This might be a really weird question, but why do Kangaroos jump instead of walk?
As a human jumping takes a lot more energy than jumping, so it must be something biological, but they are like the only animal family that does that (I’m sure there are more kangaroo-like animals I don’t know about)?
Edit – After seeing a few comments, this post isn’t about why the evolved to do so (even though it is an interesting question), I was asking what is the anatomical reasoning for it.
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This is literally the crux of both morphology and physiology. I’m not making dunno you, but you could just as easily ask, “Why don’t peille swim by wiggling their body side to side? It works for fish and crocodiles?”
Jumping is SO much easier than walking or jogging, for a kangaroo. So much so that it is l one of the most energy-efficient forms of animal movement t ever to evolve, about tied with humans, who have INSANE levels of efficiency in a walk or slow run, and about double humans, much, much more efficient at high speeds.
To walk like us, though, a kangaroo’s waist is too stiff, it’s pelvis is all wrong both in the angle of the pelvis, the location of the hip sockets, and angle of the hips. It’s limb proportions between the femur, the tib/fib, and tarsal bones is way off, and it’s foot is too stiff (it would have to walk on the tips of it’s claws/nails. They can’t straighten their knee fully, and don’t have proper kneecaps. Just for starters.
To walk on two legs like a dinosaur would be easier, but still not right. Remember kangaroo ancestors probably DID stride with their back legs when they still used their front legs. In that case the absence of some key muscles that run from the base of the tail to legs are missing. Dinosaurs had something called a caudofemoralis muscle, but mammals don’t, so our “glutes” and lower back muscles that support our stride are above the leg, and not on our tails, and are not used the same way. That’s why 4-legged mammals walk, shuffle, trot, bound, etc.. on a dinosaur or a chicken the step and stride is exactly the same, just faster and faster.
So, take an animal like a rabbit, which is an exaggerated bounder and leaper. Even when “walking” a bunny doesn’t go left/right front, right/left back like a cat does. He takes little slow-motion hops, both fronts then both backs.. Speed that up and he’s taking long leaps. Why don’t rabbits bounce on his their hind legs, then? They SOMETIMES do, but the posture Is very upright, because they don’t have a balancing tail, for one, and their plump rumps are way in the back.
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