Definitely warm-blooded. And even then, considering their lack of insulation, and the fact that they had been accustomed to warmer temperatures for their whole lives, I think it would be unlikely in real life that they could have survived the conditions depicted in LBT VII (not without frostbite, for sure). If cold-blooded, most of them wouldn’t stand a chance.
Very few scientists nowadays would argue that dinosaurs were “cold-blooded” in the manner of most modern reptiles and amphibians. Though the matter is still debated, it’s generally accepted that dinosaurs were at least partially warm-blooded, as they exhibited several adaptations that suggest warm-bloodedness:
- Many dinosaursóseveral theropods and a few ornithischians like Tianyulongóhad hair-or-feather-like body integument, which likely served a similar insulating function to the body coverings of warm-blooded animals.
- The growth rings and vascular canals in dinosaur bones suggest that many of them grew very rapidly, and had relatively high metabolisms for at least part of their lives.
- Theropods and sauropodomorphs possessed air-filled sacs and cavities throughout their bodies, which probably increased their respiratory efficiency in much the same way as birds (which have similar systems). This would have enabled a higher metabolic rate.
- There are many dinosaurs that lived in parts of the world where, even in their time, the winter would have been too cold for them if they were cold-blooded. While the larger species could have migrated, this would not have been feasible unless they were warm-blooded.
- Dinosaurs almost certainly had four-chambered hearts like birds and mammals. Crocodilians also have four-chambered hearts, but it has been suggested that they are in fact secondarily cold-blooded, and that their ancestorsówhich were small, long-limbed creatures vaguely similar to early dinosaursówere “warm-blooded”.
However, there are a few problems with some dinosaurs being completely “warm-blooded” in the manner of mammals and birds. It has been argued that large dinosaurs like sauropods (longnecks) could not have had such high metabolic rates, as they would have overheated in the warm Mesozoic climate. And there are some dinosaurs whose growth rates seem to have been closer to those of modern reptiles. So not all dinosaurs may have been “warm-blooded” in the mammalian or avian sense. But then, it should be noted that the terms “warm-blooded” and “cold-blooded” are something of an oversimplication of thermoregulatory options. There are a number of other terms to be aware of to understand animal metabolism:
Endothermic: Generates most of the heat needed for energy internally.
Ectothermic: Gets most of the heat needed for energy from its environment.
Homeothermic: Has a self-regulated body temperature that remains relatively constant regardless of changes in the surrounding temperature.
Poikilothermic: Body temperature fluctuates with the remains relatively constant regardless of changes in the surrounding temperature.
Tachymetabolic: Has a high resting metabolism, requiring large quantities of food and oxygen to maintain.
Bradymetabolic: Has a low resting metabolism, with lower food and oxygen requirements.
The classic example of a “warm-blooded” animal is endothermic, homeothermic, and tachymetabolic, while the classic “cold-blooded” animal is ectothermic, poikilothermic, and bradymetabolic. But not all animals fall so neatly into these two categories. For instance, animals that hibernate or otherwise lower their metabolisms to conserve energy become poikilothermic when doing so, even though they are homeothermic. Conversely, bees can generate heat by vibrating their wing muscles (Japanese honeybees are actually known to kill marauding hornets by swarming over them and collectively raising the temperature to a level fatal to the hornet!), though they are technically “cold-blooded”. Some “cold-blooded” animals, such as sharks and swordfish, can even raise the temperature of certain parts of the body, such as the eyes, brain, and swimming muscles, enabling quick reflexes while hunting. All of these creatures are considered heterothermic, as they can alternate between homeothermy and poikilothermy (or, in the case of the last example, effectively both at the same time).
There are also animals that are gigantothermic: while technically “cold-blooded”, their body size allows them to hold onto what internal heat they do generate (for instance, the leatherback sea turtle produces heat through muscular action as it swims; this heat is retained due to its large mass and insulating blubber).
It’s possible that some dinosaurs were intermediate between “warm-bloodedness” and “cold-bloodedness”. Some may even have changed from one to the other as they aged: when young, they had high metabolic rates and were “warm-blooded”, and as adults their metabolisms slowed down and they became more “cold-blooded”, maintaining their body temperature through their immense size. Others may have had a metabolism that was higher than that of a classically “cold-blooded” animal, but not as high as a mammal’s or bird’s. And some (particularly the small, birdlike kinds) could have been truly “warm-blooded” their entire lives. Considering the diversity among dinosaurs, it wouldn’t surprise me if this were the case.
