"Superlungs" gave dinosaurs the energy they needed to run and fight

In the oxygen-poor air of the Mesozoic era, nothing could have been very fast. But Velociraptors could run 64 kilometers per hour. According to a new study, their secret weapon: very effective bird lungs, which would have provided a constant supply of oxygen. This unique adaptation could give all the dinos a step ahead of their competitors.

Biologists have long known that birds, which descend from a branch of extinct dinosaurs, possess an unusual and sophisticated respiratory system that allows motorized flight. But palaeontologists have long wondered if these superlungs only appeared in birds or earlier in dinosaurs.

Unlike humans and other mammals, whose lungs dilate and swell, the lungs of birds are rigid. Special airbags along the lungs lift heavy objects, pumping air through the lungs, where oxygen is diffused into the bloodstream. The lungs are attached to the vertebrae and ribs, which form the "ceiling" of the rib cage, helping to keep the lungs still. A connector called the costo-cerebral joint, where the ribs and vertebrae meet, provides additional support. This configuration allows a continuous flow of oxygen and requires less energy than the inflation and deflation of the lungs. It also allows palaeontologists studying fossils to learn a great deal about the lungs by examining the bones around them.

Paleobiologists Robert Brocklehurst and William Sellers of the University of Manchester in the United Kingdom and biologist Emma Schachner of Louisiana State University in Baton Rouge have turned to computer models. They compared the shapes of skeletal elements such as vertebrae and ribs of various species of birds and non-avian dinosaurs.

Many dinosaurs, including therapies like Velociraptor and Spinosaurus, a large carnivorous dinosaur, had similar lung architecture to birds, the team said today. Royal Society Open Science. These dinosaurs sported a costo-cerebral joint and a bird-like osseous "ceiling" that helps keep the lungs rigid.

The team concludes that all this suggests that dinosaurs have the same type of effective respiratory organs as birds. These superlungs can help explain why dinosaurs have managed to dominate and spread, despite the thin air of Mesozoic, says Brocklehurst. At the time, the air contained only 10 to 15% oxygen, compared to 20% today.

Jingmai O 'Connor, paleontologist at the Institute of Paleontology and Paleoanthropology of Vertebrates of the Beijing Chinese Academy of Sciences, explains the work. "The birds are really strange compared to all the other animals," she says. "They have this very advanced breathing system, [and] We've always wondered, "How did it evolve?" Now, it seems likely that the superlungs first developed in dinosaurs, then only to allow powered flight in birds, he said. -she.

But O & # 39; Connor adds that it's not because a fossil has the bone structure of a bird-shaped lung that it actually has. Finding the lung tissue, which is almost never preserved, would be the solution. She described what could be the first preserved lungs found in a bird fossil at the annual meeting of the Society of Vertebrate Paleontology in Albuquerque, New Mexico, last week, and in an article in the Proceedings of the National Academy of Sciences yesterday. In this 120 – million – year – old dove – sized Chinese bird, she and her team noted that, even though the presumed lungs were sophisticated, the skeletal structure around them was primitive, suggesting that bones and soft tissues could not evolve at a constant rate.

However, not everyone is sure that O> Connor's bird organs are really lungs. The structures could be a mineral artifact, speculates Corwin Sullivan, a paleontologist from the University of Alberta in Edmonton, Canada, who studies the evolution of avian respiratory systems. But even if it was so, the specimen is "absolutely fascinating".

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More information:
Robert J. Brocklehurst et al. Vertebral morphometry and lung structure in non-avian dinosaurs Royal Society Open Science (2018). DOI: 10.1098 / rsos.180983

Xiaoli Wang et al. Archaeorhynchus preserving important soft tissues, including probably fossilized lungs, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073 / pnas.1805803115