The growth lines they found on the ruminants were similar to those seen in previous studies of dinosaur bones — indicating that both ruminants and dinosaurs have periods of high growth punctuated by "unfavorable" seasons with limited resources and little growth. This means that dinosaurs were likely warm-blooded like the ruminants.
"The argument we are giving in our paper, rather in favor of endothermy in dinosaurs, is that between the growth and rest lines, there's always a big region of highly vascularized [infiltrated with blood vessels] tissue that indicates very high growth rates," study researcher Meike Köhler, of the Autonomous University of Barcelona in Spain, told LiveScience. "This is typical in dinosaurs and very different from reptiles, which have slow growth between the rest lines."
Sauropods were the only dinosaurs where researchers haven't seen growth lines similar to those of ruminants. Previous studies of their teeth indicate they would have had high body temperatures as well, though they might have been big enough for their mass to generate that heat — what researchers call a "gigantotherm." Researchers don't know what their growth lines would have looked like, since no animals alive today are gigantotherms.
This indicates that "dinosaursalso had very fast growth rates and needed to eat a lot and maintain high generation of heat internally," Kohler said, so they were most likely warm-blooded.