Say we have an organism with the beak of a raptor (the bird type, not the dinosaur), but instead of a full beak, it only has a mandible on the upper jaw, while the lower jaw just has a jaw bone like that of a dog or human, would this be possible from an evolutionary sense or would the lack of a lower mandible make the beak useless.

If so, how would one make it work? Would it need teeth on it's lower jaw to compensate, or even teeth on the upper and lower jaw? There's a rough illustration below to show how I imagine it in its basest form. enter image description here

  • $\begingroup$ Think about crocodiles. They swallow food whole. They do "death rolls" to tears meat. Often they feed in packs. In a big enough feeding frenzy of "death rolling" beaks, maybe swallowable pieces can be ripped apart. $\endgroup$ – Just Someone Feb 2 '17 at 20:14
  • $\begingroup$ I don't understand your question. First, our lower jaw bone IS a mandible, so you need to correct your terminology. Second, consider beaked whales, tadpoles, and sirens (salamanders). All have beaks. Therefore, I guess the answer to your question is beaks apparently already exist in similar forms to what you suggest. If you have a more specific design/form issue, you need to articulate it. $\endgroup$ – Li Zhi Feb 2 '17 at 20:33
  • $\begingroup$ The mandible is the lower bone. Your first para doesn’t make sense: did you mean to use a different word here? $\endgroup$ – JDługosz Feb 2 '17 at 23:02
  • $\begingroup$ I think it's clear I meant the lower jaw part of the beak, if not from context clues certainly from the illustration. What would the correct word be? $\endgroup$ – ArborianSerpent Feb 2 '17 at 23:27

I assume you mean teeth like people/dogs have, and not teeth in the way that many birds already possess, right? Having evolved from reptiles, many birds do already have teeth. Ultimately the lower beak doesn't tend to do a lot more than house the tongue and those teeth. Here's one example:

enter image description here

Assuming you mean a species with large beaks and jaws that could support human or dog-sized teeth...

Case 1 - No Teeth on Either Jaw

If there are no teeth on either jaw, this animal is going to need to eat things without mastication. That would probably restrict it to soft meals like VERY soft fruits and/or worms. A diet of that sort does not lend itself to needing or being benefitted by a curved beak, so this case seems unlikely.

Case 2 - Teeth only on the Lower Jaw

If there are teeth only on the lower jaw they are not going to have anything to match up with or go around on the upper jaw. Tearing would be a challenge since all of the mechanical force would be on only one set of teeth, so the animal probably wouldn't be tearing at much meat. Grinding actions definitely require something for the lower teeth to mash up against, which really just creates an upper set of teeth (or tooth-like flats in the beak), so being a herbivore is out.

That leaves a diet primarily consisting of a wider variety of fruits and bugs than Case 1. For the amount of stuff that gets stuck in teeth and their likelihood of breaking though, I think this animal would probably be out-competed in the wild.

Case 3 - Teeth on Both jaws

In a very real way, this starts to feel like the question "would a dog or person be benefitted by having a beak instead of a nose?". The short answer is that if we are it isn't apparently worth the cost of production. That is evidenced by the fact that it doesn't exist anywhere.

Curved beaks in particular are used for ripping, tearing and shredding... things that a good set of teeth can already do. It's a duplication of effort, and that is not usually rewarded in nature.

  • $\begingroup$ If the lower beak doesn't do that much, could you just use teeth or other harder bits inside the mouth to hold a piece of meat and rip with the sharp curved beak like eagles do? $\endgroup$ – ArborianSerpent Feb 2 '17 at 17:16
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    $\begingroup$ Without a doubt you could. The issue, I think, is that with just one set of actual teeth you would end up putting a lot of strain on individual teeth. Many individuals might be just fine, but enough would probably break a tooth at some point that there wouldn't be any evolutionary advantage to using teeth (which are complicated to grow and maintain) versus a lower beak. But sexual dimorphism and lack of competition can overcome a lot of morphology that might otherwise be counterproductive. $\endgroup$ – GrinningX Feb 2 '17 at 17:26
  • $\begingroup$ What about this, it has a sharp beak for meat, and instead of teeth it has one whole curved piece of bone in the lower jaw, like a grinding stone, which it can grind plants and fruit with against the bony ceiling of the mouth. Would a whole piece of bone instead of individual teeth be less prone to damage? $\endgroup$ – ArborianSerpent Feb 2 '17 at 17:51
  • $\begingroup$ RE: "...many birds do already have teeth.." False. They have serrations on their bills or beaks which have the same function as teeth, but they are not true teeth. $\endgroup$ – cobaltduck Feb 2 '17 at 21:05
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    $\begingroup$ @cobaltduck - That's true, their not true teeth. They can (to a lesser degree, given size) perform many of the same functions, but they do not have the same complexity as teeth. They don't have to grow in - which can go awry - and don't meet up with softer tissue which can get infected if not maintained. That's actually a point I make regarding teeth not being likely in this situation. But it's a good call that what birds have are not, in fact, true teeth. $\endgroup$ – GrinningX Feb 2 '17 at 21:45

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