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May 2016

The Bellinghman
Date: 2009-06-26 10:50
Subject: Did bipedalism evolve from high acceleration?
Security: Public
Avoiding 'wheelies' slows animals: The acceleration of four-legged animals appears to be limited by their need to avoid tipping upward, thus losing traction as their legs miss the ground.

This is interesting. The first creatures we know of that had high 'warm-blooded' metabolisms were the dinosaurs. And the dinosaurs were the first group of creatures that started using bipedalism. (Not all, of course, not the slow browsers.) Perhaps they became two-legged because once you have so much muscle power that you start rearing up when you try to rush, you might as well go with it and put all the power into the legs that stay on the ground.

It'd also explain why cheetahs have non-retracting claws: those claws aren't primarily for attack, they're for extra grip.

(If I recall correctly, a good sprinter can beat a racehorse off the line - just not over the first furlong.)
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Jos Dingjan
User: happydisciple
Date: 2009-06-26 10:37 (UTC)
Subject: (no subject)
Trouble is, if you go bipedal you still have to adopt a close-to-quadrupedal stance for maximum acceleration, and you'll have serious problems decelerating.

I was glad to see Eq. 1.1 in that Biol. Lett. (which is freely accessible, btw), as I'd just derived the same using a bit of scrap paper and 2 seconds.
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The Bellinghman
User: bellinghman
Date: 2009-06-26 11:02 (UTC)
Subject: (no subject)
Oh, there are trade-offs all over the place. Deceleration for quadrupeds can get interesting though, as they can end up tumbling head over heels, unable to lean back and stick their feet in, the way bipeds can ... oh hold on, quadrupeds are supposed to be better for this?

(I think cheetahs prefer to go for the falling over in a great big heap option, entangled with their prey.)

I note that where the referenced article does discuss high deceleration in quadrupeds, the animal is sitting back on its haunches - again, a bipedal strategy where concentrating all the strength in back legs works better than even distribution.

As for that acceleration, yes, your biped is leaning right forward. That's the advantage of the biped: it can do that.

If I were to design a followup study, I'd want ostriches included. Their top speed is comparable to that of horses, and they're the closest thing we've got to high-speed dinosaur-style bipedalism. (Human style is based on endurance - there are hunters recorded who can chase deer to exhaustion.)
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Erik V. Olson
User: erikvolson
Date: 2009-06-26 14:43 (UTC)
Subject: (no subject)
Yeah -- look at racing cyclists on a sprint -- they're far forward, to keep the front wheel in enough contact with the ground to maintain control.

They're also pulling up, hard, on the handlebars, because their legs are trying to push them -- hard -- off the pedals.

A very solid definition of "serious suck" is what happens when the handlebars fail in a sprint.
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