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Re: bauplan convergence



Ronald I. Orenstein  wrote: 
>Folivory is comparatively rare in birds of any kind (possibly because the
>need to eat large amounts of grass and macerate the remains in some >way
adds a weight constraint that is counter-selective for flying birds); 
>The suite of adaptations a bird would need to become a really
large->bodied full-time grazer would probably require a much greater number
>of evolutionary shifts than would be required of (say) a browsing >ungulate.

Metabolic rate per unit meat decreases as animals get bigger (on the
whole). Small animals tend to target energy-rich foodstuffs as a
consequence. Large animals, on the other hand, have the option of targeting
small amounts of energy-rich food or large amounts of energy-poor food.
Bulk processing of low quality plant material, therefore, becomes
increasingly feasible as an ecological strategy as animals get bigger (all
other things equal). So eating leaves is really a game for big animals, and
big animals, for all their talents, cannot fly. This asymmetry between what
birds and (non-flying) mammals have to give up in order to make a living
eating really rough stuff seems to offer a reasonable null hypothesis for
why there are so many more living and fossil hairy leaf-eaters than
feathery ones.

best to all
Chris