What is up with Tyrannosaurus lips?

[HD-man]

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?

See Keillor's "Jane, In the Flesh: The State of Life-Reconstruction in Paleoart" (Chapter 7 of this book: http://www.amazon.com/Tyrannosaurid-Paleobiology-Life-Ralph-Molnar/dp/0253009308 ).

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?

Not necessarily ("That's a great question. Spinosaurs and crocodilians with a similar notch are usually thought to have used it to catch fish, and it's possible that Dilophosaurus did so as well. But it seems like a lot of the coelophysoid-grade theropods have such a notch (though its strongest in Dilophosaurus), so maybe it's more related to picking up small prey items, and fish were just one of many targeted for munching on": http://scotthartman.deviantart.com/art/New-look-Dilophosaurus-553959249 ).

[Dinoguy2]

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


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

It's obvious even in this drawing that the teeth are dangling out of their sockets. You can see the roots!

There's also no reason the mouth would close all the way. In modern reptiles the mouth, when closed, looks more like the Ceratosaurs. The skeletal jaws are slightly agape, but between the gums and lips the mouth is sealed closed. In most modern reptiles the mouth would not even be capable of closing as far as usually depicted for dinosaurs.

[Tyto_Theropod]

Conclusion: Artists are far too obsessed with finding ways to show off how sharp Theropod teeth were.

[DinoLord]

The teeth wouldn't actually articulate that way (large portion of roots extruding from the socket) in life - the fossils appear that way because the soft tissue surrounding the roots decomposes after death and the teeth then become loose in the sockets.

[gfxtwin]

So is it more likely that most therapod's teeth were not exposed unless their jaws were open?  I see how it might make sense for carnotaurus and definitely Dromaeosaurs/raptors, but skulls of some therapods (Ceratosaurus is a good example) depict teeth that almost reach the bottom of the jaw when jaws are shut (even when you subtract the length of roots).  Unless the space between the lower jaw's gums and cheeks/lips for the upper jaw teeth to rest in was insanely deep, or maybe most therapods never closed their jaws, it isn't possible for the teeth to fit inside lips/cheeks, right?  I mean, T-Rex in particular had jaws that were meant to bite down with megaton force so wouldn't its bones have evolved a design to allow them to clamp together completely? 

[Doug Watson]

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).

Not being argumentative here but I had never heard that reasoning do you have a reference for that? I wonder then how dolphins and whales deal with the even greater pressure on their jaws at the depths they hunt at.

[stargatedalek]

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).

Not being argumentative here but I had never heard that reasoning do you have a reference for that? I wonder then how dolphins and whales deal with the even greater pressure on their jaws at the depths they hunt at.

I honestly don't remember, I'm probably mistaken. But I think it was about the speed at which they opened, and not that they opened, or perhaps it was about lunging through the surface. That being said most aquatic animals have functional "lips" (even most turtles can at least seal their mouths shut) except for ambush ones (crocodilians, snapping turtles, morays), so perhaps there was some reasoning behind it that I heard somewhere and have since forgotten.

Or perhaps it's because ambush predators don't care about lost hydrodynamics. I genuinely don't know.

[Lanthanotus]

Water pressure works into every direction for the exact same measures, so the argument of a mouth being sealed shut by the pressure would encounter the exact contoversial argument, that water within the mouth would prevent closing it; water pressure sealing a mouth shut would also mean water pressure would press any submerged animal down to the ground of the lake/river/ocean - neither of it is true. In fact water pressure is only relevant when gases come into play, as we are all made of water (for a higher or lesser percentage) our bodies can't be compressed by water pressure nor are any of our movements be hindered by water pressure just by its density which is practically the same just below the surface as in 11 km depth. This is way fish (or other beings) can move as quick in great depths as they can near the surface, but never as fast as on land or rather in an air filled environment (deep sea fish just often seem sluggish, because of their exothermic metabolism and the surrounding low temperatures). Just our gas filled lungs and the gas "dissolved" in our blood may cause us trouble in depths resceptively when goin' up again. 

[suspsy]

Mark Witton just wrote an excellent piece on this topic:

http://markwitton-com.blogspot.ca/2016/10/exposed-teeth-in-dinosaurs-sabre-tooths.html?m=1

[Patrx]

Mark Witton just wrote an excellent piece on this topic:

http://markwitton-com.blogspot.ca/2016/10/exposed-teeth-in-dinosaurs-sabre-tooths.html?m=1

Thanks for sharing, this is a fascinating topic!

[suspsy]

Yeah, it's easy to forget that there was once a time when paleoartists regularly employed lips on theropods.

[Dinoguy2]

Yeah, it's easy to forget that there was once a time when paleoartists regularly employed lips on theropods.

Witton makes the same point I was trying to above in a better way: animals don't close their mouths as far as dinosaurs are often shown. Showing a dinosaur with mouth closed as far as the bones allow to the point that the jaw bones would be touching at any point along their length is basically a symptom of extreme shrink wrapping. The jaw muscles in the corner of the mouth and the gums in the front would NOT allow the teeth of even a T. rex to overlap much with the bones of the jaws when the mouth was closed. This doesn't prove lips, but it removes the need for the only good argument against them.

[JohannesB]

Yeah, it's easy to forget that there was once a time when paleoartists regularly employed lips on theropods.

Witton makes the same point I was trying to above in a better way: animals don't close their mouths as far as dinosaurs are often shown. Showing a dinosaur with mouth closed as far as the bones allow to the point that the jaw bones would be touching at any point along their length is basically a symptom of extreme shrink wrapping. The jaw muscles in the corner of the mouth and the gums in the front would NOT allow the teeth of even a T. rex to overlap much with the bones of the jaws when the mouth was closed. This doesn't prove lips, but it removes the need for the only good argument against them.

Does this negate the argument against lips by the scientific consultant of the PNSO Tyrannosaurus rex model, in that video, when he indicates how the teeth of the lower jaw would fit into holes in the upper jaw and thus protecting the teeth in the lower jaw? Since, if the teeth in real life would not be able to overlap much with the jawbones when the mouth was closed, then the newest PNSO Tyrannosaurus model is wrong in that regard as well. (In that model, when the mouth is closed, the teeth in the upper jaw protrude almost as low as the underside of the lower jaw!)

[stargatedalek]

Yeah, it's easy to forget that there was once a time when paleoartists regularly employed lips on theropods.

Witton makes the same point I was trying to above in a better way: animals don't close their mouths as far as dinosaurs are often shown. Showing a dinosaur with mouth closed as far as the bones allow to the point that the jaw bones would be touching at any point along their length is basically a symptom of extreme shrink wrapping. The jaw muscles in the corner of the mouth and the gums in the front would NOT allow the teeth of even a T. rex to overlap much with the bones of the jaws when the mouth was closed. This doesn't prove lips, but it removes the need for the only good argument against them.

Does this negate the argument against lips by the scientific consultant of the PNSO Tyrannosaurus rex model, in that video, when he indicates how the teeth of the lower jaw would fit into holes in the upper jaw and thus protecting the teeth in the lower jaw? Since, if the teeth in real life would not be able to overlap much with the jawbones when the mouth was closed, then the newest PNSO Tyrannosaurus model is wrong in that regard as well. (In that model, when the mouth is closed, the teeth in the upper jaw protrude almost as low as the underside of the lower jaw!)

Yes, in fact the PNSO rex also just has teeth that are far to long to begin with that extend out of the jaw further than they would have in life.

[Bowhead Whale]

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.

I think you're right. Just look at elephants and walruses, for example. They do have lips, but their extremely long incisors (elephant) or canines (walrus) do largely extend the lips' limits. Just like the canine teeth of the male muntjac. All those animals have lips, but also have teeth that are visible even when the animals close their mouths. Why couldn't it be the same with a few dinosaurs?

[stargatedalek]

Look again at that Dilophosaurus skull. Look at the shape of the teeth. Notice how they start straight then begin to curve? The straight part should be completely embedded within the skull, not even the gums, but the actual tooth sockets in the skull. They slide out of those sockets after an animals has died and not everyone accounts for this when reconstructing fossil skulls.

Only the part after the tooth starts to curve should be visible extending out of the skull, and a bit more yet should be covered by the gums and the various tissues on the skull, even before actual lips to close the mouth.

[Bowhead Whale]

Look again at that Dilophosaurus skull. Look at the shape of the teeth. Notice how they start straight then begin to curve? The straight part should be completely embedded within the skull, not even the gums, but the actual tooth sockets in the skull. They slide out of those sockets after an animals has died and not everyone accounts for this when reconstructing fossil skulls.

Only the part after the tooth starts to curve should be visible extending out of the skull, and a bit more yet should be covered by the gums and the various tissues on the skull, even before actual lips to close the mouth.

So, the straight part of the tooth was covered with gums. Logical.

[stargatedalek]

Look again at that Dilophosaurus skull. Look at the shape of the teeth. Notice how they start straight then begin to curve? The straight part should be completely embedded within the skull, not even the gums, but the actual tooth sockets in the skull. They slide out of those sockets after an animals has died and not everyone accounts for this when reconstructing fossil skulls.

Only the part after the tooth starts to curve should be visible extending out of the skull, and a bit more yet should be covered by the gums and the various tissues on the skull, even before actual lips to close the mouth.

So, the straight part of the tooth was covered with gums. Logical.

It was not covered with gums. It was inside the skull. The straight part of the tooth is only visible as an artifact of the fossilization process, it wouldn't even be there on a fresh skeleton. Subtract that portion from the length of the teeth to get an accurate tooth size.

[Faelrin]

That's kind of like how the roots of our teeth can show up in our sinus cavities/much longer then what we initially can see in our mouths. That's a fair comparison correct?

[stargatedalek]

That's kind of like how the roots of our teeth can show up in our sinus cavities/much longer then what we initially can see in our mouths. That's a fair comparison correct?

More than a comparison, that is literally what this is. They just had straight roots instead of splayed ones like we have.