First evidence of 'hollow bones' found in dinosaurs, just like modern birds

Modern birds have air-filled cavities in their bones to reduce weight for flight. Interestingly, this feature has also been discovered in dinosaur fossils.

A new study of alvarezsauridae fossils has identified these same bone features in creatures that roamed the Earth nearly 70 million years ago.

Experts studying these slender dinosaurs uncovered evidence of hollow channels that link to their respiratory systems.

The results suggest that pneumaticity might have been more common in theropod dinosaurs than previously thought.

This work was led by The Patagonian Museum of Natural Sciences in Roca, and was founded as a project by the Patagonian Foundation of Natural Sciences. Researchers collaborated across Argentina and China to piece together details of these unusual bones.

Dinosaur bones were hollow

Bird skeletons stand out for their lightweight build. Many have air sacs that extend into bones, helping to manage body temperature, improve respiratory functions, and reduce overall mass.

Scans of these new fossils indicate that such air sacs already existed in some dinosaur lineages.

Paleontologists suggest this adaptation might have provided other benefits, particularly in oxygen circulation.

Hollow bones helped dinosaur breathing

Researchers have long known that certain dinosaur groups had air pockets in their skeletons. Yet the extent of these cavities in theropod dinosaurs has been debated.

CT scans of the dinosaur fossil vertebrae uncovered interconnected voids that likely connected to respiratory structures.

This structural pattern resembles what is seen in living birds, though the ancient dinosaur bones differ in shape and size.

Surprising tail anatomy

One unexpected twist came from the tail region. Internal air spaces showed up as far back as the middle segments, hinting at a more widespread distribution of air pockets than is found in some other species.

Specialists in dinosaur fossils and biology have typically focused on the neck and torso regions for signs of air sacs.

However, seeing as the air sacs extend far into the tail, this raises fresh questions about how these creatures breathed and moved.

Random variability in bone cavities

Another puzzle emerged when the team compared separate specimens of different sizes. They found uneven patterns of diverticula within the same type of vertebrae, suggesting no clear progression of these air pockets.

“This study is an important first step that paves the way for future studies to uncover the extent of pneumatic invasion among alvarezsauridaes, and its macroevolutionary implications,” explained J. G. Meso from The Patagonian Museum of Natural Science.

The authors described this uneven distribution of hollow spaces in dinosaur bones as a seemingly random process that might relate to blood vessel pathways.

New directions in dinosaur research

Scholars comparing these findings to those of other species note that air cavities might show up in surprising places once larger fossil datasets are examined.

Some suspect this adaptation appeared in different dinosaur families at various points, rather than following a steady evolutionary path.

With more advanced imaging, experts hope to learn if certain groups gained or lost these hollow spaces over time. This approach could reveal unexpected links between distant branches of the dinosaur family tree.

Dinosaur bones changed with evolution

Lightweight skeletal features might have enhanced efficiency, but no one knows if they aided speed, temperature control, or other factors.

Studies of bird flight have shown that reduced bone mass can help modern species, though alvarezsauridaes did not soar.

Further research might clarify whether these air-filled bones played a role in daily activity or growth. Specialists also want to explore how these structures evolved among predators, scavengers, and other lifestyles within coelurosaurians.

Scientists remain cautious about comparing ancient air sacs to those of living birds. Different theropod families likely followed various paths to lighten their bones and enhance respiratory function.

Some paleontologists propose that future CT analyses of more fossils could confirm if these features evolved multiple times. Each new discovery brings fresh insights into how dinosaurs thrived in unique environments.

Future research may reveal complex bone cavities in species other than dinosaurs. Ongoing studies will broaden our view of how dinosaurs thrived.

The study is published in the journal PLOS One.

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