Scientists from Argentina, the United States, and China have uncovered the first known fossil with air pockets in Alvarezsaurid, a feature previously unseen in this type of dinosaur.
They mentioned this in their paper published in the open-access journal PLOS ONE. The discovery took place in the Allen Formation, a well-known fossil site in Argentina’s Río Negro Province. The fossils belong to a family of fast-moving dinosaurs called Alvarezsauridae and are estimated to be around 70 million years old.
What are Alvarezsaurid dinosaurs?
Alvarezsaurids were small, bird-like dinosaurs known for their unique body shapes. They had long legs and very short arms, with one strong claw likely used for digging or tearing into insect nests. Their heads were small and light, with tiny teeth that suggest they did not eat large prey. Some scientists believe they mostly fed on insects like termites.
Their long tails helped them balance while running, and their body shape suggests they could move quickly. They lived during the Late Cretaceous period and were found in different parts of the world, including Asia and South America.
Bird-like features evolved in dinosaurs
Even though they looked like birds in some ways, researchers had not found air pockets in their bones until now. This discovery brings them one step closer to understanding how bird-like features evolved in dinosaurs.
The study also highlights the importance of CT scanning in studying small dinosaur bones. Because air pockets and blood vessel paths can look similar, high-quality scans are needed to tell them apart.
The bones were found in different sizes, suggesting they came from more than one dinosaur. The most complete fossil, named Bonapartenykus, is now kept at the Carlos Ameghino Museum in Cipolletti City. Other bones from the same site are stored at the Patagonian Museum of Natural Sciences in General Roca.
To examine the bones, researchers used CT scans, similar to those used in hospitals to see inside the human body. These scans revealed tiny air spaces throughout the skeleton, even in parts as far down as the tail, which surprised scientists, who had not expected to find air pockets in these bones.
Variation in air pockets
The amount and location of air pockets varied from bone to bone. Some had more air space than others, with no distinct pattern. In some cases, bones showed holes on the outside but were solid inside. This led researchers to conclude that external features alone are insufficient to determine whether a bone contains air pockets.
Until now, air-filled bones were only found in other dinosaur groups and flying reptiles. Today, birds are the only living animals with this trait. These air pockets help birds remain lightweight, breathe more efficiently, and regulate their temperature better. Scientists believe ancient dinosaurs may have developed this feature for the same reasons.
Lighter bones would have helped dinosaurs move more easily and use less energy. Researchers think this new find may mean air-filled bones were more common in dinosaurs than previously thought.
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