A team of researchers from Goethe University Frankfurt, Germany, has made an interesting discovery about Troodon, a dinosaur closely related to modern birds. Despite being warm-blooded, or endothermic, Troodon’s reproductive system was similar to that of modern reptiles.
Using a new method, the scientists were able to accurately determine the temperature at which the egg’s carbonate shell was formed. They also found that Troodon laid between 4 and 6 eggs per clutch, with several females laying their eggs in communal nests.
Troodon was a theropod, a group of dinosaurs that evolved into birds. The carnivorous dinosaur roamed North America around 75 million years ago and had some bird-like features such as hollow and light bones. Although Troodon had fully developed feathery wings, it was too large to fly and instead relied on its speed and strong claws to catch prey.
The eggs laid by Troodon females were similar in shape and color to those of modern birds and were found half-buried in the ground, suggesting that the dinosaurs sat on them to brood. The researchers from Goethe University Frankfurt used a method called “dual clumped isotope thermometry” to examine the calcium carbonate in the eggshells and determine the temperature at which they were formed.
According to a recent study, Troodon eggshells were produced at temperatures ranging from 42 to 30 degrees Celsius. Lead author of the study, Mattia Tagliavento, explains that this indicates that Troodon had a body temperature of 42°C and was capable of reducing it to 30°C, similar to modern birds.
The researchers compared the isotopic compositions of Troodon eggshells with those of reptiles, such as crocodiles, alligators, and various species of turtles, as well as modern birds, including chickens, sparrows, wrens, emus, kiwis, cassowaries, and ostriches. They found that reptile eggshells had isotopic compositions that matched the surrounding environment’s temperature, suggesting that these animals were cold-blooded and that their egg formation occurred slowly.
In contrast, birds left a non-thermal signature in their eggshell isotopic composition, indicating that eggshell formation happened very quickly. Tagliavento suggests that this rapid production rate is linked to the fact that birds have a single ovary and can only produce one egg at a time, necessitating a quicker production process.
The research team’s comparison of Troodon eggshells with those of reptiles and modern birds showed that Troodon’s reproductive system was more similar to reptiles than birds. Troodon did not show the isotopic composition typical of birds, which indicates that eggshell formation happened slower than in birds. The researchers concluded that Troodon laid 4 to 6 eggs per reproductive phase, even though large communal nests containing up to 24 eggs have been found. This suggests that Troodon females may have laid their eggs in communal nests, similar to modern ostriches. Jens Fiebig, one of the study’s authors, commented that the dual clumped isotope method, originally developed for reconstructing past surface temperatures, can also help study the evolution of carbonate biomineralization throughout Earth’s history. The study is published in the Proceedings of the National Academy of Sciences.