Analysis of the chemistry of dinosaur egg shells can reveal if the dinosaur was warm blooded (i.e. in a broad definition of "warm blooded" they had an internal body temperature consistently and significantly above that of the environment) or cold blooded.
Evolutionarily, dinosaurs are between reptiles (which are generally cold blooded) and birds (which are generally warm blooded), so there is no strong reason to favor one hypothesis over the other, particularly now that we known that many dinosaurs has something like feathers. The closest widely familiar bird, evolutionarily to the dinosaurs, is the chicken.
All dinosaur eggshells analyzed to date support the hypothesis that the dinosaurs involved were warm blooded, although some had more of a differential with respect to the environment than others.
The different dinosaurs varied in how much their body temperatures were higher than their environment. The Troodon samples were as much as 10 C warmer, while the Maiasaura were 15 C warmer. The Megaloolithus samples showed the smallest range of 3 C to 6 C warmer.
"What we found indicates that the ability to metabolically raise their temperatures above the environment was an early, evolved trait for dinosaurs," Dawson, the lead author of the study that published last week in the journal Science Advances, said in a news release.
Whether dinosaurs were cold or warm-blooded has been a long-running debate among paleontologists. A study from 2014 suggested they were neither, occupying a middle ground.Via CNN.
The 2014 study isn't necessarily inconsistent with this one, because it recognized the possibility of a middle ground between warm blooded and cold blooded, which the current study doesn't appear to (and may not have a way to distinguish).