A new study conducted at the University of Calgary looked into the porosity of dinosaur eggs and found that the nesting habits of some dinosaurs may have foreshadowed the nesting habits of birds.
Dinosaur nesting materials and nest structures are not typically preserved in fossil records, experts said. This lack of data had made it extremely difficult for scientists in the past to know how dinosaurs built their nests and how dinosaur eggs were incubated.
Now, in a paper featured in the journal PLOS ONE, Kohei Tanaka, a doctoral student, demonstrated the link between the porosity of eggshells and the different types of dinosaur nesting.
Tanaka, working under the guidance of Assistant Professor Darla Zelenitsky, carefully studied the eggshell porosity of 30 various species of dinosaurs. Tanaka compared his findings to the eggshell porosity of 120 species of crocodiles and birds which are considered to be the descendants of dinosaurs.
The study found that primitive dinosaurs incubate their eggs by burying them in the ground in a similar way that crocodiles bury theirs, while more advanced dinosaurs exposed their eggs in open nests.
Tanaka explained that birds that brood incubate their eggs in open nests and their eggshells tend to have low porosities compared to megapode birds and crocodiles that bury their eggs.
Most dinosaurs such as the long-necked sauropods, plant-eating ornithischians, and primitive theropods had produced eggs with high porosity, the study said.
Tanaka said the eggs of primitive carnivorous dinosaurs and long-necked sauropods were highly porous to allow for the distribution of carbon dioxide and oxygen while allowing water vapor to escape.
The level of egg porosity seemed to reduce among small meat-eating dinosaurs, he said.
Meanwhile, the eggshells of advanced dinosaurs such as theropods, which are the ancestors of modern birds, indicated low porosity. It means that these eggs were incubated in the nest, although some open-nesters still partly buried their eggs, scientists said.
Tanaka believes the findings of the study could support the idea that the only creatures that are capable of incubating are warm-blooded ones.
Tanaka and his co-authors suggested that it was not until modern-looking birds came to be that nests were fully exposed, and that as dinosaurs evolved into birds, so did their nesting habits and incubation style.
Meanwhile, the next step for the researchers is to study the number of days it usually takes for dinosaur eggs to hatch.
"We'd like to know how nesting behavior, or styles of nesting, changed through evolution from reptiles, to dinosaurs, and finally birds," added Tanaka.
