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To clarify some points concerning the link between limb posture and

The link applies only to animals that spend the majority of their time walking
on dry ground. 

Energy cost of locomotion is pretty much the same regardless of limb posture
and design, it is primarily a function of size. 

For most animals, energy cost of locomotion is pretty much a simple multiple
of speed (humans and elephants are unusual in having a U-curve relationship). 

A few lizards do keep standing and walking many hours at a stretch. 

Only animals with high aerobic scope (these days birds and mammals) can
sustain walking speeds over 1-2km/h. This is true regardless of limb form or
body mass. No reptile has been shown to do so (even the most aerobically
capable monitors). The teiid lizards that stand and walk for many hours move
at only a fraction a kilometer per hour. 

Sprawling limbs are good for slow walking (below 2 km/h), because the provide
a stable platform that will not allow the animal to tip over as it walks
slowly. Sprawling legs are also suitable for high speeds. 

Long erect legs work under a strong pendulum effect. They are therefore ill
suited for slow walking, and tend to force walking speeds to be above 3 km/h.
You can try this ourself, walking slowly is not quite comfortable, we "feel
better" walking at 5 km/h. Because walking so fast is "dynamic" in that
tipping over is prevented by rapid foot placement, a narrow trackway is

A sample of many hundreds of erect legged animals, including a few hundred
dinosaurs, found that 95+% walked at speeds a
of 2-3+ km/h. 

Because long erect legs probably force land walking speeds to exceed 2 km/h,
and reptilian aerobiosis cannot sustain such high speeds, the evolution of
erect legs probably forces aerobic scopes to be elevated above the reptilian

Because dinosaurs had long erect legs, and because trackways show that they
almost always walked faster than 3km/h, they should have had an aerobic
capacity above that observed in reptiles. 

Chameleons have erect legs. They evolved in order to allow stalking at
extremely slow speeds along narrow branches. Because normal speed is slow
rather than fast, the erect legs do not force an elevation in aerobic