World’s first preserved dinosaur sitting on egg nest with fossilized babies

The fossil in question is that of an oviraptorosaur, a group of theropod bird-like dinosaurs that flourished during the Cretaceous Period, the third and final period of the Mesozoic Era (commonly referred to as the ‘Age of Dinosaurs’ ‘) which stretched from 145 to 66 million years ago. The new specimen was recovered from the tallest Cretaceous rocks, around 70 million years old, in the city of Ganzhou, in southern China’s Jiangxi province.

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

The fossil consists of an incomplete skeleton of a large, presumably adult oviraptorid crouching in a brooding posture similar to that of a bird on a clutch of at least 24 eggs. At least seven of these eggs keep partial bones or skeletons of unhatched oviraptorid embryos inside. The late stage of embryo development and the proximity of the adult to the eggs strongly suggest that the latter died while incubating its nest, like its modern bird cousins, rather than laying its eggs or simply guarding its nest. crocodile- style, as has sometimes been proposed for the few other oviraptorid skeletons found atop nests.

“This type of discovery, essentially fossilized behavior, is the rarest of the few in dinosaurs,” says Dr. Lamanna. “Although a few adult oviraptorids have already been found on egg nests, no embryos have ever been found inside these eggs. In the new specimen, the babies were almost ready to hatch, which tells us no doubt this oviraptorid tended its nest for quite a long time. This dinosaur was a caring parent who ultimately gave his life while feeding his young. “

The team also performed oxygen isotope analyzes which indicate that the eggs were incubated at high temperatures, similar to those of birds, further supporting the hypothesis that the adult perished while incubating his nest. Additionally, while all of the embryos are well developed, some appear to have been more mature than others, which in turn suggests that oviraptorid eggs in the same clutch may have hatched at slightly different times. This feature, known as asynchronous hatching, appears to have evolved independently in oviraptorids and some modern birds.

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

Said Dr. Xu, “It’s amazing to think of the amount of biological information captured in this single fossil. We will learn from this specimen for many years to come.”