since it’s about the size of a bee hummingbird, it may have beat its wings the same way, but they can’t be sure.
But why evolve to be so small in the first place? Indeed, this dino was likely as small as its biology allows. Smaller animals lose heat more easily—a polar bear is massive in part to hold on to body heat. So being too small is bad for your survival.
The researchers think it may have shrunk way down to fill a particular role in an ecosystem. “The reason you become small, it's not because you're looking for challenges,” says O’Connor. “It's because you're trying to escape them.” If you’re as small as Oculudentavis, and can provide so little meat, maybe predators won’t even bother spending the energy hunting you. And by shrinking down to this size, Oculudentavis could exploit a niche by hunting tiny insects that its famously bulky peers wouldn’t touch. Think of it like job security. “This bird represents an ecological niche that we've never seen before,” says O’Connor. “This bird lived in a way that no other birds live today, or any bird that we know of in the fossil record.”
It’s a discovery that other researchers say further broadens science’s understanding of the diversity of the dinosaurs. The long-necked sauropods were some of the biggest vertebrates to ever walk the planet, and this new specimen must surely count as one of the smallest vertebrates ever to take flight. “It changes your perspective on what you might think of in terms of a dinosaur-dominated landscape,” says Peter Roopnarine, curator of invertebrate zoology and geology at the California Academy of Sciences, who wasn’t involved in this work. “They're occupying many niches.”
But the tiny dino’s time could not last forever. After that asteroid slammed into Earth 65 million years ago, the mammals rose to power. Dinosaurs now live on as birds, albeit birds without faces full of needle teeth. Perhaps, though, that’s for the best.