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Re: Dietary factors & giant land mammals - birds



Two older answers...

----- Original Message -----
From: <MarkEShelly@aol.com>
To: <dinosaur@usc.edu>
Sent: Tuesday, May 08, 2001 2:00 PM
Subject: Re: Dietary factors & giant land mammals - birds


> John Bois said <<And yet, to see a bird with the mass of a bison or a
wilderbeest would be impressive enough.  I suppose there are food processing
limitations on this.>>
>   Speeking of food processing limitations. Maybe the reason birds did not
become gigantic was simply because they could not get enough food.
>   How easy is it to peck an animal to death.  Without teeth, especially
replaceable teeth, it would be extremely hard to kill any large animal, or
catch enough small ones to grow extremely big.  I wouldn't be surprised if
the lack of replaceable teeth also limits current land mammal predator size.

A hooked beak seems to be terrible enough, I'd say, regarding e. g.
phorusracids. The biggest known neornithines are among the carnivorous
dromornithids and 3.7 m high. This is not gigantic sensu P&L, but if
gigantic prey and no other large carnivores were available, I don't see a
reason why one couldn't inflate such a bird to over 1 t.

>   For a plant eating bird, the lack of teeth probably prevents chewing
hard plant tissue, at least enough to build a large body.

Sauropods didn't chew either

> While it is possible to have evolved a system to use stomach stones to
help digestion, was it possible to clip enough food with a beak?

Why not, if the beak is sharp and strong enough (as moa beaks apparently
were)?

> The lack of replaceable teeth in mammals may also be a reason they did not
evolve larger.  Elephants appear to be headed towards the dinosaur
condition, but not there yet.

Maybe chewing itself is a limiting factor: It requires big teeth and big
jaws and thus big, heavy heads that need to be carried. Even a giraffe head
is considerably bigger than that of a sauropod with the same neck length.

> If man evolved from bacteria,

We didn't (if we don't agree with HP Ken Kinman, that is, and I don't know
most of his evidence). Eucarya (or -k-?) + Archaea is considered the sister
group to Bacteria.