Prehistoric Dinosaur Eggs: Differing Shell Porosity Highlights Evolution Of Nests

The porosity of ancient archosaur eggshells is a proving a bit of a clue about whether dinosaurs lived in covered or exposed nests. Researchers from the University of Calgary, Canada, and colleagues suggest their recent study could help explain the evolution of reproductive behaviors in the dinosaur's modern relatives.

Archosauria, otherwise known as the "ruling reptiles," were a major group of dinosaurs that first emerged during the Permian period 250 million years ago. Modern descendants of the large creatures include birds and crocodilians.

While little evidence of prehistoric nests remains, ancient eggshells are providing unique insight. Based on the fossil record, researchers conclude the reigning reptiles had two general types of nests: open nests that left eggs exposed and covered nests. While the latter of the two nest types were built by individuals that would incubate their eggs using external heat sources, the open nests were built by those that would protect and warm their developing young themselves, according to a news release.

When analyzing different porosities, or the space between grains, of fossil archosaur eggs researchers were able to estimate the type of nest those eggs were originally laid in. In total, more than 120 extinct archosaur species and 29 extinct archosaur taxa was examined for their study. (Scroll to read more...)

So what did they find? It turns out there was a strong correlation between high porosity and incubation by brooding parents. For example, advanced theropods featured high porosity eggshells, suggesting the dinosaurs laid and incubated their eggs in open nests similar to how closely related living birds do today. Other paleontological evidence revealed the open-nesters may have also still partly buried their eggs.

In general, covered nests were used by more primitive dinosaurs, and a transition from covered to uncovered nests may be a result of the need for different nesting locations to avoid predation, flooding and rainfall – or a change in incubation style of dinosaurs during their evolution toward birds.

"Because buried nests needed to be built and incubated on the ground, open nesting and brooding may have allowed advanced theropods -including birds - to incubate eggs in a greater diversity of locations and occasionally away from ground predators, potentially contributing to their evolutionary success," Darla Zelenitsky, assistant professor at the University of Calgary and a world expert in dinosaur eggs and nesting sites, concluded in the university's release.

Their findings were recently published in the journal PLOS ONE.

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