Were dinosaurs warmblooded? More precisely, were they ectotherms, with low metabolic rates, like living reptiles, or endotherms, with high metabolic rates, like mammals and birds? (Yes, yes, you and I know that birds are dinosaurs, cladistically speaking, but you know what I mean.) And there are other possibilities: were the biggest dinosaurs, the sauropods, gigantotherms, keeping metabolic rates low, but staying warm through sheer size?
Endothermy is a big deal:
Elevated metabolic rates enable animals to remain active year-round at high latitude and altitude. They also enhance physiological performance, improve endurance, increase activity levels and facilitate rapid niche shift during environmental perturbations.
https://www.nature.com/articles/s41586-022-04770-6
Recently, it has become possible to address this question by looking at chemical signals of metabolic rates in fossil bones. The chart below (see link above) summarizes the results.
The upper branch of the tree are the diapsids – reptiles, dinosaurs, birds, and relatives. The lower branch is the synapsids – from dimetrodon way back in the day to mammals today. The chart shows that the earliest dinosaurs had high metabolic rates, as did the closely related early pterosaurs. And the sauropods were true endotherms. But some later dinosaurs actually gave up on endothermy: triceratops, stegosaurus, and the hadrosaurs (duck-billed dinosaurs) seem to be secondary ectotherms. Other dinosaurs went for more intense endothermy, like allosaurs and diplodocus and some close bird relatives.
In short, dinosaurs are diverse.
Logarithmic History 