It’s sometimes hard to imagine how the planet we call home, with its megalopolis cities and serene farms, was once dominated by dinosaurs the size of buses and five-story buildings. But recent research has helped deepen our understanding of why dinosaurs prevailed: the answer may lie in their special bones, structured like Aero chocolate.
Brazilian paleontologist Tito Aureliano discovered that hollow bones filled with tiny air sacs were so important to the survival of dinosaurs that they evolved independently several times in different lineages.
According to the study, aerated bones evolved in three separate lineages: pterosaurs, technically flying reptiles, and two lineages of dinosaurs – theropods (ranging from the crow-sized Microraptor to the enormous Tyrannosaurus rex) and sauropodomorphs (long-necked herbivores, including Brachiosaurus). The researchers focused on the end of the Triassic period, around 233 million years ago, in southern Brazil.
Every time an animal reproduces, evolution throws random variants into the genetic code. Some of these variants are passed on to offspring and develop over time.
Charles Darwin believed that evolution created “infinitely more beautiful forms”. But some adaptations spontaneously arise over and over again, a bit like being dealt the same hand of cards over and over again. When the same hand keeps appearing, it’s a sign that evolution has found an important and effective solution.
The variant studied by the Brazilian team was the bones of the aerated vertebrae, which would have increased the dinosaurs’ strength and reduced their body weight.
Its regular deliveries from Amazon or other online retailers are packaged in corrugated cardboard, which has the same advantages as aerated bones. It’s light but sturdy.
Corrugated cardboard, or as it was known, pleated paper, was a hugely successful man-made design experiment that is now part of our everyday lives. It was patented in England in 1856 and was initially designed to support top hats, which were popular in Victorian England and the United States at the time.
Three years later, Darwin published his On The Origin Of Species, which outlined how evolutionary traits that create advantages are more likely to be passed on to future generations than variants that do not.
Computed tomography technology allowed Aureliano and his colleagues to peer inside the rock-hard fossils they studied. Without modern technology, it would have been impossible to look inside fossils and detect the alveoli in spinal columns.
The study found that no common ancestors had this trait. All three groups must have developed air pockets independently, and each time in slightly different ways.
The alveoli probably increased the dinosaurs’ blood oxygen levels. The Triassic period had an extremely hot and dry climate. Therefore, more oxygen circulating in the blood would cool dinosaur bodies more efficiently. It would also allow them to move faster.
The air sacs would have supported and reinforced the internal structure of dinosaur bones, while creating a greater attachment surface area for large, powerful muscles. This would have allowed the bones to grow to a much larger size without burdening the animal.
In living birds, aerated bones reduce overall mass and volume while increasing bone strength and stiffness—essential characteristics for flight.
Not only does paleontology tell the story of what Earth might have been like if not for that infamous asteroid, it also helps us learn about the evolution of living creatures.
Echoes of this dinosaur legacy are in many animals alive today. It’s not just long-dead animals that find this kind of adaptation useful. Many species of birds living today rely on hollow bones for flight. Other animals use the air sacs to reinforce and strengthen their large bones and skulls without overloading them.
An excellent example of this is the elephant skull. Inside elephant skulls are large air pockets that allow the animal to move its massive head and heavy tusks without straining its neck muscles.
The human brain is also protected by two layers of hard, compact bone (inner and outer boards) that intersperse a layer of softer, spongy, airy bone known as diploe. This allows our skulls to be light but strong and able to absorb shocks to the skull.
These are examples of convergent evolution where animals are repeatedly faced with the same problem, developing similar – but not always identical – solutions each time. Today’s animals follow the same evolutionary playbook as dinosaurs.
By Sally Christine Reynolds, Principal Scholar in Hominin Paleoecology, Bournemouth University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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