Xref: utzoo sci.bio:1931 talk.origins:4610
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!sabol
From: sabol@Apple.COM (Bryan Sabol)
Newsgroups: sci.bio,talk.origins
Subject: Re: The birds and the beaks
Keywords: evolution, birds, beaks
Message-ID: <27216@apple.Apple.COM>
Date: 13 Mar 89 19:51:28 GMT
References: <404@censor.UUCP>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 65

In article <404@censor.UUCP> jeff@censor.UUCP (Jeff Hunter) writes:

	>Hello there. I was having a conversation with a friend recently, and
>the question came up "Why do all birds have beaks?". I finally concluded
>that somewhere just after archeopteryx there was an overwhelmingly successful
>bird that ate nuts (or had some other compelling reason to lose teeth and
>get a beak). Subsequent generations of birds got their beaks by inheritence,
>and were able to modify them to different tasks rather than having to 
>re-develop teeth. Alec instead concluded that beaks have some advantage for
>feeding if you've lost your forepaws  ('cause they're wings).

	I must admit that ornithology isn't my specialty, but if I
remember a prof's theory correctly, she thought that the beak was
developed as a means to lessen the bird's overall mass.

	To be able to fly, ancestral birds needed to modify existing
structures to lighten their bodies, yet retain similar function with
these adaptations.  A good example would be their bone structure.  All
(flying) birds have hollow bones, with a lattice-work or gird-like
structure, giving them strength without the much greater mass of
standard solid bones.  

	The beak was a sophisticated modification that enabled birds to
rid themselves of the great amount of weight which is associated with
teeth and their supporting structures.  Though the teeth themselves
aren't what comprise great mass, the supporting structures associated
with teeth *are* massive.  Note, for example, the size of many predators' 
skulls:  the size and weight of the bones which are supporting the teeth
are very large.  To operate teeth, one must also have a strong jaw which
houses the teeth.  Then one needs more thick bones to support the large
muscles needed to operate the jaw:  the development of cranial ridges
was expressly for the operation of these powerful jaws. (Also, these large
cranial ridges are not unique to one type of food source;  they can be 
found in both carniverous [e.g., wolf] animals, used to tear flesh from 
bone, and in herbiverous [e.g., mountain gorilla] animals, to help grind 
up leaves.)

	So, if an animal wanted to considerablely lessen its total mass
without losing the function of said massive structures, a beak would be
a particularly good development.  Beaks are strong, light, and weigh
very little.  The one thing they can't do is chew food, so the addition
of a few pebbles, etc., to a gizzard does the job.  The beak made the
large jaw, and the large bones which support the muscles to operate the
jaw, unnecessary. 

	Finally, I would argue against your friend's theory of beaks
developing because of no front limbs (or, at least, modified into
wings).  If this were true, then we could expect to see snakes with
beaks.  Or maybe some bats would, too (since the snake has no front
limbs, and the bat has wings).  I would further say that though the beak
seems to do very well as a food-gathering device, it wouldn't be the
best thing to have, over all other structures.  It's rigidity makes 
some types of food almost impossible to get.  Take, for example, one of 
the finches that Darwin first discovered in the Galapagos islands, which 
feeds on grubs underneath the bark of trees.  The finch had to get ahold
of a sharp stick or needle, and, holding it in its beak, use the needle to 
probe for the grubs.  True, this is a relatively new adaptation, and we
may find, thousands/millions of years down the road, that the bird has
develped a beak more similar to a woodpecker's.

	Other ideas?  Flames?

bryan sabol

anemoneman and ousted reedie-at-large