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So, as the title suggests, I have a reptilian alien species capable of human-tier thought. Anatomically, they are centaur-like (four legs on the ground, two manipulating limbs up top), standing slightly taller than humans and having roughly twice the body mass. I imagine that these creatures would need a good amount of energy to maintain human-level intelligence and support a human-like society, so they are omnivores; their lower body is of a canine build, letting them run fast enough to hunt large prey animals in packs. I presume that all this energy expenditure can only be supported by a warm-blooded metabolism, but this is where I ask my first question: am I wrong in this assumption? Is it feasible for a cold-blooded sapient species to exist? If you think it is, please shoot me your ideas, because I'm very curious.

My second question is less about sapience than it is about thermodynamics. Can a warm-blooded creature reasonably evolve without requiring feathers or fur to maintain its body temperature? I don't think it's a coincidence that mammals and birds, the two living classes of vertebrates that are warm-blooded, are also the ones with a coat that can either insulate or ventilate as appropriate.

My (warm-blooded?) sapient species is scaly. No coat. Right now I'm imagining that their scales either (1) are very thick/insulating on their own or (2) tessellate together in a way that traps a layer of tiny air pockets. Since this scale layer can't vent itself in case of overheating the way fur or feathers can, they have a "mane" of fleshy tentacles on their heads that are completely scale-free and act as heat sinks. If any of these mechanisms are insufficient, lacking, over the top, or otherwise incorrect--for example, should the heat sink tentacles sweat?--I would love to hear your suggestions for improving them!

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It depends on their environment.

If you think about it, a "cold-blooded" animal (which is properly called an ecotherm) has more energy available for brain power than an endotherm in some cases. They're not using energy to heat themselves, instead they get their heat from their environment.

If the animal lives in an environment that has a fairly stable temperature (in a range conducive to its metabolic processes) then it doesn't need to waste energy heating itself and can more easily spend it on brain power (among other things). Living underground or underwater are excellent examples of stable temperature environments.

Is it feasible for a cold-blooded sapient species to exist?

Absolutely, given a stable environment, it might even be more likely.

Can a warm-blooded creature reasonably evolve without requiring feathers or fur to maintain its body temperature?

Absolutely. If they live in an environment that is close enough to their target body temperature or they make use of tools or environmental factors (like covering themselves in insulating mud) then they don't need fur or feathers to maintain that temperature.

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    $\begingroup$ For real-life examples of naked warm-blooded species: Elephant, Hippo, and Naked mole-rat all qualify! $\endgroup$ – Layna Mar 1 '16 at 7:35
  • $\begingroup$ We are fairly certain there were endothermic crocodilians which supports the second concept, even if the first is hogwash. $\endgroup$ – John Dec 11 '20 at 6:39
  • $\begingroup$ @John You're saying that ectothermic sapient creatures could not exist (the idea is 'hogwash')? $\endgroup$ – Samuel Dec 17 '20 at 20:07
  • $\begingroup$ @Samuel no, that ectotherms have more energy available for brain power is false, endotherms acquire orders of magnitude more energy thanks to a high rate of activity, which is the benefit of having a constant high body temprature. Brains are enormously expensive and require constant energy input, an ectotherm would literally be putting the majority of its energy intake into maintain its brain. endotherms get away with it by having a much higher energy budget. a human brain consumes 800-1000 Kcal per day while a crocodile of the same mass may only eat 2000 kcal in a week. $\endgroup$ – John Dec 18 '20 at 3:20
  • $\begingroup$ @John Endotherms in the real world acquire more energy because they need it. The obvious assumption here is that an ectotherm consuming the same amount of energy would have more to devote to powering a brain. Another way of saying that is exactly what you said, an ectotherm would be able to supply the majority of its energy into maintaining its brain. Which again is what is in my original answer, the ectotherm would have more energy (in some cases, the majority) to spare for its brain. $\endgroup$ – Samuel Dec 19 '20 at 4:19
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Interestingly enough, the octopus is listed as one of the top ten when it comes to intelligence in the animal kingdom, so I don't think it is unreasonable to assume a reptile might achieve sapience. If you are using earthly critters as models it would be a lot more difficult, as mammals have a number of advantages that let them win out over other species, but you could either give these particular reptiles a competitive advantage (poisonous secretions that take them off the dinner menu, or maybe a geographic isolation that removes mammals as competitors)

As to your second question, elephants don't have feathers or fur. Nor do dolphins or whales. All of these are warm blooded and quite intelligent. There is also a species of warm-bloods which have scales, the pangolin.

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