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Lecture 1:

Listen to part of the lecture in a biology class.

Until about 30 years ago, scientific opinion was pretty much unanimous in thinking that dinosaurs were cold-blooded creatures, and not warm blooded like mammals and birds.What are these terms cold- and warm-blooded mean?

Well, they are imprecise terms, a little bit inaccurate, but for the sake of consistency, I’ll continue to use them.

Warm-blooded animals, or technically, endothermic animals, are animals that use their own metabolism to maintain a relatively high, generally constant body temperature. They generate their own heat, whereas cold-blooded animals, uh, technically called ectothermic animals, cold-blooded animals rely on the environment primarily to regulate their body temperature. And their body temperature can actually vary a great deal depending on the temperature surrounding them.

Now, as I said, mammals and birds are warm-blooded creatures, and we being mammals, you’re familiar with, you know, your body stays pretty much the same temperature all the time, whereas if you’ve ever seen, say, snakes or lizards you know, basking in the sun on the rock, you can see the characteristic feature of a cold-blooded creature that is using the environment to help regulate its body temperature.

As I said, until about 30 years ago, dinosaurs were, because they seem to most closely resemble reptiles, they were thought to be cold-blooded. Then about 30 years ago a number of scientists began to suggest the possibility that dinosaurs might in fact be warm-blooded. This was very exciting for a variety of reasons.

Warm-blooded creatures are closer to us. They are more active. They move faster.

They can live in a wider range of environments than cold-blooded creatures. So a lot of scientists kind of got on this bandwagon for warm-blooded dinosaurs. But unfortunately, a lot of the evidence for dinosaurs possibly being warm-blooded is indirect.Among the pieces of evidence is that the fossilized remains of dinosaurs have shown that certain kinds of dinosaurs had feathers.

Now, feathers in birds, one of their main functions, apart from helping certain birds to fly, is that they are an insulator. They preserve body heat, so by analogy, some people have argued, well, ok, if they were feathered dinosaurs, maybe they had feathers for insulation. Yes, maybe. But maybe not.

Another piece of indirect evidence is that some dinosaurs, uh, well, some dinosaur remains have been found in areas, latitudes that today have arctic climates and might in fact had very cold climates at the time that the dinosaurs were living there. It’s hard to function as a cold-blooded creature in an arctic climate.

Unfortunately, we don’t have exact climate information. It’s only been suggested that these areas might have been as cold as they are today. So again, this is not, you know, not a knockdown argument in favor of dinosaurs being warm-blooded.

Another argument for the warm-blooded theory has to do with looking at the anatomy of dinosaurs and at the similarities with warm-blooded animals. If you look at what’s around today, well, let’s see, today anything that walks on two legs is warm-blooded. That goes for humans and some other primates,and birds like the ostrich, okay? Only warm-blooded creatures, you know, like ostriches, have upright posture.

Alright, so proponents of the idea that dinosaurs were warm-blooded say, well, look at dinosaurs, some of them had upright posture too. Coincidence? They say no, these two-legged dinosaurs were warm-blooded too. Okay, but on the other hand, as far as we can tell, dinosaurs lacked a body structure called the respiratory turbinate. Why is that significant?

Respiratory turbinates are these complicated structures inside the nasal cavity.

They are aligned with soft tissue and their function is that as the air passes through these complicated kinds of curlicue passages, air coming in is warmed up, so that warm-blooded creature isn’t shocked by it. Its lungs aren’t shocked by receiving cold air directly from the outside, which would really disturb its internal temperature. So unless there are some other mechanism that we don’t know about, it seems that these, that dinosaurs lacked this vital feature of all existing warmblooded animals.

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