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Pardon my ignorance ... A lip is apparently a very sensitive tactile device - as it at-least serves to warn it's owner they may just be about to consume something that could cause injury. Primates (including humans), dogs, cats, sheep, buffalo, elephants, some fish, octopodes - to name a few, have a lip.

How have lips evolved to be nearly ubiquitous across animals? Why have they evolved into a beak/bill in some birds & fish? What niche/purpose do they fulfill?

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"Why have they evolved into a beak". Is this true? I would guess that lips and beaks evolved to perform occasionally similar functions, but from very different structures, and so lips have not evolved into beaks. –  Oreotrephes Jul 29 '13 at 23:45
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Maybe lips are (nearly) ubiquitous in extant mammals because they all inherited lips from a common ancestor. –  kmm Sep 25 '13 at 19:18
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2 Answers

I think what you are looking for can be found https://en.wikipedia.org/wiki/Lips#Functions_of_the_lips and https://en.wikipedia.org/wiki/Beak#Functions pretty easily.

To summarize, lips:

  • Mainly useful in mammals
  • Food intake
  • Articulation
  • Tactile organ
  • Erogenous zone
  • Facial expressions

Beaks:

  • Found in birds
  • Feeding
  • Defense
  • Manipulation of objects
  • Communication
  • Heat exchange
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What is a lip(s)? A set of muscles around an orifice that can close said orifice.

How about a way to close a hole so that not everything can get in but what we want - to eat, breathe, drink?

The fact that they are also sensitive is just needed so that you can more precisely operate them for whatever need you have.

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