Chemical analysis of the Jurassic period fossil teeth from two sauropods -- long-tailed, long-necked dinosaurs that rank among the largest land animals ever to roam the Earth -- showed they were about as warm as most modern mammals.
But they also were cooler than some experts had predicted for animals of such gigantic size.
The findings from a team led by researchers at the California Institute of Technology were published Thursday in an online edition of the journal Science.
"This is like being able to stick a thermometer in an animal that has been extinct for 150 million years," said Robert Eagle, an evolutionary biologist and post-doctoral scholar at Caltech who was lead author of the report.
The study supports a growing body of research suggesting dinosaurs were more active and energetic than scientists originally believed.