The hollow bones of dinosaurs were formed in three independent evolutionary processes. article about it published in Scientific Reports.
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 in them. This feature has been inherited from birds, which diverged from dinosaurs because they could fly. Additionally, less dense bones with more air gave dinosaurs and pterosaurs more dexterity for hunting, running and fighting, as well as more oxygen circulating in their blood. Not only did they need less energy, they also cooled the body more efficiently. Scientists are interested in how exactly such an evolutionary adaptation might have arisen.
Tito Aureliano of the University of Campinas and his colleagues examined the fossilized bones of three Brazilian species that lived during the Late Triassic period (about 233 million years ago), when the dinosaurs appeared. All the bones were found in Rio Grande do Sul, Brazil’s southernmost state, in recent years. Examining specimens from different groups and 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 common in geologically newer (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 that became the largest animals to walk on the planet. Third was the herrerasaurid, one of the first carnivorous dinosaurs whose genetic line was rapidly interrupted.
The study was carried out using computed tomography, which makes it possible to see all the cavities, including veins, arteries and bone marrow openings, without disturbing the structure. At the same time, none of them can serve as pneumatic chambers through which air can pass. A study published in 2021 showed that another dinosaur lineage, the ornithischians, also lacked structures to house air sacs in the early stages of evolution.
Based on this, the authors of the new study conclude that the air sacs developed independently in each group. “We found that no common ancestor had this feature. All three groups must have developed air sacs independently of each other. The Triassic was very hot and dry. The place now called Rio Grande do Sul was in the heart of the supercontinent Pangea, far from the sea. In this environment, blood The more oxygen circulating, the more efficiently it will cool the body, and it certainly provides such a powerful advantage that it has evolved independently of each other at least three times,” say the scientists.
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