The world’s first preserved dinosaur sitting in an egg nest with fossilized babies

The fossil in question is that of an oviraptorosaurus, a group of bird-like theropod dinosaurs that prospered during the Cretaceous period, the third and final period of the Mesozoic Era (commonly known as the ‘Age of Dinosaurs’) that extended from 145 to 66 million years ago. The new specimen was recovered from rocks from the upper Cretaceous period, some 70 million years old, in the city of Ganzhou, in southern China’s Jiangxi province.

“Dinosaurs preserved in their nests are rare, as are fossil embryos. This is the first time that a non-avian dinosaur has been found, sitting in a nest of eggs that preserve embryos, in a single spectacular specimen,” explains Dr. Shundong Bi.

The fossil consists of an incomplete skeleton of a large oviraptorid, presumably adult, crouched in a bird litter laying on a litter of at least 24 eggs. At least seven of these eggs preserve bones or partial skeletons of oviraptorid embryos not hatched inside. The late stage of development of the embryos and the adult’s proximity to the eggs strongly suggests that the latter died in the act of incubating its nest, like its modern bird cousins, instead of laying its eggs or simply guarding its crocodile-style nest, as it was sometimes proposed for the few other oviraptorid skeletons that were found on top of the nests.

“This type of discovery, essentially fossilized behavior, is the rarest of the rare dinosaurs,” explains Dr. Lamanna. “Although some adult oviraptorids have been found in their egg nests before, no embryos have been found inside those eggs. In the new sample, the babies were almost ready to hatch, which tells us, without a doubt, that this oviraptoride had treated his nest for a long time. This dinosaur was a caring father who ultimately gave his life while feeding his young. “

The team also conducted oxygen isotope analyzes that indicate that eggs were incubated at high bird temperatures, adding more support to the hypothesis that the adult died in the act of hatching its nest. In addition, although all embryos were well developed, some appear to be more mature than others, which in turn suggests that oviraptorid eggs in the same litter may have hatched at slightly different times. This characteristic, known as asynchronous incubation, seems to have evolved independently in oviraptorids and in some modern birds.

Another interesting aspect of the new oviraptorid specimen is that the adult preserves a cluster of pebbles in its abdominal region. They are almost certainly gastrolytes, or “stomach stones”, rocks that would have been deliberately swallowed to help the dinosaur digest its food. This is the first time that undoubted gastrolytes have been found in an oviraptoride and, as such, these stones may provide new insights into the diet of these animals.

Dr. Xu says: “It is extraordinary to think how much biological information is captured only in this single fossil. We will learn from this specimen for many years.”