In the oxygen-poor air of the Mesozoic, nothing could have moved very fast. But Velociraptors could run 64 kilometers per hour. Her secret weapon: super-efficient, bird-like lung, which according to a new study would have pumped a constant supply of oxygen. This unique adaptation may have given all Dinos an edge over their competitors.
Biologists have long known that birds that come from a branch of extinct dinosaurs have an unusual, sophisticated respiratory system that enables powered flight. Paleontologists have long debated whether these superlungs occurred only in birds or earlier in dinosaurs.
In contrast to humans and other mammals whose lungs expand and deflate, avocets are rigid. Special air sacs next to the lungs, instead, do the heavy lifting and pump air through the lungs, where the oxygen diffuses into the bloodstream. The lungs are attached to the vertebrae and ribs that form the "ceiling" of the rib cage – all of which helps to keep the lungs stationary. A connector, the so-called Costovertebralgelenk, on which the ribs and vertebrae meet, offers further support. This design allows a continuous flow of oxygen and requires less energy than the inflation and deflation of the lungs. It also allows paleontologists to study fossils, to learn much about the lungs by examining the bones around them.
To find out when these superlions developed, paleobiologists Robert Brocklehurst and William Sellers of the University of Manchester in the UK and biologist Emma Schachner of the Louisiana State University at Baton Rouge turned to computer models. They compared the shapes of skeletal features such as vertebrae and ribs in a number of avian and non-avian dinosaur species.
Many dinosaurs, including therapists such as Velociraptor and Spinosaurus a large carnivorous dinosaur, had similar lung architecture to birds, the team reported today in Royal Society Open Science . These dinosaurs had a costo-tetral joint and the birdlike bone "blanket" of the vertebrae and ribs that kept the lungs stiff.
All this suggests that dinosaurs have the same kind of efficient respiratory system as birds, the team concludes. These superlions could help explain why dinosaurs were able to dominate and spread, despite the barren air of the Mesozoic, says Brocklehurst. At that time, the air was only 10% to 15% oxygen, compared to 20% today.
The work shows how exceptional lungs have developed, says Jingmai O & Connor, paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing. "Birds are really funny compared to all other animals," she says. "You have this sophisticated respiratory system, [and] we've always wondered, how did that evolve?" Now it seems likely that superlungs were first developed in dinosaurs and later developed to support powered flight in birds, she says:
But O & # 39; Connor adds just because a fossil's bone structure is similar to bird-like lungs does not necessarily mean that it actually has such lungs. Finding lung tissue that is almost never preserved would be the rash. She described last week the first preserved lung found in a bird fossil at the annual meeting of the Society of Vertebrate Paleontology in Albuquerque, New Mexico, and in a newspaper in the Proceedings of the National Academy of Sciences . In this 120-million-year-old, dove-sized bird from China, she and her team found that although the putative lungs were highly developed, the skeletal structure around them was primitive, suggesting that bones and soft tissue could not develop in lockstep. Not all are sure that O & # 39; Connor's bird organs really are lungs. The structures could be a mineral artefact, speculates Corwin Sullivan, a paleontologist at the University of Alberta in Edmonton, Canada, who studies the evolution of the respiratory tract of birds. But even if, he says, the copy is "absolutely fascinating."