Lizardmen, gigantothermy, and the energy demand of resting muscles. Could it work out?

Question

One common trope, associated with lizardfolk from Castlevania to Overlord, is their weakness to cold. Now, while it is a fun gimmick, it leaves the problem that lizardmen in Overlord are shown to be intelligent and active, which eats energy and that is a headache for ectotherms.

This is where the dreaded square-cube law comes in. Monitor lizards such as komodo dragons and Asian water monitors exhibit intelligence and emotions while also being fairly active. In terms of size, however, the largest known wild specimen was 166 kilograms (with undigested food still inside) and three meters long. Hafþór Júlíus Björnsson is 180-200 kg AND 206 cm in height.

Now, the square-cube law says that as you scale an object to twice its height, its surface area will increase 4-fold and volume 8-fold. That's important because the surface-to-volume ratio determines how fast something can heat up or cool down, and large animals have much more volume than surface, through which heat escapes. Lizardmen like Zaryusu Shasha are comparable to the aforementioned strongman in size, and I intended on having similarly designed lizardfolk.

This could lead to interesting scenarios as lizardfolk would still be vulnerable to prolonged drops in temperature, so Hot-chocolate Man (OC, donut steel4) is still ideal support for them; and larger lizardfolk would be more resilient, while hatchlings and females would be at greater risk.

On an unrelated note: Why would a female lizardfolk have eyelashes? I guess it's explainable with genetic tampering but still weird.

However, this gigantothermy does come at the price that lizardmen must have a lot of volume, which is mostly energy-hungry muscle. Furthermore, I'm not sure if my trick can completely offset the energy demand of a human-like brain. But then again, crocodiles are a thing, and they are well-endowed with fast-glycolytic muscles that let them tail-slap and death-roll you into Hell where you belong.

So, would gigantothermy be able to solve the actually cold-blooded (ectothermic) lizardmen problem, or the muscles needed would consume too much energy (yes, I could add blubbers, but that feels like a bad idea and not as aesthetic, not to mention buoyancy issues)?

Both images are from E621
Links:
https://e621.net/posts/1635192?q=kazashino
https://e621.net/posts/2295790?q=crusch_lulu+rating%3Asafe

Please try not to click any of the tags. If you do, you'll die. Kazashino is an SFW artist, and a good one, so you may check them out.

Answer 1

the dreaded square-cube law

I'll take that as a compliment.

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When I have to consider human sized reptiles and their metabolism, I like to think of theropod dinosaurs. Deinonychus was about the size of a human adult; while it could reach up to 3 meters (~9ft) in length, over half of that was just its tail; And its weight estimate for an adult lies close to the 70-100 kg (~140-200 lb).

Dinosaur metabolism is a hot topic among paleontologists. [Mental note to self: insert an image quote of Dr. Ross Geller here]. It is practically consensus that theropods were not cold-blooded.

Now, large dinosaurs might have been homeothermic due to their size alone. But according to the wiki, a dinosaur would have to be at least 700 kg heavy (over 1,400 lb) for that to work. Yet so many of them were lighter than that even as adults and had avian characteristics and anatomy. They should have been either tachymetabolic (i.e.: having a high metabolic rate even at rest, such as birds and mammals) or, as the wiki says:

[as a possibility] They were neither cold-blooded nor warm-blooded in modern terms, but had metabolisms that were different from and in some ways intermediate between those of modern cold-blooded and warm-blooded animals.

This makes a lot of sense; some theropods specifically ard the long chain of links between cold-blooded reptiles and warm-blooded birds. If you read the while wiki, there is a lot of evidence that dinos were of intermediate matabolism, but generally more on the warm-blooded side of the spectra.

Your lizardfolk may have the metabolism of dinosaurs, and in this case they can deal with low temperatures mostly like a human of the same size. They just need a bit more clothing when it's cold, like most people born south of Canada or Russia. But in exchange their caloric needs are also slightly below that of a human the same size.

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Why would a female lizardfolk have eyelashes? I guess it's explainable with genetic tampering but still weird.

According to Wikipedia:

Eyelashes protect the eye from debris, dust and small particles and perform some of the same functions as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as a bug) is near the eye (which then closes reflexively).

These have an actual function, so you can blame it on convergent evolution - specially if your lizardfolk don't have nictitating membranes.