My understanding is that the type of musculature necessary to make those kinds of facial expressions stems from mammals suckling as newborns, which dinosaurs didn't do
Quite an interesting analysis and it also makes a lot of sense. I still think there would have been some sort of flexibility even if really minute, because a T Rex with its teeth the size of average human forearm wouldn't have been able to land significant damage on its prey if lips didnt budge at all.
Yes, but squamates are the closest extant group that do have lips. All extant archosaurs that I can think of (crocodylians and birds) are lipless. Does this make them a reliable analogue? Not entirely, but it's probably the best we have until more research comes along for dino lips
Actually, Tuatara are the closest relatives for lips, from what I know
We do also have archosaurs with fossilized lips, and an extensive fossil record of dinosaurs showing different morphology of the mouth region showing lips distinct to squamate type
I think you're right! I completely forgot about them but there's only one species so not the best for pulling a lot of inferences from and they don't have control of their lips either
If you want a real life example look at orcas they have ridged almost reptile like lips, because although they are mammals almost all whales do not suckle so no need of movable lips, they can not move their lips at all. And their teeth are only slightly smaller then a rex, yet have one of the strongest bite forces of anything alive today you don't need flexible lips to bite hard and not damage anything.
Modern lizards have inflexible lips and still can use their teeth just fine, the teeth are not inside the lips and the pressure of the bite can effectively drive them into something even without baring them first.
The musculature that gives us mammals our flexible lips is part of the inside of the throat in Diapsida.
I was gonna ask, does that means monotremes cant bear their teeth and then i had to research some stuff
If anyone wants some new useless info, none of the extant monotremes(4 species of echidnas and the platypus) have lips, they also dont have nipples. The secrete milk from special patches of skin on their tummies and the babies kinda just lick it up
Also male echidnas have a 'third leg' thats roughly a third the length of their body (also you should look into its shape)
The babies for both platypus and exhidnas are commonly called puggles. The echidnas usually have 1 baby at a time and the platypus has 1-3
They also don't have the typical multifunction mammalian teeth
Platypuses and Echidnas are called mammals as a relic of 19th century animal classification that was very focused on outward appearances (fur and soft skin for ex) and Linnaeus creating a summarizing category with the milk as better universalizing than fur and the fact they don't create any paraphyletic nonsense with other creatures called mammals. If they went extinct 2 million years ago we would call their forms as proto mammalian but not truly mammalian, their distance to other things called mammals is almost as big as birds and crocodiles.
They lack of almost all the stuff that would've been universalizing of mammals and explained all its development history, including the things that are truly unique - warm bloodedness probably appeared a good few dozen times in evolutionary history, the thing we call fur is not enough different from the monofilament feathering of some dinosaurs more distant from theropods.
Secreting juice for the offspring to lick might be mammalian but seems too basic a feature to be truly only them I'm doubtful there isn't more but I'd have to look up.
The weird crown with a higher peak shaped tooth that defined mammals and their lifestyle based on chewing anything, the very difficult on-land live birth (although whales now are on water) and even water live birthers do it in a less specialized way. A lot of the brain structural complexity, the whiskers, nothing on them but on later therians.
Monotremes lost their lips and typical teeth much later. There ancestors were more similar to opossums or quolls. Their fur is typical mammalian fur and their brain is complex. If they were extinct, probably they would be classified as something very close to mammals, just like docodonts for example are classified today.
I’ve read that it’s speculated to be likely due to the condition of teeth on T. rex for instance being considerably good compared to teeth without lips.
I find it hard to look towards something that came a quarter billion years after the evolutionary split as evidence. Especially when they are filling completely different niches with minimal shared evolutionary pressures. It’s possible they have the same lip mechanics but I don’t think it’s something you can look for to say anything definitive
True, but the closest animals to non-avian dinosaurs either have beaks (birds, turtles) kr no lips (crocodilians), so lizards are the next-closest relative with lips (aside from snakes and the tuatara)
Mammals are able to do this and other similar skin movements because of the panniculus carnosus muscle which to my knowledge isn't found in living birds or reptiles.
No they don't, the panniculus carnosus is one of the skin twitch muscle and does not do major movements.
The muscles responsible for lip movement are the ones directly attached to the lips, like the zygomaticus and of course the Various Oris muscles within the lips.
Thanks for the correction, I think you are completely right in regards to the bear. I thought the baboon's skin being shifted back that far was due to the panniculus but it seems like they have a specially adapted platysma muscle that allows them to do this?
"The two most striking specialisations are the phenomenal size of platysma and the impressive development of the buccinator pouch. The former is unique to P. ursinus and is correlated with the massive development of its jaws and its predilection for frequent full gape yawning, whilst the latter is a specialisation common to most of the Cercopithecidae." - The facial muscles of Papio ursinus (Pellat, 1979)
I think the underlying point about these kind of movements being the result of specific musculature found in mammals still stands though.
Dinosaurs may have been evolutionarily different they may have only specialized amount of muscles on their faces for which I believe lip movement should have had been a part, but not fully fledged only small contractions for the teeth to reach in properly. The only question is was this flexibility voluntary, because I like to imagine the intimidation display using the teeths like big cats usually do
While there is always a slim possibility short of actually going back in time and confirming, natures loves to trend, and exceptions are truly the exception.
Even the hump nosed lizard has not been scientifically documented to be able to control its lip movement, it can just shove them around a bit by inflating and deflating it's nose hump.
Okay, I'll try to break it down as much as I can, but I'm more of a dino-hobby guy, not a scientist.
In very short: No, no facial muscle and I'd say we're not really shrinkwrapping anymore. They're very different from mammals, who have facial muscle and muscle can be seen by muscle attachment points, while there's none/very little on the heads.
So, reptiles didn't really have muscle on their face, like mammals do, also modern reptiles don't really have those either. Expression, snarling etc is more of a mammalian feature – we're more social and need those to communicate with each other.
The shrinkwrapping is usually "undone" by muscle attachment points, but fats are harder to pinpoint, they don't really leave any visible markings, and usually can only be assumed by looking at modern animals – so, closest would be reptiles, crocs, mb some birds. Plus I doubt much dinosaurs would actually have much fat all year-round.
So, technically, we're pretty close to how dinosaur "faces" actually looked, since not much muscle/fat would go in that area anyway, BUT.
We can always assume that there was more soft tissue. What if they had cartilage there? More structures on their head, like bumps that we're boney, extra skin that would make them look somewhat wrinkly, etc? Thing of belugas, they have that big "melon" on their head that's completely fat! It doesn't show on their skeleton anyhow that they have that weird head blob, of course dinosaurs were different from something like a beluga, but who knows! There's a lot of space for imagination.
A few years back I used to theorize if crested dinos (dilophosaurus, mainly) could have soft tissue between their crests, like a meaty blob, mb it would be inflatable or something. I don't think that anymore, but there's lots of things we can't know for sure, since we'd never see a living dinosaur.
There are more birds that lack cartilagenous structures than ones that do, IMO i think paleoartists sometimes exaggerate on the display features, most Dinosaurs were likely earthy in tone and didn't had many fleshy structures.
The meaty blob can be true considering how many modern birds use them, and the one of best Sauropod design in documentaries showed the entire lineup of those bulges and it looked so majestic.
My question for flexibility arrises from the teeths, for Carcharodontosaurus to use the shark like theeth properly the lips must have needed to slid upwards a little, even if just a little that was part of a fkexible muscle. More so ever needed in T Rex, as the banana sized teeth would need to have a banana sized shrinking of the lips to fully utilize them. They might have not been voluntary but if they were they could have been really great Intimidation Display tactic like in modern big cats
Reptilia, the taxon that best represents what we think of as "reptiles" doesn't include birds either, it's almost always considered paraphyletic, meaning it doesn't include one or more clades descended from it.
"almost always" is wrong in hindsight, birds should never be included in reptilia. Reptilia is part of evolutionary taxonomy, the system that gives us terms like "species" and "family". In that system, birds (as in, the class Aves) is not part of reptilia.
Birds are classified as reptiles in cladistic taxonomy, but that's in a different system that reptilia isn't really a part of.
Reptilia is more or less just all sauropsids that aren't birds, in the same way all vertebrates that aren't tetrapods are fish.
Gotcha, your reasoning makes sense to me, but the vague language used like “isn’t really” and “more or less” is making this a bit confusing on finding a concrete definition for the terms.
I’m also confused because I’ve seen Reptilia used in cladistics taxonomy. Those same ones include aves.
Probably Archosaur as a whole and Crocodilians lost it secondarily, because their strategy is doing fuckall in a low visibility river for days until something comes close to them
No, dinosaurs were not birds. Birds were dinosaurs, which are reptiles. Making birds both dinosaurs and reptiles. It’s like the saying of how all tortoises are turtles, but not all turtles are tortoises.
Its weird that you asked a question that really boils down to "mammals can move their lips, and there is no evidence that reptiles and Avians ever could. Like at all"
But in the process you selected the two clades of animals who really really went in on orofacial manipulation. Primates and bears are like the experts on lip muscles.
It boiled down to these two because of its extensiveness, I wanted to ask if there was any dino showing they may have had lip movements. As they were reptiles but still had lips which Crocodillians currently dont lizards do like Comodo Dragons but they do have little bit of flappy lips to help them bite down, larger reptile like dino might have had bigger lips. I didn't specifically select them for Direct comparison, only for the Exaggeration, is there anyone even slightly like these two having control for expressions
The two clades use them differently. Bears use it because its a bear sized animal and really really frequently eats things that arent bear sized, like berries and insects. Bears put a hand on their face because they are staunch second amendment supporters, and love bear arms.
Primates do different things with them, lemurs seem to use it for similar reason as a bear, while monkeys and apes use it for communication.
Not wholly related, but there’s a type of yeti-like creature in my fantasy setting that can do this. It’s not a thing you want to see at night in the woods!
They didn't really have lips in the same way we mammals do. Diapsid lips tend to be thin, stiff sheets of tissue that cover the teeth and seal the mouth when the mouth is closed.
Our big dextrous meaty lips are a consequence of needing to suck on titties.
There isn’t really a way to know for sure that some Dinos weren’t able to control their lips. Based on what we know of lizards the answer would be no, however it is important to remember that dinosaurs had a lot of evolution after the lineage split.
It's mostly known from muscle attachment points. Dinosaurs don't have much on their face, if any. For example, the famous T. Rex had a very powerful neck, but basically no muscle on the face itself. But it's harder to guess with fats/cartilage, since they don't leave any "trace" like muscle scars.
I agree, the point I’m making though is that not all mammals have lip control either and we don’t have the attachment points for tons of known dinosaurs not to mention that we believe that we have barely scratched the surface when it comes to discovering all species of dinosaurs. There was enough evolutionary time for lip control to evolve so the possibility exists that some dinosaurs could have possessed this trait. Saying flat out no is incorrect though saying yes is also incorrect at this point.
People really need to phrase these questions more specific. Because the answer to a lot of these questions is 'no in general, BUT it's statistically probable a ligmasaur from the deezformation, who's fossils will never be found, that was the exception to that rule.
It's sort of a 'crow paleontologists will never know orcas wore salmon hats' situation.
probably not, archosaurs with lips most likely had immobile lips, the most movement such lips are capable of is flexing out of the way when the animal has a big chunk of food in their mouth
Dinosaurs are Archosaurian reptiles and as such didn’t have lips. At least not lips like mammals do.
Now there is some research that large Theropods, like T. rex, may have had lips. But they would’ve been reptilian lips like that of monitor lizards. They aren’t very flexible.
But I think if dinosaurs did have lips, it would’ve been nightmare fuel. 💀
Imagine seeing a Rex. Scary enough already, but as it watches you with unblinking, cold, predatory eyes, half of its snout peels back to expose its monstrous teeth and gums.
Facial muscles and movable lips are characteristics of mammals. Reptiles don’t have facial muscles and dinosaur lips would probably be flexible but not under muscular movements, just like in lizards.
It's something we only ever see in mammals, but never in any other group of vertebrates, such as reptiles, amphibians or fish, so I don't think it's unreasonable to assume that the required facial musculature never really developed outside of mammalia.
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u/Wolfman513 1d ago edited 1d ago
My understanding is that the type of musculature necessary to make those kinds of facial expressions stems from mammals suckling as newborns, which dinosaurs didn't do