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Today's dinosaurs--the birds--have a uniquely avian piece of anatomy called the syrinx, located at the base of the trachea. Because it is located at a point where the trachea branches to the lungs, the syrinx makes birdsong a possibility.

The syrinx is an anatomy unique to birds--the non-avian dinosaurs, apparently, didn't have it--which makes it a competitor against that other vocal organ, the larynx.

Is it possible for one animal to have the syrinx AND the larynx in one body? If no, then why not? If yes, then what would the advantages of having both vocal organs be?

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    $\begingroup$ As an interesting side note, research on the evolution of the syrinx is ongoing. That page also comments on how "surprisingly, there has been no focused research in any field to illuminate [the evolution of the syrinx]". $\endgroup$ – Draconis Sep 17 '15 at 0:04
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I would say it is very unlikely for an animal to have both of them. I say this because the primary reason for both of them is to produce sound. Having either one satisfies this need. Animals learn to deal with the noise makers they have to make the sounds they need. If they can't make a sound then they really don't need it to survive. This is not to say some strange occurrence might not allow it, but if so it would be for a true need to be able to differentiate different kinds of sound. An amphibian life form might have a need to make sounds differently underwater and above water...

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Actually, birds do have both: a larynx high in the throat and the syrinx (often called the inferior larynx) down near the bronchial tubes. Bird larynxes are not used to produce sound, and may be vestigial; I couldn't find much information on them at all. I think it's safe to assume that syrinxes evolved fairly late — possibly as a side effect of the respiratory adaptations birds made to optimize the exertions of flight — so it's likely that there was some ancestral proto-bird species that had both a functional larynx and a functional syrinx. But it's a duplicate function, and the syrinx is a superior organ for producing sound: it produces a greater range of sounds than a larynx, and incorporates many of the 'sound shaping' features that in mammals require the involvement of lips, tongue, palates, throat, etc. Since the larynx adds nothing unique to the combination, there's no advantage in maintaining its function.

If a species did have both as functional organs, it might allow for more complicated vocalizations: e.g., tri-tonal sounds (some birds can already produce two sounds at once by differential use of each side of the syrinx), or odd sound effects (think Peter Frampton singing through his guitar). But since most of the sound would be formed before the air hit the larynx, the larynx would be a post-processing instrument, not a primary generator.

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  • $\begingroup$ natural voice changers $\endgroup$ – Topcode Apr 18 at 2:52
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possible it is, but not for long

You see, it is already believed that the syrinx came to be by two possibilities: mute dinosaurs which developed it (most unlikely) or dinosaurs,which, like every other animal, had a larynx, but developed a syrinx and then lost its larynx. The reason for that is simple: you don't need 2 structures that do the same thing especially when one seem to be better than the other. This theory of Dinos with both structures is the most accepted, and a good example why it's unlikely, there's simply no point.

Lastly, the advantages: maybe a larger array of possible sounds, but clearly not significant enough to justify its permanence in the organism, especially since we have birds that can mimic from other birds to chainsaws, cameras and guns with their syrinx alone, showing how effective it is.

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I would say no. Because excluding humans, other mammals have their larynx much deeper down the throat, somewhere close to the syrinx you mention. Having them both together in a close vicinity would be a waste of body resources as both would tend to create very similar sounds. So no, unless there is destined major creature redesign or a very very precise mutation (the chances of which are 0.000000000000000000001%), there is no chance of finding a creature which naturally has both the organs.

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    $\begingroup$ This is not correct, almost all other mammals (except koalas and some deer) have the larynx much higher up the throat than modern humans, see e.g. indiana.edu/~ensiweb/images/larynx.jpeg $\endgroup$ – Pertinax Apr 16 '17 at 16:12
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We honestly don't know.

Birds actually do have a larynx, and it does participate in vocalization, but not through the vibration of vocal folds (see reference below). But we have no idea as to whether a syrinx or larynx with vocal folds are mutually exclusive, how the syrinx first evolved, or what the two organs would function like together. Aside from a handful of extinct birds that have preserved syringes, sound-making anatomy is virtually unknown in extinct animals, and all extant species are either predominantly syrinx or predominantly larynx-with-vocal-folds vocalizers.

Non-avian dinosaurs, for all we know, could have had both. A lot of people, especially on the Internet, have been going around saying that dinosaurs “couldn’t” vocalize because of how the two traits are distributed in living animals, but that’s not how phylogenetic bracketing works. If an unknown taxon is bracketed by a living group with state B (crocodilians and turtles with vocal folds) and another group with state C (birds with a syrinx), the answer to the most parsimonious state for the unknown taxon isn’t state A (neither), it’s “uncertain”.

The broader problem is that vocal organs (e.g., a larynx with vocal folds) and the anatomy of the throat don't preserve in most fossils. An ossified syrinx occasionally preserves in the fossil record, but only rarely and it seems to be limited to Neornithes. However in order to evolve an ossified syrinx, you have to evolve an unossified one first, and we have no idea when that happened. Most of the Liaoning non-avian dinosaurs appear to lack an ossified trachea but Scipionyx apparently has cartilagenous tracheal rings. Pterosaurs and megaraptorid theropods have features (a pneumatized furcula) that today are correlated with features related to a syrinx (i.e., a clavicular air sac) in birds. So for all we know they did have an unossified syrinx. There is also evidence that hadrosaur crests modulated sound production, which means there had to be some precursor sound-making ability in order for selection to act on the sound-making function of the crests.

So the distribution of sound producing elements in Archosauria outside extant taxa is pretty much unknown. Maybe most dinosaurs had a larynx? Maybe most dinosaurs had an ossified syrinx? Maybe some had one, some had another, and some had no ability to vocalize at all? Maybe the reduction of the larynx as a functional element is due to the miniaturization trend in maniraptorans in general? We don't know.

Similar transformations of traits that seem "mutually exclusive" with animals having both features at once have been seen in evolutionary history. Synapsids went from a quadrate-articular jaw joint with the condyle on the cranium and the socket on the mandible to a squamosal-dentary jaw joint with the condyle on the mandible and the socket on the cranium, and went through a phase where both joints were functional at the same time (e.g., the cynodont Diarthrognathus) before the original joint gradually lost its original function and became part of the mammalian inner ear. If we didn't have these transitional fossils people might surmise that mammals evolved their jaws independently from all other tetrapods because these two jaw joints come off as mutually exclusive in function.

Another example can be seen in dinosaurs. Many dinosaurs and most crocodilians have only teeth, all birds today have toothless beaks. But many dinosaurs also have beaks, and some species have both beaks and teeth (e.g., most ornithischians, many maniraptorans). The problem is unlike teeth, vocal parts don’t fossilize.

This reference and associated references cited within does a pretty good job at summarizing the whole syrinx versus larynx debate, including references about birds having both.

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