Scientists have found what they claim is the smallest known dinosaur. They described their find in the science journal “Nature.”
Paleontologists had found the tiny fossil encased in amber in northern Myanmar. They determined that it was 99 million years old, so it had lived during the Late Cretaceous Period. The fossil consisted of a bird-like skull about the size of that of a bee hummingbird (Mellisuga helenae), which is the smallest living bird and weighs a minuscule two grams. By contrast, microraptors, which were also small bird-like dinosaurs, weighed several hundred grams.
The new species has been christened Oculudentavis khaungraae, and scientists are hoping that studying the fossil can help them learn how small birds evolved from much larger dinosaurian ancestors. Professor Jingmai O’Connor from Beijing’s Chinese Academy of Sciences noted that extremely small animals face challenges such as maintaining body heat and fitting all of their sensory organs into a tiny head.
The researchers found that the new dinosaur had a novel eye structure. A bird’s eye has a bony ring called the scleral ring that gives it support. The bones making up the ring are typically square. O. khaungraae, by contrast, has spoon-shaped bones in its scleral rings – a trait seen only in some lizards.
The scientists believe that O.khaungraae had superb vision, for the bones in its scleral rings formed a cone, like the scleral rings of an owl. While an owl’s eyes face forward, however, O.khaungraae’s eyes faced sideways. Its scleral rings also had a narrow opening in their center, which would have limited the amount of light that would penetrate its eyes. That trait suggests that O.khaungraae was diurnal.
The dinosaur’s eyes also bulged outward in a way not seen in any existing animal. The scientists are thus not quite sure how its eyes worked.
The researchers also noted that O.khaungraae’s jaws had a surprising number of sharp teeth. Despite its diminutive size, it was thus probably a predator that ate insects. The scientists also found some soft tissue in the skull, including the remains of the animal’s tongue. The researchers are not sure if the dinosaur’s novel traits are due solely to its size or to extreme specialization.
Since the researchers have only a skull to work with, they are uncertain how O.khaungraae is related to other birds. Some of the features of its skull resemble those of very advanced birds, while others are more dinosaur-like.
