Oviraptors May Have Needed the Sun to Hatch Their Eggs

New experiments indicate that bird-like oviraptorid dinosaurs could not completely warm their eggs with body heat alone, instead combining brooding with solar heat in semi-open nests.

An artist’s impression of Huanansaurus ganzhouensis. Image credit: Chuang Zhao.

“We show that the difference in oviraptor hatching patterns was driven by the relative position of the incubating adult to the eggs,” said Dr. Tzu-Ruei Yang, a paleontologist at the National Taiwan Museum of Natural Sciences.

“In addition, we obtained an estimate of the incubation efficiency of oviraptors, which is much lower than that of modern birds,” said Chun-Yu Su, a researcher at Washington High School.

In the study, researchers simulated the brooding behavior of Heyuannia huangia species of oviraptorid dinosaur that lived in what is now China during the late Cretaceous, between 70 and 66 million years ago.

Estimated to be around 1.5 m long and weighing around 20 kg, it built semi-open nests consisting of several egg rings.

The trunk of the incubating oviraptor was made from polystyrene foam and wood for the skeletal frame and cotton, bubble wrap, and fabric for the soft tissues.

The eggs were cast from casting resin. In both clutches used in the experiments, eggs were arranged in double rings based on real oviraptor clutches.

“Part of the difficulty lies in realistically reconstructing oviraptor incubation,” Su said.

“For example, their eggs don’t look like those of any living species, so we invented resin eggs to get as close as possible to real oviraptor eggs.”

Artistic depiction of an oviraptorosaur, hadrosaur, and tyrannosaur from the Late Cretaceous in central China. Image credit: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.

When the team conducted experiments to determine whether the presence of a brooding adult in the clutch or different environmental circumstances could impact hatching patterns, they found that at colder temperatures, where a brooding adult attended the clutch, the temperatures of eggs in the outer ring differed by up to 6 degrees Celsius, which could have resulted in asynchronous hatching, a pattern in which eggs in the same nest hatch. at different times.

In warmer conditions, the temperature difference of eggs in the outer ring was only 0.6 degrees Celsius, suggesting that oviraptors living in warmer conditions may have exhibited a different asynchronous hatching pattern, because they were able to use the Sun as an additional and powerful heat source.

“Large dinosaurs are unlikely to have sat atop their broods. It is assumed that they used heat from the sun or the ground to hatch their eggs, like turtles,” Dr Yang said.

“Since oviraptor broods are open to the air, the heat from the Sun probably mattered much more than the heat from the ground.”

The researchers also studied how the incubation efficiency of oviraptors compares to that of modern birds.

Most birds use thermoregulatory contact incubation, where adults sit directly on eggs to transfer heat.

Thermoregulatory contact incubation requires three prerequisites: the adult bird must be in contact with each egg, be the primary heat source, and maintain all eggs within a constrained temperature range, which oviraptors did not meet.

“Oviraptors may not have been able to perform thermoregulatory contact incubation like modern birds do,” Su said.

“Instead, these dinosaurs and the Sun could have been co-incubators – a less efficient incubation behavior than that displayed by modern birds.”

“Yet the combination of adult incubation and an ambient heat source – perhaps a behavioral adaptation associated with the evolution from buried to semi-open nests – is not necessarily worse.”

“Modern birds are not ‘better’ at incubating eggs,” Dr. Yang said.

“Instead, birds living today and oviraptors have a very different way of incubation or, more precisely, brooding.”

“Nothing is better or worse. It just depends on the environment.”

The results were published in the journal Frontiers of ecology and evolution.

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Chun Yu Su and others. 2026. Heat transfer in a realistic brood reveals lower incubation efficiency of oviraptorid dinosaurs than that of modern birds. In front. Ecol. Evol 14; doi: 10.3389/fevo.2026.1351288