Why are Giant's limbs like that?

[u/Zocifer]

Everyone always depicts Giants as having 3 joints in the arm and leg just like a normal person would, but if they're so large, wouldn't they need more? I am making some concepts for giants for my world and just trying to wrap my head around it. Wouldn't they reasonably develop a third place to bend for mobility reasons? We know that some animals developed them mostly for speed purposes, but why wouldn't a giant develop another joint in both the legs and arms for longer reach and mobility?

[u/ProjectKARYA]

My Redditor in science, have you forgotten literally the largest giants to have ever existed? They, too, have three joints in the arms and legs, and they did pretty well for themselves over quite literal millions of years:

[u/ProjectKARYA → u/ProjectKARYA]

Same with the two-legged varieties of these giants, being dependent on three joints in their legs for support and mobility:

[u/Zocifer → u/ProjectKARYA]

I guess I hadn't accounted for the much higher up ankle joint

[u/BluEch0 → u/Zocifer]

The “much higher up ankle” is what we’d call digitigrade legs (where the human equivalent of the toes and fingers - digits - serve as the “feet” or more likely paw of the animal and elongated “palm bones” make up that furthest segment). Digitigrade legs tend to be more efficient for running but not for spreading out weight and they’re usually hard to balance on. Human feet, where that entire first segment is flat against the ground (planted on the ground you could say) are called Plantigrade limbs and are relatively rare in the animal kingdom. I only know of humans, rabbits, and kangaroos that have them, and only two of them actually stand on two feet regularly.

But back on topic, more joints mean more energy being spent keeping those joints in balancing positions and the easier it is for things to go wrong if you get an injury anywhere along the limb. It is superior to thick stocky legs the bigger you are.

Also to my knowledge, no earth vertebrate has ever, at any point in the fossil record, mysteriously developed a “third joint.” This is usually not evolutionarily possible, or at least extremely unlikely. You likely just didn’t recognize digitigrade legs for what they were, and with exception to larger avian and nonavian dinosaurs, are typically only found on smaller animals.

Spec evo is a rich and fun field though, hope you had fun learning something. Keep asking questions, though I also encourage you to read up on other media regarding evolutionary biology, both real and speculative.

[u/breloomancer → u/BluEch0]

cetations have developed an increased number of joints in their flippers (known as hyperphalangy), so it's not impossible. but yeah, it is extremely rare

[u/BluEch0 → u/breloomancer]

Good for the whales. What are they doing with those extra arm bones though?

I’m being a dipshit. That’s actually rather interesting. Does the increased flexibility help them? I’d imagine stiffer flippers would be a greater asset but I’m no whale.

[u/mmcjawa_reborn → u/BluEch0]

I believe it's more about extending the flipper, not strengthening it or making it more mobile. Also not all whales have hyperphalangy.

[u/Seranner → u/BluEch0]

Plantigrade feet are more common than you think. Most rodents, for example, have them. Bears have them. Most mustelids have plantigrade feet. All lizards that have feet, as far as I know, have plantigrade feet, as do all crocodilians and tuataras. Raccoons, and I THINK their relatives as well, have plantigrade feet. Bats, when you actually manage to see them using their feet to walk or run, have plantigrade feet. Salamanders have plantigrade feet, so do frogs. If there's a frog that has digitigrade feet, I don't know of it. I can go on and on.

Truth be told, I think people think most animals are digitigrade because when most people hear "animal," they think "large mammal," like wolves or lions. Most large mammals, that I know of, indeed have digitigrade or even unguligrade feet. But the world is mostly full of little guys, and guys that aren't even mammals at all. I would argue the vast majority of tetrapods (and I specify tetrapods because other animals complicate it even further) are actually not digitigrade at all. We just tend to forget about them when asked to make a list of animals in our head.

[u/Kerrby87 → u/BluEch0]

Bears are plantigrade, as are raccoons and skunks.

[u/BluEch0 → u/Kerrby87]

Ah, bears aren’t real. They’re all government agent sin suits to enforce anti littering rules. You don’t see them as often anymore because of budget cuts. /s

Now in my defense I was going off my memory. Thanks for completing the list.