Thioethers preserved in bones show that most dinosaurs were warm-blooded, though T rex may have been particularly sluggish
Analysing oxidative stress compounds in fossilised bones revealed that most dinosaurs, including giant sauropods and theropods like Tyrannosaurus rex, were warm-blooded like modern birds. But Stegosaurus, Triceratops and hadrosaurs likely reverted to reptile-like cold-bloodedness.
All extinct dinosaurs were once thought of as reptile-like ectotherms, animals that operate on low metabolic rates and require environmental heat sources to increase their body temperature. Since the late 1960’s, scientists have started to find evidence that dinosaurs were active, warm-blooded animals (endotherms) more akin to birds and mammals. But whether all dinosaurs were true endotherms is still debated.