Is it possible for a human or human-sized animal to be an ectotherm?

Question

When I say human, I don't mean an actual human. I mean, like, a humanoid creature.

Also, if they were ectothermic, what would this do for their habits? Would they not be able to move around properly unless they warmed up?

Or would they be able to absorb and stay homeothermic part of the time like when sea turtles absorb and hold heat (due to their size) on the surface before submerging?

I am confuuused.

Answer 1

Ectotherms (also known as poikilotherms from the Greek poikilos meaning variable and therm meaning temperature) obtain heat from their environment.

It is quite possible to have large ectotherms.  Today we have things like komodo dragons.  Historically, the largest creatures ever to inhabit the planet were ectotherms: the dinosaurs.

They cannot function unless their temperature (which generally matches that of their environment) is sufficiently high for biochemical precesses to occur.  The nearer to 37 C, the better.  That is why alligators live in Florida rather than Alaska and big snakes tend to inhabit warmer climates.

All reptiles, fish and amphibians as well as all invertebrates are ectotherms and there is nothing they can do to change this.  The only endotherms are birds and mammals.

Answer 2

No. Any humanoid creatures will be mammals. Any ectotherm will look more like a crocodile or shark.

Answer 3

Although I've met a number of reptilian men I don't believe they were truly ectothermic.  Since humanoids are mammals, they're not going to be ectotherms, they are homeotherms.  There are large ectotherms:  crocodilians, most sharks, large constrictor snakes.  A turtle is an ectotherm too, not a part-time homeotherm.  Homeothermic refers to warm blooded and you are or you aren't.  Ectothermic refers to coldblooded.  There's no halfway on this.  

Answer 4

Sure, why not?  You've got giant tortoises, anacondas, komodo dragons.

Oh, by the way, the dinosauria were (and are) warm-blooded.  Read the book "The Dinosaur Heresies" for several pieces of evidence supporting warm-bloodedness.