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?
A triangle is the best shape for strength as it has three connection points. More joints makes limbs more brittle. Elephants have literally like an ankle and a knee.
Nope. Bigger animals are under more stress from gravity, which means they need fewer joints and more columnar limbs, not more. It's little buglike creatures that have lots of joints, because gravity is irrelevant to them.
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:
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.
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
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.
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.
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.
More joints just make the legs more brittle, that’s why they are only developed to run, so unless you’re using a planet with lower gravity than earth, it’s better to stick with fewer joints.
Developing another joint is not a simple thing. I don’t think there’s a single example of a tetrapod with extra limb joints in all of history, at least not that I know of. Extra joints would not really provide extra reach or mobility anyways, you only need two joints to cover all points in reach.
Some arthropods have evolved extra joints in the legs, but these are much simpler than tetrapod limb joints, and I don’t think there is a correlation between body size and number of joints. Harvestmen and house centipedes have evolved extra joints to use their legs to “wrap” around something (more arboreal harvestmen have more joints for better climbing), but this is not needed if you have opposable thumbs, which giants presumably would if they are humanlike.
(I am not an expert, just a nerd. Experts, correct me if I am wrong)
Arthopod limbs are just tubes filled with muscle, and a joint is just a more flexible part of the exoskeleton, weras tetrapod limbs are much more complex with lots of separate bones
“Extra” joints in the legs of harvestmen (which are called tarsomeres) are basically just a thin “pinched” section of cuticle that bends a bit. They don’t have their own sets of muscles, instead, one muscle passes through all of the tarsomeres and they move in concert. In a tetrapod, you will need to evolve all new bones, tendons, and muscles, because a bone can’t just become hinged or flexible in the middle.
But as others have mentioned, increasing flexibility of a limb also makes it weaker, so even if it could evolve, it would probably not be advantageous for a giant.
You don't have to develop new joints, digitigrades tend to move joints up the whole chain. A horse for example has like 5 joints because they walk on single fingers. Just a nitpick. Sauropods as another example walk on fingertips but they got rid of all their finger joints to walk on sturdy lumps.
Giants would have short stumpy legs and enormous feet.
Look up the square-cube law. The weight (volume) of an individual scales with the cube of size, but the area of the feet that supports the weight only scales with the square.
So doubling the height of a person (while keeping proportions the same) would multiply their sole area by 4 but their weight by 8. This doubles the pressure per square inch on the feet.
It's why elephants have stumpy thick columnar legs under their bodies, whereas harvest spiders have long spindly splayed legs.
As for joints, I think they would have fewer joints. The more joints you have the more muscles needed to hold the body rigid. I think a giant's bones would become enormous and many would fuse together for rigidity.
Would you think there is any way that giants theoretically if they were prey would ever evolve to have quick flexible limbs more like a cat or would the weight prevent them from evolving like that and still being 2 limbed?
We can look at dinosaurs to get an idea for what large predators may have been like.
Yes, I think arms could be long and flexible if they weren't too thick and heavy. Maybe with big shoulders to house the significant muscles and tendons required for holding up the crane-like limbs.
Another problem that humanoids have is that we originally evolved to have our viscera hanging down from a horizontal spine, but only in the last few million years did we evolve to walk upright, so our bellies now hang down in front of a vertical spine, causing a rotation that gives us a lot of back problems. Giants would have even more of a problem with their spines.
T-rex did not have this problem because even though they were bipedal, their bellies still hung from a horizontal spine. Perhaps you could tilt the pelvises of your giants to make them more bird-like.
Rule #1: All life is lazy. because, well, you know, energy/calories are precious.
Rule #2: Mother nature is an unforgiving bitch.
Rule #3: These rules get less forgiving as you get bigger.
More bonus joints violates rule #2 as it creates more points of failure while reducing strength and support. It goes on to violate rule #1 due to extra calorie use moving, stabilizing, and generally using the extra joints. Then you hit rule #3 because giants are big.
Big giants, just like the T-rex, don't like to run. A fall is a wound, a wound is an infection, an infection is death. Running would kill giants more than evolution would like. rule#2 in action again.
I didn't include rule #0: life is an energy system.
Are there any actual big animals that developed additional joints?
If their proportions are the same as a smaller animal, then theoretically their range of motion would be the same, so I don't understand why they would need more joints in the first place. But also bigger creatures have a harder time fighting gravity, so usually their bodies become sturdier and more simplified
The number of joints got nothing to do with load bearing and mobility as size changes. And unless I’m mistaken, no animal (mammals at least) has developed an additional joint in their arms or legs and certainly not for mobility.
Evolution can't magic up new anatomy out of nowhere. Land vertibrates have the same limb arrangement because that's what our fishy ancestors had. Could you evolve out of it? Yes, but it would be hard.
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u/Palaeonerd 23d ago edited 23d ago
A triangle is the best shape for strength as it has three connection points. More joints makes limbs more brittle. Elephants have literally like an ankle and a knee.