The New York Times has a story about recent T. rex research. There’s been a long running debate about whether dinosaurs were warm or cold blooded – endothermic or exothermic. New research, published recently in the journal Science Advances, adds a little evidence to the warm blooded side.

Scientists at the University of California, Los Angeles, used a geochemistry techniques on fossilized teeth, including two from “Thomas”, a T. rex at the National History Museum of Los Angeles County. They looked at carbon and oxygen bonds in a the T. rex teeth. Bonds of the heavier isotopes act as a paleo-thermometer. More bonds mean the teeth grew at a lower temperature. The analysis yielded a range of 97 to 103 degrees.

For a gut check, they also compared the T. rex teeth to those of ancient crocodilians excavated from the same site Hell Creek Formation in Montana. T. rex measured 97 degrees; the crocodilians ran much cooler at, on average, 88 degrees.

Being warm-blooded is associated with a more active lifestyle and means the “tyrant lizard” could live in a broad range of environments. The researchers calculated that, at least from a temperature tolerance point of view, T. rex could have roamed over most of the North American continent, from Alaska to Mexico.

“All of these habitats would have been viable from a physiological perspective,” Dr. Wiemann said. “It really reshapes our way of asking questions of habitat preference.”

Stephen Brusatte, a paleontologist at the University of Edinburgh, pointed out in an email that the body temperature reading opens up a whole new set of questions about how this celebrity dinosaur operated.