Re: erect crocodile problems

["Tony Canning" <tonyc@foe.co.uk>]

On Jun 8,  3:13pm, Colette H. Adams wrote:
> Subject: erect crocodile problems
> The man asked to be convinced, so here goes.
>
> When a physiologist measures the resting metabolic rate of a crocodile,
> (s)he does not make it stand up to do so.  Standing up is not considered a
> resting position for a reptile.  A crocodile on its feet consumes
> considerably more energy than a resting crocodile.

Has this been measured then? I would very much like to see this data if
you have a reference.

>
> The only reason a terrestrial vertebrate can take advantage of the energy
> efficiency of ectothermy is because it can flop down on its belly most of
> the time.  Greg Paul has said previously on this mailing list that a fully
> erect posture probably forces elevated aerobic exercise capacity.  I would
> take out the probably.

Again, the only data I've seen put the difference between erect posture
and lying down (biped) at about 4% increase O2 consumption (I think).

> Yet in the final analysis, it does not matter how many hours a day you
> spend on your feet.  Big cats lay around most of their lives, yet have
> never evolved ectothermy. This is because a fully erect posture forces a
> walking speed beyond that which can be sustained by ectothermy.  Abundant
> trackway evidence tells us that dinosaurs routinely walked at speeds of
> 5-10 kph.  Yet a green iguana will become exhausted within 17 min at a
> speed of <0.5 kph.
>

I think comparisons with green iguanas reveal little - they are tree-
climbing specialists, not walking specialists.. Also, logically, from
A (mammal physiology) not equal to B (iguana physiology), and C (dino
phys) not equal to B, you can't conclude C=A.


> Selection for energy efficiency might indeed be expected to push towards
> ectothermy.  The problem is that endothermy is such a huge physiological,
> molecular, and morphological commitment  that it is very difficult to
> reverse.

Are not crocodiles descended from bipedal ancestors? If so, they were
either ectothermic bipeds or endotherms with ectotherm descendents?

Best wishes
Tony

Tony Canning
tonyc@foe.co.uk