Re: ornithomimes and herbivory

[Ronald Orenstein <ornstn@inforamp.net>]

Nicholas Longrich writes:

>       Diatryma doesn't really look like a big herbivorous bird. The 
>problem is that skull- it's enormous, especially compared to herbivores 
>like moas, elephant birds and the other ratites- which, if I recall, 
>mainly eat plants, though some will take animal matter as well.
>   Herbivorous birds generally don't have big beaks probably because they 
>mainly serve to take in food, rather than to process it.

Actually, this generalization is not true.  Toucans and hornbills are partly
frugivorous at least, for example.  The beak is not just for taking in food,
but can process it by, say, cracking seeds; consider the large, powerful
bills of the bigger parrots (a Palm Cockatoo or a Hyacinth Macaw, for
example), or the bills of some of the Galapagos finches and other seedeaters
(some of which are not, after all, called "grosbeaks" for nothing.  Large
bills can also be used to get at plant food (consider the rather heavy bills
of some partidge-like birds such as snowcocks).

The closest thing to a Diatryma today, ecologically speaking, might well be
something like the Takahe Porphyrio mantelli of New Zealand, which is a
large flightless herbivore with a very large bill compared to its nearest
relatives. In fact the closest thing to a Takahe is the widespread Purple
Swamphen Porphyrio porphyrio, which has a smaller bill and is partly
carnivorous - so in this case a switch to a purely herbivorous diet has been
accompanied by an increase in bill size.  To quote Raymond Harris Ching in
"New Zealand Birds":

"...they feed on seeds and other plant material, in particular the soft
bases of snowgrass, Danthonia flavescens.  To secure these stalks, the birds
may flatten off a largish area of a clump of Danthonia and hack away at it
with their massive beaks.  In this manner, pieces are cut loose to be held
tightly and precisely in the bird's toes..."

I certainly have no trouble imagining Diatryma using its bill to dislodge
vegetation in a similar way.

--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
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