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Dinosaur eggshell analysis: Bird-like Troodon laid 4 to 6 eggs in a communal nest


Several female Troodon lay their eggs in communal nests. Credit: Alex Boersma/PNAS

An international research team led by Goethe University Frankfurt, Germany, determined that Troodon, a dinosaur very close to modern birds, was a warm-blooded (endothermic) animal, but had a reproductive system similar to that of modern reptiles.

The scientists applied a new method that allows for an accurate determination of the temperature at which the egg’s carbonate shell forms. Moreover, the researchers showed that Troodon laid 4 to 6 eggs per clutch. Nests with up to 24 Troodon eggs were found, scientists concluded that several Troodon females laid their eggs in communal nests.

In millions of years and with a long series of small changes, evolution has shaped the particular group of dinosaurs, theropods, into the birds we see flying around the planet today. In fact, birds are the only descendants of dinosaurs to survive the catastrophic extinction 66 million years ago that ended the Cretaceous period.

Troodon was such a theropod. The carnivorous dinosaur was about two meters long and inhabited the vast semi-arid landscapes of North America about 75 million years ago. Like some of its dinosaur relatives, Troodon presented some bird-like features such as hollow, light bones. Troodon walked on two legs and had fully developed feathery wings, but its relatively large size precluded it from flying. Alternatively, it may have run very fast and grabbed its prey using its powerful claws.

Troodon females laid eggs that looked more like the asymmetric eggs of modern birds than those of round reptiles, the oldest relatives of all dinosaurs. These eggs were colored and found half-buried in the ground, likely allowing Troodon to sit and think about them.

An international team of scientists led by Mattia Tagliavento and Jens Fiebig of Goethe University in Frankfurt, Germany, examined the calcium carbonate of some well-preserved Troodon eggshells. The researchers used a method Fiebig’s group developed in 2019 called “coupled isotope cluster thermometry.”

Using this method, they can measure how closely the heavy isotopes (isotopes) of oxygen and carbon clump together in carbonate minerals. The spread of isotopic clustering, which depends on temperature, has made it possible for scientists to determine the temperature at which carbonates crystallize.

Analyzing eggshells from Troodon, the research team was able to determine that the eggshells were produced at temperatures of 42 and 30 degrees Celsius. Mattia Tagliavento, lead author of the study, explains, “The isotopic composition of Troodon eggshells provides evidence that these extinct animals had a temperature of 42°C, and that they managed to reduce it to around 30°C, like modern birds.”

The scientists then compared the isotopic compositions of the eggshells of reptiles (crocodile, alligator, and various species of turtle) and modern birds (chicken, sparrow, wren, emu, kiwi, cassowary and ostrich) to understand whether Troodon was more closely related to birds or reptiles. . They revealed two different isotope patterns: Reptile eggshells have isotopic compositions that correspond to the temperature of the surrounding environment. This goes with these animals being cold-blooded and slowly forming their eggs.

However, the birds leave a so-called non-thermal signature in the isotopic composition, which indicates that eggshell formation occurs very rapidly. “We think that this high rate of production is related to the fact that birds, unlike reptiles, have one ovary,” says Tagliavento. “Since they can only produce one egg at a time, birds have to do it more quickly.”

When comparing these results to Troodon eggshells, the researchers didn’t discover the typical isotopic composition of birds. Tagliavento is convinced: “This indicates that Troodon formed its eggs in a manner more comparable to modern reptiles, meaning that its reproductive system was still composed of two ovaries.”

The researchers finally combined their findings with existing information regarding body weight and eggshells, and concluded that Troodon only produced 4 to 6 eggs at each reproductive stage. “This observation is particularly interesting because Troodon nests are usually large, containing up to 24 eggs,” Tagliavento explains. “We think this is a strong suggestion that Troodon females laid their eggs in communal nests, a behavior we observe today among modern ostriches.”

These are very exciting results, comments Jens Fiebig, “Originally, we developed the coupled isotope pooling method to accurately reconstruct Earth’s surface temperatures in past geologic epochs. This study demonstrates that our method is not limited to temperature reconstruction, it also presents an opportunity to study How Biocarbonate Minerals Evolved Throughout Earth’s History.”

The work has been published in the journal Proceedings of the National Academy of Sciences.

more information:
Tagliavento, Mattia. Evidence for heterothermic and reptilian-like eggshell mineralization in Troodon, non-avian theropods, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2213987120

Provided by Goethe-University Frankfurt am Main

the quote: Dinosaur Eggshell Analysis: Bird-like Troodon Laying 4 to 6 Eggs in a Communal Nest (2023, April 3) Retrieved April 3, 2023 from https://phys.org/news/2023-04-analysis-dinosaur- eggshells-bird-like-troodon.html

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