Smallest-ever fossil dinosaur found trapped in amber
The little bird-like dinosaur Oculudentavis khaungraae probably dined on insects in a Cretaceous rainforest.
A spectacular new amber
fossil from Myanmar holds the skull of the smallest prehistoric dinosaur
ever found: a bird-like creature that lived 99 million years ago and
grew no bigger than the smallest birds alive today.
The fossil, described today in the journal Nature,
measures just 1.5 centimeters long from the back of the head to the tip
of the snout, about the width of a thumbnail. The skull's proportions
suggest that the animal was about the same size as a bee hummingbird,
which would have made the newfound dinosaur lighter than a dime.
The tiny creature appears to be most closely related to the feathered dinosaurs Archaeopteryx and Jeholornis,
distant cousins of modern birds. Researchers suspect that like those
animals, the small dinosaur had feathery wings, but without more
fossils, they can't determine how well it flew. And despite its
hummingbird-like proportions, the tiny dinosaur was no nectar feeder.
Its upper jaw bristled with 40 sharp teeth, and its huge eyes—suited for
spotting prey in the foliage—have features unlike any seen in other
dinosaurs. Fittingly, the creature’s genus name is Oculudentavis, derived from the Latin words for eye, tooth, and bird.
No creature alive today is built quite like Oculudentavis. “It’s revealing a completely different ecological niche that we never knew existed,” says study coauthor Jingmai O’Connor,
a paleontologist at China’s Institute of Vertebrate Paleontology and
Paleoanthropology. “It’s fun, but it’s also a total puzzle, and
everything about it is so weird.”
“This is truly one of the rarest and most spectacular of finds!”
University of Central Florida paleontologist Ryan Carney, who wasn’t
involved with the study, says in an email. “Like capturing Cretaceous
lightning in a bottle, this amber preserves an unprecedented snapshot of
a miniature dinosaur skull with exciting new features.”
A snout of sharp teeth
When Lida Xing
first saw the fossil, he thought it was “too strange.” The
paleontologist at the Chinese University of Geosciences and lead author
of the new study thought the animal’s long snout and large eyes
suggested it was an early bird. But Xing was surprised that it had so
many teeth, seemingly more than any other toothed bird from the
Cretaceous. A full 23 teeth, each less than half a millimeter long, stud
the creature’s upper right jaw alone.
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To get a better look at the skull, Xing took the lump of amber to a
high-powered x-ray facility in Shanghai to capture features as tiny as
the width of a red blood cell. He then sent the scans to O’Connor, a
specialist in bird-related dinosaurs, and what she saw gobsmacked her.
“This [fossil] was so pristine and so well-preserved,” O’Connor says. “This thing was super perfect.”
To suss out the dinosaur’s relative age, O’Connor and her colleagues
pored over scans of the skull and looked at how much its bones had fused
together, an indication of the animal’s maturity. The researchers
determined that Oculudentavis died at or near adulthood—making its petite size all the more unusual.
Eyes like no other bird
The unusual creature also had eyes so large, they would have bulged
out of the sides of its head. Puzzled, O’Connor decided to contact
paleontology’s “eye guy,” Lars Schmitz, a researcher at California’s W.M. Keck Science Department who studies the evolution of vision.
When Schmitz first saw the skull scans, he realized that the eyes
resembled smaller birds’ proportionately large eyes, which strengthened
the case that the Oculudentavis fossil came from an adult.
Reptiles and birds have small bony rings in their eyes that help
support the visual organs. The plates comprising these rings are usually
shaped like narrow rectangles, but in Oculudentavis, the tiny
bones are shaped like ice cream scoops. “The shape you see there, that
isn’t really seen in any other bird, or any other dinosaur,” Schmitz
says.
The only animals today with similarly scoop-shaped eye bones are diurnal lizards. As far as the researchers can tell, Oculudentavis used its unusually large eyes to forage during the day, snapping up insects with its toothed snout.
The most similar bird today might be the tody, a small-bodied Caribbean bird that preys on insects, says Jen Bright, a biologist and bird skull specialist at the University of Hull. But tody skulls are twice the size of the Oculudentavis fossil. “To find a vertebrate fossil this small is kind of mind-blowing,” she says. “It’s such a weirdo, I love it!”
A piece of amber less than 1.5 inches wide contains the entire skull of Oculudentavis khaungraae, a newfound type of dinosaur that lived in what is now Myanmar 99 million years ago.
Photograph by Xing Lida
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