Cold or Warm blooded?
There is a considerable debate amongst scientists and Dino lovers alike as to whether Dinosaurs, as well as flying and swimming reptiles, were cold blooded or warm blooded. If they were/are cold blooded or Ectothermic, the animals would rely on their environment to sustain adequate body temperatures. If they were, on the other hand, Warm blooded or Endothermic, the creatures would be able to sustain body temperatures largely on their own.
The theory of warm blooded Dinosaurs and kin arises from the idea that many species of these ancient reptiles were not sluggish, slow and dim witted as they were long thought and depicted. During the 1970's the "Dinosaur Renassaince" was a period when many researchers went through and reexamined these fossils and found that many were actually fast, swift and intelligent, and that they may have to have been warm blooded to sustain the more active lifestyles.
This theory was later made even more popular due to supposed feathered Dinosaur fossils, since birds are warm blooded, it would logically follow that if Dinosaurs had feathers they would have to have been warm blooded, meaning they regulated their own body temperature such as mammals and birds and unlike reptiles.
The problem with Dinosaurs being warmblooded is that the evidence for it is underwhelming or missing altogether. Warm blooded animals and cold blooded animals have some key differences in their features. Such as, if Dinosaurs were warm blooded and lived the lifestyles they supposedly did, they would have had either hair or feathers, and even though there have been numerous "feathered Dinosaur" fossils found, they have all been shown to be either hoaxes, normal Theropod dinosaurs or 100% birds. None have been shown to be authentic fossils of Dinosaurs with feathers or hair.
Some have said birds evolved from Theropod dinosaurs, and some have even said that Dinosaurs were mammals, these allegations are based on underwhelming scientific support at best. Currently, the vast majority of evidence points to Dinosaurs and their kin being 100% reptile, albeit very unique reptiles, but fully reptile nonetheless.
One of the conflicting issues with Dinosaurs being warm blooded is that aside from little to no evidence supporting it, there is no biological need for even the fastest and most active Dinosaurs, ie. Velociraptor, to have been Endothermic. There are plenty of cold blooded animals, including reptiles, alive today that are cold blooded yet still move very fast, much faster than humans. There are many lizards and crocodilians, the closest animals in function and appearance to Theropods, that can outrun a human and many other potential predators. The fastest lizard alive today is the Spiny Tailed Iguana has been clocked at 21 miles per hour, much faster than any human can run, yet they are still cold blooded animals.
It only seems reasonable that Theropod Dinosaurs would have been had similarly active lifestyles, being able to achieve high running speeds without needing abnormally high amounts of food to sustain their metabolism. They could have simply ran only when they needed to and rested when not hunting, and it is also likely that they prefered to hunt smaller prey which would be easier to catch and would require less energy.
There is also a third, interesting possibility. Dinosaurs, Pterosaurs, and Plesiosaurs may have been reptiles that posessed both ectothermic and endothermic traits. Many animals today that are ectothermic can tolerate very low temperatures such as fish and a number of species of reptiles and amphibians. Different animals are adapted to different climates and habitats, and obviously the dragons of old would have been no different in their need for proper adaptations and needs. This may in fact be an explanation as to why some alleged "Lake Monster" sightings occur in such cold waters as Loch Ness in Scottland despite the animal being reptilian.
There seems little reason to think any Dinosaurs, even Theropods, were warm blooded mammalian or avian creatures. There simply is no scientific evidence to support anything but being reptiles like modern day lizards and crocodilians.
Such amazing animals were certainly wonderfully made and we can see that from just what little remains we ahve to work with. We must be careful of making scientific dogma out of specualtion based on the bones of dead animals. Remember that no one would know elephants had trunks if they just exmained elephant skulls.