How did oviraptors bring their babies into the world? These feathered, bird-like dinosaurs couldn’t fly, but scientists have long wondered whether they incubated their eggs like modern birds or were more dependent on environmental heat like crocodiles and turtles.
A new study was published in Frontiers in Ecology and Evolution Considers the question afresh. Researchers in Taiwan combined physical experiments with computer simulations to investigate how Oviraptor eggs warmed up and how efficiently they hatched. To do this, they built a life-size model of an Oviraptor and recreated its nest using artificial eggs.
The results suggest that the position of the brooding adult relative to the eggs played an important role in the development of the eggs.
“We show that differences in Oviraptor hatching patterns were driven by the relative position of the adult incubating the eggs,” said senior author Dr. Tzu-Rui Yang, associate curator of vertebrate paleontology at the National Museum of Natural Sciences in Taiwan.
The study also found that Oviraptor incubation was less efficient than that of modern birds.
“In addition, we obtained an estimate of the incubation efficiency of oviraptors, which is much lower than that of modern birds,” said first author Chun-Yu Su, who attended Washington High School in Taichung during the research.
Oviraptors
Oviraptor was a group of feathered, bird-like dinosaurs that lived during the Late Cretaceous period, approximately 100 to 66 million years ago. Despite their name, which means “egg thief”, scientists now believe they were not stealing eggs. The first Oviraptor fossil was discovered near a nest, leading researchers to mistakenly assume it was raiding it. Later discoveries revealed that the dinosaur was probably caring for its eggs on its own.
These relatively small to medium-sized dinosaurs had beak-like jaws, long necks, and often had crests on their heads. Most species were probably omnivorous, eating a variety of foods that may have included plants, seeds, eggs, shellfish, and small animals. Fossils found in Asia, particularly Mongolia and China, have provided remarkable evidence of nesting behaviour, including adults preserved in crouching positions over their nests.
Oviraptors are particularly important to scientists because they help highlight the evolutionary transition from non-avian dinosaurs to modern birds. Their plumage, nesting habits, and parental care behavior suggest that many traits associated with birds evolved long before the first true birds appeared.
Reconstruction of an ancient dinosaur nest
The researchers based their reconstruction on heyuaniya huaengiAn Oviraptor species that lived in what is now China between 70 and 66 million years ago. The dinosaur was about 1.5 meters tall, weighed about 20 kilograms, and built semi-open nests that contained several rings of eggs.
To recreate the animal, the team constructed the torso using a wooden structure and polystyrene foam. Cotton, cloth, and bubble paper were added to represent soft tissues. The eggs were molded from resin and arranged in double rings that matched the layout seen in fossilized Oviraptor nests.
Creating a realistic model was not easy.
“Part of the difficulty lies in realistically reconstructing oviraptor incubation,” Su said. “For example, their eggs are different from the eggs of any living species, so we invented resin eggs to approximate real Oviraptor eggs as closely as possible.”
Sunlight may have played a major role
The team tested how different environmental conditions and the presence of an anxious adult affected the temperature of the eggs.
In cold conditions, a difference of up to 6°C was observed in the temperature of eggs in the outer ring of the nest as observed by an adult. Such variation can cause asynchronous hatching, meaning that some eggs are hatched earlier than others within the same clutch.
In warmer conditions, the temperature difference between eggs in the outer ring dropped to only 0.6°C. This discovery suggests that oviraptors living in warmer environments may have experienced different hatching patterns because sunlight provides an additional source of heat.
“It is unlikely that large dinosaurs sat on top of their clutches. Supposedly, they used the heat of the sun or the soil to incubate their eggs, like turtles. Since Oviraptor clutches are open to the air, the heat of the sun matters more than the heat of the soil,” Yang explained.
How did oviraptors compare to modern birds
The researchers also examined how Oviraptor incubation stood out compared to modern birds.
Most birds use thermoregulatory contact incubation (TCI), in which adults transfer body heat directly to the eggs by sitting on them. This strategy depends on three conditions. The parents should touch each egg, serve as the primary heat source, and keep all eggs within a relatively narrow temperature range.
Oviraptors couldn’t possibly meet those requirements. Their distinctive nest design prevented the adults from making direct contact with each egg at once.
“Oviraptors may not have been able to conduct TCI like modern birds,” Su said. Instead, these dinosaurs and the sun may have been co-incubators – less efficient than the incubation behavior displayed by modern birds. Nevertheless, the combination of adult incubation and ambient heat source – perhaps a behavioral adaptation linked to the evolution from buried to semi-open nests – is not necessarily worse.
According to Yang, this comparison should not be seen as a competition between dinosaurs and birds.
Yang explained, “Modern birds are not ‘better’ at incubating eggs. Instead, birds and oviraptors living today have a very different method of incubation or, more specifically, brooding.” “Nothing is better or worse. It just depends on the environment.”
New insights into dinosaur domestication
The researchers emphasize that their findings relate to the reconstructed nests used in the study. They also noted that Earth’s climate today is significantly different from conditions during the Late Cretaceous, which could influence the results. It is also thought that oviraptors had a longer incubation period than modern birds.
Nevertheless, this work provides an innovative approach to studying dinosaur reproduction. By combining physical reconstructions with heat transfer modeling, researchers were able to explore questions that have traditionally been difficult to investigate using fossils alone.
Yang concluded, “This is really an encouragement for all students, especially in Taiwan.” “There are no dinosaur fossils in Taiwan but that doesn’t mean we can’t study dinosaurs.”