HARVARD GAZETTE ARCHIVES

New research shows that fierce meat-eating dinosaurs like this 67-million-year-old Majungatholus atopus had lungs not all that different from a sweet-singing, crumb-grabbing sparrow. (Nicolle Rager Fuller/National Science Foundation)

What could the fierce dinosaur Tyrannosaurus rex and a modern songbird such as the sparrow possibly have in common? Their pulmonary systems may have been more similar than scientists previously thought, according to new research from Harvard University and Ohio University.

Though some scientists have proposed that predatory dinosaurs had lungs similar to crocodiles and other reptiles, a new study published in this week's issue of the journal Nature suggests the ancient beasts boasted a much bigger, more complex system of air sacs similar to that in today's birds. The finding is one of several studies in recent years to paint a new, more avianlike portrait of meat-eaters such as T. rex: The creatures may have had feathers, incubated their eggs, grown quickly, and perhaps even breathed like birds.

"This paper shows that predatory dinosaurs had a pulmonary system with the potential to support elevated rates of metabolism, higher than what we typically associate with 'cold-blooded' reptiles," said co-author Leon P.A.M. Claessens, who received a Ph.D. from Harvard in organismic and evolutionary biology last month and will join the faculty at the College of the Holy Cross in Worcester, Mass., this fall. "The pulmonary system of meat-eating dinosaurs such as T. rex in fact shares many structural similarities with that of modern birds, which, from an engineering point of view, may possess the most efficient respiratory system of any living vertebrate inhabiting the land or sky."

Some ancient dinosaurs (bottom) apparently had lungs not too different from ducks (top). In both breathing systems, air passes through the lungs twice, increasing metabolism and making the dinosaurs warm-blooded rather than cold-blooded. (Zina Deretsky/National Science Foundation)

"What was once formally considered unique to birds was present in some form in the ancestors of birds," said Patrick O'Connor, an assistant professor of biomedical sciences at Ohio University's College of Osteopathic Medicine and lead author on the study, which was funded in part by the National Science Foundation.

The researchers visited museums in New York, Berkeley, Chicago, Washington, Pittsburgh, Berlin, and London to examine the bones of ancient beasts, and also studied a 67-million-year-old dinosaur, Majungatholus atopus, that O'Connor discovered in Madagascar as a graduate student in 1996. They compared the dinosaur skeletons with those of modern birds to draw comparisons of how the soft tissues in the dinosaurs may have been structured.

Birds have long fascinated biologists because of their unusual pulmonary system. Pulmonary air sacs prompt air to pass through the lungs twice during ventilation. This system also creates holes in the skeleton of birds, which has led to a popular notion that birds have "air in their bones," O'Connor said.

The new study, which examined how the air system invades the skeleton in areas such as the neck, chest, and hips, finds similarities between the vertebral column of dinosaurs and birds that point to a common soft tissue system as the culprit. Though probably not identical to living birds, "it's nothing like the crocodile system as we know it," O'Connor said.

In birds, this anatomical configuration increases the gas exchange potential within the lungs, boosting metabolism and creating warm-bloodedness. O'Connor and Claessens point out, however, that the new study doesn't clearly peg predatory dinosaurs as habitually warm-blooded animals. The creatures probably had a more complex strategy, falling somewhere between what scientists define as cold- and warm-blooded. It appears that these animals had the pulmonary machinery for enhanced gas exchange, which would have pushed them closer to being warm-blooded creatures.

Previous research that pointed to a more crocodile-like pulmonary system was based on a study of two dinosaur skeletons encased in rock. O'Connor and Claessens have expanded on that research by studying a broader collection of dinosaur skeletal remains, and are the first to integrate both anatomical and functional studies of modern birds as models of how the ancient creatures' air sacs were structured.

The two scientists are part of a reinvigorated movement of researchers who are examining dinosaur bones and comparing them with modern animals to learn more about the anatomy of these extinct beasts.

"Patrick O'Connor and I have been independently studying the respiratory system in dinosaurs and other extinct groups, together with their living cousins crocodiles and birds, and have seen our research and data converge more and more over the years," Claessens said.

Additional funding for the research came from the Society for Integrative and Comparative Biology, the Society of Vertebrate Paleontology, the Jurassic Foundation, and the S. & D. Welles Research Fund.