How oviraptors, bird-like but flightless dinosaurs, hatched their eggs has long been unclear. Did they depend on heat from their surroundings like crocodiles, or did they warm their eggs directly like birds? A new study in Frontiers in Ecology and Evolution explores this question by examining oviraptor nesting behavior and hatching patterns.
Researchers in Taiwan combined heat transfer simulations with physical experiments to better understand how these dinosaurs incubated their eggs. They also compared their findings with modern bird incubation. To do this, they built a life size model of an oviraptor and a realistic nest to test how heat moved through the eggs.
"We show the difference in oviraptor hatching patterns was induced by the relative position of the incubating adult to the eggs," said senior author Dr. Tzu-Ruei Yang, an associate curator of vertebrate paleontology at Taiwan's National Museum of Natural Science.
"Moreover, we obtained an estimate of the incubation efficiency of oviraptors, which is much lower than that of modern birds," added first author Chun-Yu Su, who attended Washington High School in Taichung when the research was conducted.
The model was based on Heyuannia huangi, an oviraptor species that lived between 70 and 66 million years ago in what is now China. This dinosaur was about 1.5 meters long and weighed around 20kg. It built semi-open nests arranged in multiple rings of eggs.
To recreate the animal, researchers constructed the torso using polystyrene foam and a wooden frame, then added cotton, bubble paper, and fabric to mimic soft tissues. The eggs were made from casting resin. In the experiments, two clutches were arranged in double rings to match fossil evidence.
"Part of the difficulty lies in reconstructing oviraptor incubation realistically," said Su. "For example, their eggs are unlike those of any living species, so we invented the resin eggs to approximate real oviraptor eggs as best as we could."
Heat, Nest Design, and Hatching Patterns
The team tested how both adult presence and environmental conditions affected egg temperatures and hatching outcomes.
In colder conditions, when a brooding adult was present, temperatures in the outer ring of eggs varied by as much as 6°C. Such differences could lead to asynchronous hatching, where eggs in the same nest hatch at different times. In warmer environments, that variation dropped to about 0.6°C. This suggests that in warmer climates, sunlight may have helped even out temperatures and influenced hatching patterns.
"It's unlikely that large dinosaurs sat atop their clutches. Supposedly, they used the heat of the sun or soil to hatch their eggs, like turtles. Since oviraptor clutches are open to the air, heat from the sun likely mattered much more than heat from the soil," Yang explained.
The researchers also compared oviraptor incubation to that of modern birds. Most birds rely on thermoregulatory contact incubation (TCI), where adults sit directly on their eggs and provide heat. For TCI to work, the adult must touch all the eggs, act as the main heat source, and keep temperatures consistent.
Oviraptors likely could not meet these conditions. Their ring shaped egg arrangement meant the adult could not maintain contact with every egg at once.
"Oviraptors may not have been able to conduct TCI as modern birds do," said Su. Instead, these dinosaurs and environmental heat likely worked together, making them co-incubators. While this method was less efficient than that of modern birds, it may have been well suited to their nesting style, which appears to have shifted from buried nests to semi-open ones.
"Modern birds aren't 'better' at hatching eggs. Instead, birds living today and oviraptors have a very different way of incubation or, more specifically, brooding," Yang pointed out. "Nothing is better or worse. It just depends on the environment."
The researchers caution that their results are based on a reconstructed nest and modern environmental conditions, which differ from those of the Late Cretaceous. These differences could influence the findings. They also note that oviraptors likely had longer incubation periods than modern birds.
Even with these limitations, the study provides new insight into how oviraptors may have cared for their eggs. By combining physical models with simulations, the work opens new possibilities for studying dinosaur reproduction.
"It also truly is an encouragement for all students, especially in Taiwan," concluded Yang. "There are no dinosaur fossils in Taiwan, but that does not mean that we cannot do dinosaur studies."
