What is up with Tyrannosaurus lips?

[TomWToyForum]

Something from not long ago was the idea that Tyrannosaurus had teeth so large that it was impossible for it to have lips. I remember the particularly humorously titled thread *FLASH* Sue the TRex GUMS a Torosaurus to Death!! (by Galileo) a few years back, but lately I've been seeing an influx of lipped Tyrannosaurus pieces from artists like John Conway and Mark Witton.
Is there something recent I missed, or is it not as clear-cut as I thought?

[tyrantqueen]

We don't have any fossils to say one way or the other. Tracy Ford wrote a really good article in PT about it. I've seen it vary from artist to artist.

[stargatedalek]

Basically it all comes from inferences of modern animals. There isn't a single living animal that doesn't have gums/lips that cover its teeth when the mouth is closed without a very specific reason. A few mammals have highly enlarged teeth that are used for feeding, digging, fighting, or even display, and these are the only terrestrial animals you'll see showing any teeth with the mouth comfortably closed. Crocodilians have jaws with their teeth visible to prevent their mouths from becoming sealed shut by water pressure (which would make ambush very difficult since it would take some effort to force the mouth open). Birds (and turtles) for obvious reasons can't be referenced for the mouths of most dinosaurs.

[Rain]

Basically it all comes from inferences of modern animals. There isn't a single living animal that doesn't have gums/lips that cover its teeth when the mouth is closed without a very specific reason. A few mammals have highly enlarged teeth that are used for feeding, digging, fighting, or even display, and these are the only terrestrial animals you'll see showing any teeth with the mouth comfortably closed. Crocodilians have jaws with their teeth visible to prevent their mouths from becoming sealed shut by water pressure (which would make ambush very difficult since it would take some effort to force the mouth open). Birds (and turtles) for obvious reasons can't be referenced for the mouths of most dinosaurs.

I'm assuming you aren't including fish in this list, correct? Cause I can think of plenty of fish which have uncovered teeth for no apparent reason, either that or I don't know enough about them heh

[stargatedalek]

Haha that is indeed true

I forgot to mention terrestrial vertebrates didn't I? Yup, I said all animals, my goof

[TomWToyForum]

Thanks guys! I heard the no-lips thing stated as a fact in a program from about ten years ago or so, but I couldn't recall the title.

[antorbitalfenestrae]

Jaime Headden has some good discussions of the portrayal of lips in dinosaurs. https://qilong.wordpress.com/2011/09/18/making-lip-of-it/ This is one article from a while ago about theropods, but he has plenty of other ones that talk about the topic (with some interesting ideas about ornithischian lips and 'cheeks').

[Lanthanotus]

Jaime Headden has some good discussions of the portrayal of lips in dinosaurs. https://qilong.wordpress.com/2011/09/18/making-lip-of-it/

Thanks for the very interesting link, just ran over the text yet, but the comparisons and ideas of the author are quite accurate. Personally I deem it highly likely, that most if not all theropods had lips, even the ones with enormous teeth as T. rex. One reason why I love this "outdated" renderings: Klick!

In recent monitors the comparably large teeth are even hidden within a deep gum and what you see when they open their mouth is just the tip of teeth. During vicious bites the teeth hurt the gum and may start a bleeding but the reasons for this are debated: For example it may help to infect the wound of the prey - monitor blood is full of microorganisms that you don't want within your blood circuit. This however only makes sense when the animal hunts prey much larger than itself and a direct fight would bring a high risk - as it is in the Komodo Dragon.... or lot of gigantic theropods. Maybe some hunted actively, but "only" slashed their victims and then waited hours or even days until blood loss and infection weakend the prey?! Well, that's another topic.

[Tyto_Theropod]

It is is, but I should point out that the idea of Komodo dragons simply using the bacteria they pick up in their mouths is an outdated idea. It's now known that they're venomous, and we have no (compelling) evidence of any venomous dinosaurs. While I imagine that the grooves and serrations in Theropods' teeth could have held onto bacteria and this could have indirectly killed their prey through infected wounds, I doubt it was an intentional thing or particularly selected for by evolution.

[stargatedalek]

Very few monitor species are venomous however so I don't think that's relevant to their lips.

[Tyto_Theropod]

Very few monitor species are venomous however so I don't think that's relevant to their lips.

It isn't. I was pointing it out to Lanthanotus.

Crocodilians have jaws with their teeth visible to prevent their mouths from becoming sealed shut by water pressure (which would make ambush very difficult since it would take some effort to force the mouth open).

With their enormous, splayed teeth, I did wonder when I read this if Spinosauridae could have had a similar mechanism. Oh well, guess we'll never know...

[Dilopho]

And then you get to ceratosaurids with their ridiculously giant and terrifying teeth:


(Dilophosaurus is a ceratosaurid, right? Am I mistaken?)

[antorbitalfenestrae]

(Dilophosaurus is a ceratosaurid, right? Am I mistaken?)

I'm pretty sure it's a coelophysid, but I could be wrong there

[Lanthanotus]

Despite being a bit off topic - as said before - I cannot come around to answer

It is is, but I should point out that the idea of Komodo dragons simply using the bacteria they pick up in their mouths is an outdated idea. It's now known that they're venomous, and we have no (compelling) evidence of any venomous dinosaurs. While I imagine that the grooves and serrations in Theropods' teeth could have held onto bacteria and this could have indirectly killed their prey through infected wounds, I doubt it was an intentional thing or particularly selected for by evolution.

Many, if not all varanoid lizards have glands in their lower jaw which are considered venom glands by some authors. However, the connection of those glands towards the inner throat or mouth is under discussion and the saliva of monitor lizards (including the Komodo Dragon) seems not to contain any specific potent venomous substances that could not be found in a lot of other animal's saliva too, which do not have such glands. Being bitten by several monitor species myself I cannot report any specific venom reaction - aside from pains that could also be easily explained by the brutal force of even small species or the usual flora/fauna inhabting their saliva.

The serrations along some dinosaur and some monitor teeth are an interesting thing. Monitor teeth vary from species to species (and in some species even by age, despite being replaced through the whole life, so wear alone doesn't suffice for an explanation) from staight needle like teeth over teeth with relatively blunt tips and broad bases to the Komodo's serrated steakknife teeth. Each of these seems to have evolved in favor of a specific diet. For example,... despite being three times heavier and having an almost four times bigger skull, my roughneck monitor is'nt well capable to prey on hard shelled beetles which are no match for the much lighter and smaller skulled tree monitor. But the beetles can't be snatched up by the bigger monitor with it's backwards pointing teeth (ideal to hold on slimy prey as worms and slugs) as they tend to slide from his teeth when he enforces the bite, while the broad and chisle like teeth of the tree monitor easily pinch through the beetle's armor.

That being said,... the serrations on teeth not only help to cut the dead prey's meat, but they also produce much fiercer, frayed wounds that bleed heavily and heal badly, a fact that may have enforced the specific way of hunt the Komodo Dragon shows. But what was first, or what was more important to favor the evolution of steakknife teeth is a question quite hard to answer.

To close the circle back to the lips and their potential relation to venom and/or pathogenic germs.... the potency of both is bound to a humid or wet setting, meaning that lips, covering the teeth and closing the throat, allow a nice environment for infectious germs and providing a medium (the saliva fluid) for venom to flow into wounds (for those animals that do not have syringe like teeth as some snakes do).

While carnivorous dinosaurs undoubtly look cool with their horrific teeth being bare and open, the adavantages of having lips in land dwelling species are probaly much bigger than being lipless (lips prevent water loss, lips help to establish a homogenous climate for the throats flora/fauna which is a vanguard of the bodies immune system,...), so well, paleontology has some questions to answer in this way.

[Tyto_Theropod]

I wasn't meaning to argue that terrestrial dinosaurs didn't have lips, as I personally agree with you that the evidence is stacked in favour of lips being present in *most* of them (with exceptions like Spinosaurus, which as I pointed out may have had a mouth that functioned in a similar way to that of a crocodile's, as outlined by Star). I do however bow to your superior knowledge of monitor lizards. Last I'd seen the whole venom thing was pretty new, but after a cursory Google search I see that it is still being disputed and I'm inclined to trust you as someone who actually keeps monitors.

[stargatedalek]

I must say I'm very intrigued. It's been a long while since I've done any digging into monitor venom so last I heard it was expected to be restricted to Komodo dragons and their closest relatives (lace and megalania IIRC). I'd love to hear some more in-depth information about this, especially its implications for differences within Iguania and Anguimorpha evolution.

[Plasticbeast95]

And then you get to ceratosaurids with their ridiculously giant and terrifying teeth:


(Dilophosaurus is a ceratosaurid, right? Am I mistaken?)

I think Dilo's massively elongated teeth show that even if some theropod species did have large lips, they were not guarantied to have completely covered the teeth.

[Dilopho]

I wonder how Dilophosaurus dealt with the notch in it's jaw.
It might have been used for catching fish, but how was it covered? Was it covered?

[Tyto_Theropod]

I wonder how Dilophosaurus dealt with the notch in it's jaw.
It might have been used for catching fish, but how was it covered? Was it covered?

We may never know...

Although now that I look at the skull, it does seem reminiscent of Spinosaurus's 'fish trap', doesn't it? Perhaps Dilophosaurus was mainly piscivorous? Hmm...

[Lanthanotus]

When taking in account recent animals, the Dilopho's teeth design hints towards an evolution in favor of hunting some sort of "slippery" prey, may it be fish, amphibians or smooth scaled reptiles (like recent skinks). Considering the shown skull being accurate, the light build of the skull aswell as the long but fairly narrow teeth with their extremly backward facing tips makes is probable, that the animal fed on small to midsized prey. Even thick plumaged prey may have been easily to be snatched up with this dentition, though it may be questionable how far plumage evolution was when Dilophosaurus dwelled the earth - however, the Princeton Field Guide states Prosauropods and early armored ornithischians as prey (juveniles?)....?!