"When a dinosaur started small and grew large, its body temperature changed dramatically through its lifespan, unlike any animals we know today," Gillooly said. "It increased by about 5 degrees Fahrenheit for species weighing about 661 pounds as adults and nearly 36 degrees for those reaching about 27 tons. This dramatic difference in body temperature between the largest and smallest dinosaurs probably resulted in major differences in how these species lived, because we know a difference of 18 degrees Fahrenheit results in a nearly 300 percent change in rates of population growth, lifespan and population density."
For many years, scientists had assumed that dinosaurs were cold-blooded, or ectotherms, with a slow metabolism that required the sun's heat to regulate temperature. But in the late 1960s, the notion emerged that dinosaurs, like mammals and birds, might have been warm-blooded, or endotherms, with relatively constant, high body temperatures that were internally regulated.
The new findings show that even though dinosaurs were cold-blooded reptiles, large dinosaurs dissipated body heat more slowly, and thus maintained higher, more constant body temperatures similar to today's birds and mammals. The researchers show that this increase in body temperature with size has been observed in modern crocodiles.
"The study is an important contribution to the scientific discussion about dinosaurs, because it is the first that uses evidence directly derived from fossils -- rather than from theoretical models -- to conclude that many of the larger dinosaurs were indeed warm reptiles," said Frank Seebacher, Ph.D., of the School of Biological Sciences at the University of Sydney, who did not take part in
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Contact: John Pastor
jpastor@vpha.health.ufl.edu
352-273-5810
University of Florida
11-Jul-2006