(ORDO NEWS) — The hollow bones of dinosaurs formed in three independent evolutionary processes.
Many dinosaurs reached gigantic sizes and weights, much larger than those of modern elephants.
In order to achieve great growth and not break under their own weight, the bones of many of them became lighter – air sacs formed inside them.
This feature was inherited by birds that separated from dinosaurs, thanks to which they are able to fly.
In addition, less dense bones containing more air gave dinosaurs and pterosaurs more oxygen circulating in their blood, as well as greater dexterity for hunting, running and fighting.
Not only did they require less energy, but they also cooled the body more efficiently. Scientists are interested in how exactly such an evolutionary adaptation could have arisen.
Tito Aureliano of the University of Campinas and colleagues analyzed the fossilized bones of three Brazilian species that lived during the Late Triassic period (about 233 million years ago), when dinosaurs appeared.
All bones have been found in recent decades in Rio Grande do Sul, the southernmost state of Brazil.
The study of specimens belonging to different groups and dating from an early stage of their evolution allows us to understand how certain characters developed.
In this case, the researchers were looking for evidence of air sacs, which were common in geologically more recent (and more studied) species such as tyrannosaurs or velociraptors.
The fossils belonged to three species: Buriolestes schultzi, Pampadromaeus barberenai and Gnathovovorax cabreirai.
The first two were sauropodomorphs, long-necked dinosaurs, which then became the largest animals ever to walk the planet.
The third was the herrerasaurid, one of the first carnivorous dinosaurs, whose genetic line was quickly interrupted.
The study was carried out using computed tomography, which made it possible to see all cavities without destroying the structure, including openings for veins, arteries and bone marrow.
At the same time, none of them could serve as pneumatic chambers through which air could pass.
A study published in 2021 also showed that another line of dinosaurs, the ornithischians, also lacked structures in the early stages of evolution that could house air sacs.
Based on this, the authors of the new work conclude that the air sacs developed independently in each group. “We found that no common ancestor had this trait.
All three groups must have developed air sacs independently. The Trias was very warm and dry. What is now called Rio Grande do Sul was far from the sea, in the heart of the supercontinent Pangea.
In this environment, more oxygen circulating in the blood would cool the body more efficiently and would certainly provide an advantage so strong that it has evolved at least three times independently of each other, ”the scientists summarize.
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