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(Please note that this question is the sandbox version and the replacement of the original question)

I have been wondering about how humans require facial muscles in order to be able to produce speech, mammals also have these facial muscles that could allow them to speak if they had the brain power to produce speech.

Here is an image from the internet of a wolf skull and a human skull, along with another one that contains facial muscles:

Dog Skull Dog Facial Muscles

Reptiles however lack any facial muscles and therefore cannot move their face in any way, but I am wondering, what would the physical skull alterations be in order to have a carnivorous reptile with facial muscles sufficient enough that it could speak, and what would the reptile look like with facial muscles? How well would it be able to speak at this point? What is required for a reptile to be able to have facial muscles?

Skull of Lace Monitor Lace Monitor Lizard

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    $\begingroup$ Possible duplicate of What Would a Reptile with Facial Muscles look like? You were the one who asked that question, and used two of the same pictures. $\endgroup$
    – RonJohn
    Aug 31 '18 at 7:11
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    $\begingroup$ Is this the version that came out of the Sandbox? If so, you need to explain that and indicate that it supercedes the previous question so that people don't become confused. (If not, it's a duplicate.) $\endgroup$
    – Join JBH on Codidact
    Aug 31 '18 at 7:16
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    $\begingroup$ Applied your suggestions. $\endgroup$
    – user202315
    Aug 31 '18 at 7:37
  • $\begingroup$ I retracted my VTC. $\endgroup$
    – RonJohn
    Aug 31 '18 at 20:03
  • $\begingroup$ The face has very little to do with speech, it is mostly the throat and tongue, that is why parrots can speak even with a beak, and chimps can't, even though they have the same facial muscles as us. If replicating human speech is the only reason you are looking for facial muscles all you need is lips which has actually evolved more than once and there is not much too it. $\endgroup$
    – John
    Sep 1 '18 at 4:17
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If your goal is to have a speaking reptile, you need to know what is required to speak. Since reptiles are so numerous and diverse, I'll use a monitor lizard in this example.

First of all you need some vibrating membrane to produce a sound. In humans and mammals the vocal cords situated in the larynx fullfill this function. The larynxes of reptiles seems to differ quite considerably between species and while some can broduce chirping or growling sounds, others can only hiss. There must be muscles in the larynx that can put the vocal cords under tension to make them vibrate when air passes through.

From the larynx the sound travels into the oral and nasal cavity. The form, size and composition of these cavities influences the base tone of the voice. Have a look at this artificial mouth built by japanese scientists.

If a human opens their mouth and produces a tone, it sounds like an "ah". Due to the elongated skull and wide mouth, a lizards base tone might sound more like an "eh".

How their muscles have to change

Here's a complete list of every muscle that is somehow involved in producing speech. All muscles for mandibular movement should be present in a lizard, so let's concentrate on the muscles in the anterior face.

Monitor lizards have very thin lips with near to no muscles. The biggest muscles that move a humans lips are: Orbicularis Oris, levator labii superioris, depressor labii inferioris, buccinator and levator anguli oris. These would make the lips and cheeks of a lizard more fleshy and voluminous.

A special role plays the Orbicularis Oris. It's a ring muscle from the center of the upper lip to the center of the lower lip that pulls the corners of our mouth towards each other when we speak an "Oh". The elongated skulls of lizards make that quite a long route, so they either need very stretchy skin or shorter skulls to be properly able to speak.

How their skull has to change

Many muscles have to be attached to bone and the bone has to be in the right position for them to function properly. This would influence the skull of a monitor lizard quite strongly.

To produce the U and I sounds, the mentalis and depressor anguli oris need to shape the lips. These muscles have to be attached to a chin, which lizards lack. Their lower jaw would have to be much thicker, especially at the tip, and their skulls would loose their wedge-shape.

Pronouncing an F might be hard for lizards due to their big tooth gaps. You can come close to an F by pressing air through a small gap between your lips (almost like whistling), but it sounds distinctly different.

How their tongue has to change

I'm honestly not sure about how many differently oriented muscle fibers a lizards tongue really has, but with a forked tongue they probably won't be comprehensible. To produce K and T sounds, their tongues need to block the air completely, so the slender tongues of lizards are not suitable. They need a thick, fleshy tongue like that of aligators.

The result

People have thought about speaking lizards a lot and came up with different plausible ideas. Have a look at Draco from Dreagonheart:

Draco Face

He has a short snout, fleshy lips and cheeks and a flat, fleshy tongue. See him speaking in this video (Fast forward to 2:30).

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  • $\begingroup$ I also asked in my question about what changes they would have to undergo to also produce human-like facial expressions. $\endgroup$
    – user202315
    Sep 1 '18 at 1:30
  • $\begingroup$ @user202315 That would be a very different question I suggest you ask it separately. $\endgroup$
    – John
    Sep 1 '18 at 4:20
  • $\begingroup$ You don't actually need lips to make the "Oh" sound parrots can do it just fine, "B" and "P" really do need lips. Also reptiles don't have the same jaw manipulation muscles are mammals, the jaw and its musculature is one of the major changes in mammals and not just becasue of chewing. The jaw musculature of mammals is almost entirely different than reptiles. $\endgroup$
    – John
    Sep 1 '18 at 4:41
  • $\begingroup$ @John I ommitted changes in the jaw musculature based on the assumption that speech would be possible for a reptile with the current set of muscles. How much influence do the jaw manipulation muscles have on speech and pronounciation? $\endgroup$
    – Elmy
    Sep 1 '18 at 6:13
  • $\begingroup$ @YElm The ability to roll the jaw forward and back and cheeks are fairly important, at least in humans again in its not the only way to do it, parrots do something completely different. but really my problem was with the statement that "all the muscles for mandibular movement would be present" which is just flatly wrong. $\endgroup$
    – John
    Sep 1 '18 at 12:07

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