New research reveals dinosaurs used sun to help hatch eggs

By Stephen Beech

Dinosaurs hatched eggs less efficiently than modern birds, according to new research.

The study suggests that – unlike modern birds – the now extinct reptiles may have used the sun’s warmth to help hatch eggs.

Scientists in Taiwan examined the brooding behavior and hatching patterns of bird-like but flightless oviraptors.

The research team also modelled heat transfer simulations of oviraptor clutches and compared the hatching efficiency to modern birds.

To do so, they experimented with a life-sized oviraptor incubator and eggs.

Study senior author Dr. Tzu-Ruei Yang said: “We show the difference in oviraptor hatching patterns was induced by the relative position of the incubating adult to the eggs.”

First author Chun-Yu Su said: “Moreover, we obtained an estimate of the incubation efficiency of oviraptors, which is much lower than that of modern birds.”

The reconstructed oviraptor Heyuannia huangi lived between 70 and 66 million years ago in what is now China.

Estimated to be around 1.5 metres (4.9 feet) long and weighing around 20 kilos (44lbs), it built semi-open nests made up of several rings of eggs.

The incubating oviraptor’s trunk was made from polystyrene foam and wood for the skeletal frame and cotton, bubble paper, and cloth for the soft tissue. Eggs were moulded from casting resin.

In the two clutches used in the experiments, eggs were arranged in double-rings based on real oviraptor clutches.

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

“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.”

The team found that in colder temperatures, where a brooding adult attended the clutch, the eggs’ temperatures in the outer ring differed by up to 6°C, which could have resulted in asynchronous hatching - a pattern where eggs in the same nest hatch at different times.

In warmer conditions, the difference in egg temperatures in the outer ring was just 0.6°C, suggesting that oviraptors living in warmer conditions may have exhibited a different pattern of asynchronous hatching because they could use the sun as an additional, powerful heat source.

Dr. Yang, an associate curator of vertebrate paleontology at Taiwan’s National Museum of Natural Science in Taichung City, said: “It’s unlikely that large dinosaurs sat atop their clutches.

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"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."

The team also investigated how oviraptor incubation efficiency compares to that of modern birds.

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

The research team explained that TCI requires three prerequisites – the adult bird must be in contact with every egg, be the main heat source, and maintain all eggs within a constrained temperature range – which oviraptors didn’t fulfil.

For example, their egg arrangement prevented the adult from making full contact with all eggs in the clutch.

Su said: “Oviraptors may not have been able to conduct TCI as modern birds do.

"Instead, these dinosaurs and the sun may 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 – isn’t necessarily worse."

Dr. Yang said: “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.

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

The team pointed out that their findings, published in the journal Frontiers in Ecology and Evolution, are specific to the reconstructed nest and are limited by the fact that today’s climate does not resemble the Late Cretaceous climate, which may have impacted the results.

They said oviraptors also had a longer incubation period than modern birds.

But the team said the study advances understanding of oviraptor brooding methods through innovative approaches.

Dr. Yang added: “It also truly is an encouragement for all students, especially in Taiwan.

“There are no dinosaur fossils in Taiwan but that does not mean that we cannot do dinosaur studies.”