A new specimen belonging to a group of bird-like theropod dinosaurs was found sitting on a nest of eggs complete with fossilized young in Ganzhou City, Jiangxi Province, Southern China.
The fossil belongs to an oviraptorosaur - dinosaurs with three-toed limbs and avian features, such as feathers - found embedded among the uppermost Cretaceous Period rocks estimated to be about 70 million years old. Their species flourished during the Cretaceous (145.5 to 65.5 million years ago), following the Jurassic as the third and last of the Mesozoic Era, also known as the Age of the Dinosaurs.
"Dinosaurs preserved on their nests are rare, and so are fossil embryos," noted Dr. Shundong Bi, one of the authors of the study, in a news release from Science China Press. He remarks that this discovery marks the first that a non-avian dinosaur has been found on a nest of eggs with preserved embryos, all in a single specimen.
Details of the Ganzhou City discovery are published in a report titled "An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaurs," appearing in the recent Science Bulletin.
Impressive Find of Dinosaur Parent and Child
The fossil found in China is made up of an incomplete oviraptorid - large and presumed to be an adult - preserved in a crouching position over a nest containing at least 24 eggs. Researchers have already found preserved bones or partial skeletons of still unhatched oviraptorid youngs in at least seven of the eggs. Based on the condition of the embryos - in the late stages of fetal development - and the close proximity of the adult to these eggs have led the researchers to infer that the adult oviraptorid died while it was incubating its brood. This behavior is similar to its modern avian relatives - instead of just laying its eggs - or guarding its nest like crocodiles do, which has been previously suggested for other oviraptorid fossils found near or on top of nests.
"This kind of discovery, in essence fossilized behavior, is the rarest of the rare in dinosaurs," Dr. Matthew Lamanna, a co-author of the study from the Carnegie Museum of Natural History. He adds that while a few oviraptorids have been previously discovered, this find is the first to have embryos preserved inside the eggs. Furthermore, some of the babies in the nest were "almost ready to hatch," which indicates that the adult oviraptorid had tended to the nest for quite some time.
"This dinosaur was a caring parent that ultimately gave its life while nurturing its young," Lamanna added.
Further Evidence of Parental Care in the Dinosaur
Researchers also conducted oxygen isotope analyses on the discovered specimen, finding that the eggs were incubated at high temperatures comparable to modern birds' incubating environments. Furthermore, since the embryos within the fossilized eggs are well-developed - although some of them are in more developed stages than the others - suggests that oviraptorid eggs in the same batch might have hatched at different times. This behavior, known as asynchronous hatching, is widely believed to have evolved separately in some modern birds.
Furthermore, researchers were able to discover a cluster of pebbles in its abdominal regions. These are most probably gastroliths - birds ingest rocks on purpose to help them break down hard food materials. This discovery is also the first instance that these gastroliths have been found in oviraptorids.
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