The dinosaur Oviraptor, or egg thief, was previously thought to have been a dinosaur egg consumer, as its fossilized remains were often found near nests. But when scientists uncovered an 80-million-year-old fossil, it showed this bipedal, carnivorous dinosaur (approximately the size of a modern ostrich) was apparently brooding or guarding a nest of 15 large eggs.

The fossil, uncovered in Mongolia’s Gobi Desert in the mid–1990s, is the first hard evidence to date showing the behavior of this dinosaur. Other theories on the dinosaur’s behavior have been inferred from indirect data. An Oviraptor was found lying on its clutch of eggs, with its legs tucked tightly against its body, and the arms turned back to encircle the nest. This is similar to the nesting behavior of modern birds, and it suggests such behaviors may have started long before the advent of wings and feathers.