[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Making Lip of It
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
> > > >
> > > >
> > > >
> > > >
> > > >
> >
>