Bird-like Troodon dinosaurs shared communal nests about 75 million years ago

The team examined well-preserved Troodon egg shells for this new study. They focused on the calcium carbonate shredded by the eggshells using a technique known as "dual-clumped isotope thermometry."

Using this technique, they could determine the temperatures and speed at which the eggs were produced. 

The findings revealed that eggshells were produced at around 107.6°F (42°C), which later dropped to 86°F (30°C). “The isotopic composition of Troodon eggshells provides evidence that these extinct animals had a body temperature of 107.6°F (42°C) and that they were able to reduce it to about 86°F (30°C), like modern birds,” said Mattia Tagliavento, the lead author of the study, in a statement. 

This suggests that Troodons were endotherms, or warm-blooded creatures capable of self-regulating their body temperature. Unlike other dinosaur species, which buried their eggs underground, they were able to brood their eggs.

Shared their nest 

The egg shells were also compared to those of modern birds and reptiles. This allowed the team to determine whether Troodon was more closely related to birds or reptiles.

Tagliavento added, “Troodon formed its eggs in a way more comparable to modern reptiles, and it implies that its reproductive system was still constituted of two ovaries.” 

They had a slower egg formation process than birds with one ovary. Troodon, like reptiles, produced only 4 to 6 eggs per reproductive phase.

This observation contributed to the finding that the species shared nests, as experts discovered large Troodon nests containing up to 24 eggs. “We think this is a strong suggestion that Troodon females laid their eggs in communal nests, a behavior that we observe today among modern ostriches,” said Tagliavento. 

The study concludes that Troodon was a warm-blooded animal with a reproductive system similar to modern reptiles.

The study has been published in the journal PNAS.

Study abstract:

The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ47and Δ48) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon, modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual-clumped isotope data also reveal physiological differences in the reproductive systems between Troodon, reptiles, and birds.