I first posed the question to my elementary school science teacher circa 1973 whether the dinosaurs weren't in some way usefully self-warming. I didn't have the vocabulary about homeostasis or mesotherms at that age.
So, young man, you're suggesting that the dinosaurs might have been mesotherms?
"Meso", everyone, means "in between" or "intermediate". So the idea here is that dinosaurs would be warmer than modern reptiles but not as warm as modern mammals—whales and cats and dogs and humans and horses—who maintain a fixed body temperature. By "fixed" temperature we mean within a narrow range, subject to regulation, or control. Among the regulatory abilities in humans are sweating when we get too hot, and shivering when we get too cold. (Does anyone know if whales shiver? Someone try to find that out for class tomorrow.) When our body temperature regulation fails we experience fever or chills. Chills are known to doctors as hypothermia, "hypo" meaning reduced and "thermia" meaning temperature; hypothermia means "reduced temperature". Fever and hypothermia are dangerous conditions that require prompt medical attention.
It's different when a lizard gets cold. For the lizard it's not an immediately dangerous condition; it just becomes sluggish until its environment warms up again. Now our lizard might be subject to predation—being eaten by a predator like an eagle or a snake—if it becomes sluggish at the wrong time or in the wrong place.
Mammals are the opposite in both ways: our temperature remains fairly constant regardless of our environment, and when our body temperature—not in our arms and legs and hands and feet, but inside our skull, our chest, or our belly—when this internal temperature changes, that's a big thing to worry about.
A mesotherm would be an intermediate creature, one who is able to generate enough body heat to remain active in a cold environment, which helps to avoid predation (remember that means being eaten), but isn't directly threatened by having a cold body temperature, if the food supply does not support maintaining a high activity level.
Something science has learned is that any organism that goes too long without food ceases to generate warmth internally. Now a large pile of dead plant matter—yard waste—can become much warmer than the surrounding environment, but this is due to smaller organisms with the plant matter which are busy eating the plant matter. It is also true that rotting meat will generate warmth from the small organisms inside the meat causing the meat to rot. Whatever the situation, if heat is being generated in a biological system, somewhere in that system there is some form of digestion taking place.
Now let's go back to the excellent question about dinosaurs could have been mesotherms. As young scientists, you are probably all wondering what is the evidence that dinosaurs were cold blooded or not. That's a very good question, everyone.
As a scientist, I wondered this myself. As a scientist we are trained to ask these questions whenever possible and seek as hard as we can to obtain the answers. Over my summer holidays—can you believe that?—I scoured all the science textbooks available to this school district, and I can't find a single sentence in any book explaining why dinosaurs are believed to be cold blooded, apart from their having a distant kinship with modern reptiles.
But then, think about this yourself. We know modern reptiles are much smaller than dinosaurs, who were waaaaay bigger than elephants. Large creatures often generate more heat than they want to have, which is why elephants have those giant, thin ears. All that extra skin helps them to transfer unwanted heat into their environment.
We'll be talking more about the relationship between heat and temperature in future classes. This is an important concept which is central to life as well as to modern machinery, which is why we eat regular meals and our cars visit gas stations. Heat and temperature are both connected to the concept of energy. That's a very important concept you'll be visiting year after year in your school education.
Unfortunately, it appears that all your textbooks—all the way until you leave school when you are much older—we written by the same idiot, who isn't a proper scientist at all. So we're all going to have to work hard to figure out our own answers to these important questions by thinking carefully in our own minds and challenging each other to support our opinions.
Does that sound like a good idea? Yeah, it does, doesn't it.
Well, my young students, I suspect that would be the principal's office summoning me to the guillotine for my immediate beheading.
I love you all, and I'll miss you so much. Good-bye everyone. It was worth it.