The specimen is an oviraptorosaur, a bird-like theropod dinosaur that thrived during the Cretaceous Period, commonly known as the “Age of Dinosaurs.”
The dinosaur was recovered in Ganzhou City in southern China’s Jiangxi Province, preserved in Cretaceous-aged rocks that date back as far as 70 million years.
“Dinosaurs preserved on their nests are rare, and so are fossil embryos,” said study co-author Dr. Shundong Bi. “This is the first time a non-avian dinosaur has been found, sitting on a nest of eggs that preserve embryos, in a single spectacular specimen.”
The fossil contains the incomplete skeleton of a large oviraptorid crouched in a bird-like brooding posture over a clutch of two dozen eggs. At least seven of these eggs preserve bones or partial skeletons of unhatched embryos inside.
The close proximity of the adult to the eggs, as well as the late stage of development of the embryos, indicates that the dinosaur died in the act of incubating its nest.
Prior to this study, a few other oviraptorid skeletons have been found sitting on nests. The analyses of those fossils concluded that the animals were simply laying eggs or guarding the nests.
However, the new study suggests that oviraptorosaurs incubated their eggs to keep them at the proper temperature like modern birds.
“This kind of discovery, in essence fossilized behavior, is the rarest of the rare in dinosaurs,” explained Dr. Matthew C. Lamanna. “Though a few adult oviraptorids have been found on nests of their eggs before, no embryos have ever been found inside those eggs.”
“In the new specimen, the babies were almost ready to hatch, which tells us beyond a doubt that this oviraptorid had tended its nest for quite a long time. This dinosaur was a caring parent that ultimately gave its life while nurturing its young.”
The researchers conducted oxygen isotope analyses on the eggs, which revealed that they had been incubated at high temperatures. This supports the theory that the adult dinosaur died in the act of brooding its nest.
While all of the embryos were well-developed, some were more mature than others, suggesting that oviraptorid eggs of the same clutch may have hatched at slightly different times. Asynchronous hatching appears to have evolved independently in oviraptorosaurs and some modern birds.
“It’s extraordinary to think how much biological information is captured in just this single fossil,” said Dr. Xing Xu. “We’re going to be learning from this specimen for many years to come.”
The study is published in the journal Science Bulletin.