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RE: Making Lip of It



">   Large teeth with some form of "preservative covering" -- again, 
we're dealing with an untested argument, where the _teeth themselves_ 
must be >preserved in some fashion"

     I would think that dentine, also known as ivory, would be sufficient. 
After all, it's been used to fabricate all sorts of durable tools for thousands 
of years. I do remember reading something (was it David?) about fissures in 
African elephant tusks. I have to ask where this information came from and if 
it was actually demonstrated that it is caused by arid conditions and not 
something else. The only thing I found was a part in the book 'Wild Life Wars' 
where the author states that ancients tusks of long dead elephants tend to have 
fissures and cracks, where as tusks from recently killed animals or perfectly 
smooth. You can read a sample of chapter one on Amazon.

>where the teeth are so ridiculously large they might seem to argue 
against "lips" as well, such as various rodents. And while some rodents 
have >exposure of the distal tips of their incisors, this is very minimal
 in general.

    Using mammals as an example in this case borders on being a fallacy of 
equivocation: mammalian lips and reptilian lips or quite different; compare 
iguana lips with an elephant's trunk. However, If there were no living hippos>  
http://www.skullsunlimited.com/userfiles/image/category5_species_1614_large_2.jpg
 how would we know if their giant teeth were covered with fleshy lips? We could 
make inferences by looking at other mammals with very large teeth. We might 
also note that the teeth curve in a way that would allow large muscular lips to 
easily slide over and conceal them. Now on the other hand, if we looks at 
something like Dilophosaurus, Kaprosuchus, or Ramphorynchus would it be 
reasonable to argue that their mouths would have been able to support the 
comparatively simple, non-muscular lips of a lizard? I think such a structure 
would be useless for these animals. It makes more sense to me that they would 
have had hard scales covering the margins of their tooth rows: it would be more 
effective for preventing injury to the soft tissues of the mouth; I suspect 
this is the real reason that crocodiles are lipless.


"With teeth, does the enamel itself need to be protected, or can their be
 other methods, such as increased water intake, that can allow this?"

     Again, I think this may be an argument based on a false premise. There are 
more than enough examples of dentine being a durable enough material: teeth and 
tusks have been found intact that are thousands of years old; we have examples 
of many mammal lineages evolved exposed teeth independently; there were 
pterosaurs, many of which made a regular habit of soaking their teeth in 
saltwater. All this suggests to me that teeth are durable enough to exist 
without some sort of extra protection. 


>   I'm also unclear about what you mean by birds having dry mouths. 
Sure, there are birds with extensive rhamphotheca (such as parrots, 
hornbills, >toucans, etc.) but is this what you mean? If so, it says 
nothing to the position of a sealed oral margin due to fleshy structures
 outside of the jaws >themselves. Of course, some birds (again, 
especially hornbills) have a gaped jaw at all times, but I do not know 
if this exposes the interior of the >oral cavity, and the highly moist 
environment of a tropical rainforest might compensate for this 
(extremely speculation!).


     No, I mean that the interior of their mouth, including their tongue, is 
surprisingly dry. My girlfriend works in a pet store so I've had plenty of 
opportunity to play around with an African Grey. Also, I'm hoping to buy a 
parrot soon and so I've spent some time speaking with an expert on them. One of 
the things I found interesting was that a wet mouth is actually a sign of 
illness. Of course you might argue that they can get away with it because many 
of them live in tropical environments, but there are also some that live in 
cool temperate climates as well. So while I don't think the majority of 
dinosaurs were running around with unsealed, dry mouths, this does show that it 
may not have been a problem for species living in non-arid environments. An 
overbite similar to what we see in many birds may have been sufficient for 
desert dwelling species. 

Simeon Koning    






   
  

----------------------------------------
> Date: Fri, 23 Sep 2011 19:15:37 -0600
> From: qi_leong@hotmail.com
> To: simkoning@msn.com; dinosaur@usc.edu
> Subject: RE: Making Lip of It
>
>
>   Large teeth with some form of "preservative covering" -- again, we're 
> dealing with an untested argument, where the _teeth themselves_ must be 
> preserved in some fashion, although as David has pointed out before, this is 
> not necessarily intuitively correct, as well elephant tusks -- occur in a 
> host of living animals where the teeth are so ridiculously large they might 
> seem to argue against "lips" as well, such as various rodents. And while some 
> rodents have exposure of the distal tips of their incisors, this is very 
> minimal in general. The issue is, still, about what quality needs to be 
> preserved here, and how. With teeth, does the enamel itself need to be 
> protected, or can their be other methods, such as increased water intake, 
> that can allow this?
>
>   I'm also unclear about what you mean by birds having dry mouths. Sure, 
> there are birds with extensive rhamphotheca (such as parrots, hornbills, 
> toucans, etc.) but is this what you mean? If so, it says nothing to the 
> position of a sealed oral margin due to fleshy structures outside of the jaws 
> themselves. Of course, some birds (again, especially hornbills) have a gaped 
> jaw at all times, but I do not know if this exposes the interior of the oral 
> cavity, and the highly moist environment of a tropical rainforest might 
> compensate for this (extremely speculation!).
>
> Cheers,
>
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
> Backs)
>
>
> ----------------------------------------
> > From: simkoning@msn.com
> > To: qi_leong@hotmail.com; dinosaur@usc.edu
> > Subject: RE: Making Lip of It
> > Date: Fri, 23 Sep 2011 21:03:37 -0400
> >
> >
> >
> >
> > That's actually what I was suggesting (not very clearly I admit) with 
> > "stage 3. reduced lips with an overbite". I imagine there was probably a 
> > 'transitional' point between lizard lips and croc like jaws. Perhaps it 
> > started with some of the larger teeth protruding past the lips like the 
> > 'saber teeth' of some mammals. Maybe this trend continued until the lips 
> > were no longer needed as a seal due to an overbite. At this point, having 
> > fleshy, injury prone lips hanging over rather large, very hard teeth may 
> > have become a liability rather than an advantage, and so they were rapidly 
> > lost. This is easy to understand as I'm sure many of use have been punched 
> > or hit in the mouth and received a bloody lip as a result. Now imagine if 
> > you had a mouth full of serrated knives like this guy > 
> > http://www.dinosaur-world.com/weird_dinosaurs/species/dilophosaurus_wertherelli.gif
> >
> >
> >
> > Regarding pterosaurs: even some of the most basal pterosaurs had gharial 
> > like teeth, while many of the most derived forms had no teeth at all:
> >
> > http://www.ucmp.berkeley.edu/diapsids/images/pteroheads.jpg
> >
> > http://en.wikipedia.org/wiki/File:Rhamph_DB.jpg
> >
> > Of all the extinct Archosaurian groups we have discussed so for, pterosaurs 
> > seem by far to have been the least likely to have flexible, lizard like 
> > lips. If for no other reason than that there is simply no place for them to 
> > go. Many of the more primitive pterosaurs seem to have had teeth rather 
> > like this guy: 
> > http://2.bp.blogspot.com/_GHnh3ILnSo4/TRHG8p50XxI/AAAAAAAAEHM/Ggpjv4V_cMs/s1600/Kaprosuchus%2Bsaharicus.jpg
> >  Hence the argument from phylogenetic bracketing.
> >
> >
> >
> > In summary:
> >
> > I do not find the argument regarding tooth dessication convincing.
> >
> > I do not find the 'dry mouth' argument convincing since we have modern 
> > dinosaurs with dry mouths.
> >
> > The presence of nutrient foramina does not help us much in determining 
> > whether or not they had lips.
> >
> > I suspect that a fleshy covering over large teeth mounted on a jaw that can 
> > seal itself with an overbite would be more trouble than not.
> >
> > Phylogenetic bracketing seems to suggest that the common ancestors of 
> > crocodylomorphs, dinosaurs, pterosaurs and possibly turtles were lipless. 
> > This could explain the archosaurian propensity to evolve toothless beaks.
> >
> > I know this is all speculation; it's just that if I want to draw these 
> > things then I need to pick one or the other ; ). To be quite honest I 
> > prefer the lipped look, but I learned a long time ago that reality doesn't 
> > really care about what I like or don't like. As much as I hate to admit it, 
> > I feel that the (very) limited evidence seems to point to most dinosaurs 
> > having creepy, nightmarish bird-croc faces.
> >
> > BTW do you have a Deviantart page Jaime?
> >
> > Sim Koning
> >
> >
> >
> > .
> >
> > ----------------------------------------
> > > Date: Fri, 23 Sep 2011 16:56:57 -0600
> > > From: qi_leong@hotmail.com
> > > To: simkoning@msn.com; dinosaur@usc.edu
> > > Subject: RE: Making Lip of It
> > >
> > >
> > > This is the question that cats invoke: Why, exactly, can't an animal be 
> > > partially lipped? Again, how do you tell if something does and does not 
> > > have lips, aside from some practicality of _covering the entire tooth_? 
> > > The last issue should be known to be largely irrelevant, as the elemental 
> > > problem here is that lips have yet to be shown to preserve or conceal 
> > > _teeth_.
> > >
> > > Cheers,
> > >
> > > Jaime A. Headden
> > > The Bite Stuff (site v2)
> > > http://qilong.wordpress.com/
> > >
> > > "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> > >
> > >
> > > "Ever since man first left his cave and met a stranger with a
> > > different language and a new way of looking at things, the human race
> > > has had a dream: to kill him, so we don't have to learn his language or
> > > his new way of looking at things." --- Zapp Brannigan (Beast With a 
> > > Billion Backs)
> > >
> > >
> > > ----------------------------------------
> > > > Date: Fri, 23 Sep 2011 11:05:56 -0400
> > > > From: simkoning@msn.com
> > > > To: martyniuk@gmail.com; dinosaur@usc.edu
> > > > Subject: RE: Making Lip of It
> > > >
> > > >
> > > > I think I'm comfortable saying that most (if not all) pterosaurus 
> > > > almost certainly did not have lips. A great many of them had very long 
> > > > interlocking teeth similar to those of a gharial. It seems that their 
> > > > length and/or angle of projection would definitely preclude the lips we 
> > > > see in lizards today. Then of course we have the more derived forms 
> > > > with no teeth at all. It seems improbable to me that they would go from 
> > > > a 'gharial-toothed' form with big fleshy lips to a bird like beak with 
> > > > no clear transition. I can think of a few more reasons, but for me at 
> > > > least, these two are enough.
> > > >
> > > > Sim
> > > >
> > > >
> > > > ----------------------------------------
> > > > > Date: Fri, 23 Sep 2011 08:28:14 -0400
> > > > > Subject: Re: Making Lip of It
> > > > > From: martyniuk@gmail.com
> > > > > To: simkoning@msn.com
> > > > > CC: dinosaur@usc.edu
> > > > >
> > > > > "Pterosaurs seem to have been a largely toothed but lipless group with
> > > > > some non-fishing inland forms"
> > > > >
> > > > > Again, is there any actual evidence for this assertion? AFAIK the
> > > > > evidence is just as equivocal for non-beaked pterosaurs as it is for
> > > > > non-beaked dinosaurs.
> > > > >
> > > > > Matt
> > > > >
> > > > > On Thu, Sep 22, 2011 at 10:23 PM, Sim Koning <simkoning@msn.com> 
> > > > > wrote:
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > To reiterate my point about pterosaurs: there were insectivorous 
> > > > > > and toothed inland species (some Istiodactylids) that probably 
> > > > > > weren't making a regular habit of dunking their heads into water. 
> > > > > > Even the species that were fishing would have been doing so in 
> > > > > > saltwater, something that tends to rapidly desiccate tissues. Plus 
> > > > > > I doubt they spent their *entire* day soaking their heads in sea 
> > > > > > water, as I'm sure they would have needed to roost at some point. 
> > > > > > Kaprosuchus was most likely a terrestrial croc with what was 
> > > > > > apparently a largely terrestrial ancestry, and it almost certainly 
> > > > > > didn't have lips. Then there are the numerous mammalian examples 
> > > > > > with exposed teeth despite the fact that they are not easily 
> > > > > > replaced. I really don't think tooth dessication was that much of a 
> > > > > > problem at all for most animals with exposed teeth. Nor is a dry 
> > > > > > mouth for that matter: parrots have very dry mouths as they spend 
> > > > > > most of the time with their mouths partly open, and they are 
> > > > > > *dinosaurs*. In fact, if a parrot has a wet tongue it is usually a 
> > > > > > sign of illness. I really see no barrier to a dinosaur evolving a 
> > > > > > largely dry mouth, or exposed teeth, or both.
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > What can phylogenetic bracketing tell us? If we look at terrestrial 
> > > > > > crocodylopmorphs such as Sebecus and Kaprosuchus, we see jaw 
> > > > > > morphology with interlocking teeth that would not have left much 
> > > > > > room for lizard like lips. Pterosaurs seem to have been a largely 
> > > > > > toothed but lipless group with some non-fishing inland forms. 
> > > > > > modern birds have beaks as did many dinosaurs, many of which seem 
> > > > > > to have evolved independently. Kaprosuchus seems to have had a 
> > > > > > keratinous 'bumper' of some sort on the tip of the snout. Perhaps 
> > > > > > this is how the typical archosaurian beak started out? I can see 
> > > > > > the advantage in having a hard covering on the parts of the the 
> > > > > > mouth that were most prone to abrasion and injury. All this 
> > > > > > suggests to me that 'liplessness' was the basal condition for most 
> > > > > > of Archosauria. Perhaps a lack of fleshy lips allowed for the 
> > > > > > rather large sharp teeth we see in so many predatory archosaurs. 
> > > > > > Lizard like lips may very well have been more trouble than they 
> > > > > > were worth for a great many archosaurs. This is something I have 
> > > > > > yet to see addressed. The assumption often seems to be that lips 
> > > > > > would have been beneficial for predatory archosaurs, and so no good 
> > > > > > reason can be found for why they would be lacking. If you look at 
> > > > > > the open mouth of a lizard such as Komodo dragon, you will notice 
> > > > > > that their teeth are not even visible despite their large size. If 
> > > > > > a dinosaur such as Deinonychus had lips of this sort, it would have 
> > > > > > looked toothless when it opened its mouth. The reality is that the 
> > > > > > sharp teeth of Varanids actually tend to lacerate the tissue 
> > > > > > surrounding them. I suspect that this would have been a problem for 
> > > > > > many theropods, not an advantage.
> > > > > >
> > > > > >
> > > > > > I suspect the typical pattern that independently lead to beaked 
> > > > > > jaws in so many archosaur lineages may have been something like 
> > > > > > this:
> > > > > >
> > > > > > 1. Lizard lips with interlocking teeth > 2. Lizard lips covering 
> > > > > > jaws with an overbite > 3. Reduced lips with an overbite > 4. No 
> > > > > > lips with exposed teeth (most of Archosauria) > 5. Exposed teeth 
> > > > > > with a hard scaly covering on the skull > 6. Teeth with a rostral 
> > > > > > 'proto-beak' > 7. A reduction in size and/or number of teeth > 8. A 
> > > > > > toothless beak.
> > > > > >
> > > > > >
> > > > > > Simeon Koning
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > >
> > >
> >
>