CHICAGO -- Tyrannosaurus rex may have had a sedentary cousin that might better have been called Ty-sit-osaurus.
That's the finding of Purdue University researcher Richard Hengst, who studies the physiology of dinosaurs to determine the efficiency of their breathing systems.
Hengst, a biologist at Purdue's North Central campus, found that while all early dinosaurs -- those dating back about 220 million years -- breathed inefficiently, dinosaurs that lived only 70 million to 65 million years ago had a much-improved system, resembling that of modern mammals.
However, the rate of improvement in respiratory capabilities differed significantly between the South American and North American dinosaurs, with the southern dinosaurs lagging behind their northern relatives in aerobic fitness for tens of millions of years.
"Whereas 140 million year ago, the Argentine dinosaurs breathed only slightly more efficiently than their more primitive ancestors, the North American dinosaurs of the same age had vastly improved their technique," he says. "The South Americans caught up with their northern relatives only in the later Cretaceous, or about 70 million years ago."
He will present his findings Saturday (10/11) during the annual meeting of the Society of Vertebrate Paleontologists in Chicago.
In his study, Hengst looked at how the ribs were attached to the vertebral column to determine the efficiency of the respiratory systems in a number of carnivorous theropods, a class of flesh-eating dinosaurs that walked mainly on their hind legs and included Tyrannosaurus rex.
By analyzing how the ribs pivoted around two prominent points, and studying how the ribs that make up the chest were aligned on the vertebrae, Hengst was able to determine how the dinosaurs' ribs moved during breathing.
"The more efficiently the chest expanded, the more air the animal could take in and therefore the more aerobic it could be," he says.