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RE: Making Lip of It



I appreciate the long, extended reply from Sim Koning to my post on my blog. 
Unfortunately, many of the issues of equivocality Sim mentions are problems 
that continue to elude solution (as yet unpresented, anyways). There are 
solutions to some of these issues, and I've been somewhat hesitant to affirm 
what I can or tried to deduce on my own study, which has been limited to visual 
examination and some induction from the literature.

  The short of it is that there is no catchall method that tells us that 
clustering foramina at the front of the jaws do or do not refer to lips. They 
are exits for nerves and blood vessels, regardless of whether a beak, a lip, or 
closely adhering cornified "croc lips" are preserved. As I noted, several 
problems of correlating flesh to bone requires understanding the relationship 
and the variability of the types of tissues involved, which cannot be simply 
solved by looking at a skull. We have to make external inferences to form 
hypotheses, as David noted (and well) in regards to the nature of exposed teeth 
and gum tissue. Extant crocodilians can get away with lips, so it is said, 
because they are on average very very wet. Terrestrial animals have fewer 
options to keep their mouth wet, and these tissues, and the internal oral 
cavity, can become dried out and increase evaporation of body water, which is a 
real problem.

  My quick observation on the "beaks" in the Paulian sense was built on an 
inference from phylogenetic reasoning and the lack of any comparable analogue 
from which to reliably deduce the hypothesis. Paul's argument, that the beak is 
a remnant of a proto-avian beaky margin, is made solely on the basis of 
ancestry with *Archaeopteryx lithographica* and their being the sister taxon to 
birds, but it has never been demonstrated where basal birds gained a beak of 
any sort, and with basal *Avialae* included several toothed taxa, it seems 
plausible such a structure hadn't developed.

  This was not to be the last bit on the topic, as I was going to make some 
comments on the issue of teeth, lips, and beaks in regards to ornithischians, 
crocs, etc., which seem to preserve both morphologies and sometimes in the same 
jaw. So I kept several comments brief. I included, for example, a 
reconstruction of the snout of *Velociraptor mongoliensis* in ventral view in 
which I constrained the available space between upper teeth and lower jaw, 
which leaves limited space for ligament, flesh, labial squamation, and a beak. 
How much room, then, is possible or necessary for all tissue of relevance? 
That's a question I have no answer for right now.

  The presence of the overbite was also peculiar, and I thank Sim for 
mentioning this, because it's an interesting problem that feeds into the 
response by David as a useful excuse for an exercise in a topic of limited 
argument: nonorthal jaw movement. In this case, most lacertilians have a 
streptostylic quadrate, which permits a great deal of propalinal motion, and 
can increase and decrease an overbite. While this is not present in some taxa, 
and certainly no dinosaur, it may be said that dislocation (partial) is 
possible in some taxa, but this allows such minimal stylic movement that such 
mobility is irrelevant save on a kinetic transfer system. Some crocs, however, 
as in some dinosaurs and many, many birds can actively reposition their 
mandible regardless of the position of the quadrate due to lack of a posterior 
walk for the mandibular cotylus; in mammals, as in turtles, relative 
dislocation on one of these joints allows translational movement, or 
malocclusion of the jaw margins, for temporary mechanical advantage (we can 
enjoy this with side-specific crushing and chewing, cats and dogs use it to 
take advantage of their carnassial molars, etc.). This has been used to explain 
peculiar wear in the jaws of some dinosaurs (e.g., ankylosaurs). 

  All of this is particularly fascinating, and have their fingers in the 
subject of what kind of tissues surround the jaw. They are all relative, and 
many different related groups can have different morphologies and complexes of 
tissues (e.g., *Pelecanimimus* and *Bonitasaura* have both been argued to have 
a rhamphothecal "edge" posterior to the jaw margin in either the upper or lower 
jaw, relatively), while ornithischians are said to have a rostral beak, some 
basal ornithischians have rostral teeth that appears to oppose a mandibular 
beak. The issue, then is whether a beak can or should exist where there are 
teeth in the same position (Paul's argument), and how you can discriminate this 
from either just teeth and cornified skin, teeth and lips, not teeth or beak, 
or a beak alone, without having to know whether there are teeth to begin with.

  We're not there yet.

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: Wed, 21 Sep 2011 22:12:13 -0400
> From: simkoning@msn.com
> To: qi_leong@hotmail.com; dinosaur@usc.edu
> Subject: RE: Making Lip of It
>
>
>
> Jaime,
>
>
>
>      I'm glad you posted this article. My girlfriend is a science
> illustrator and she has been motivating me to start drawing with more
> frequency. I've started drawing dinosaurs again, but I've
> been growing frustrated with this lip issue. It's not exactly a small
> problem, as it has a dramatic effect on the way a dinosaur looks. I've read
> through your article a few times and I have some things I'm hoping to
> discuss with people more knowledgeable than myself.
>
>
>      In your article you state that the placement of the foramina seem to 
> indicate lizard-like tendenous 'lips' similar to those found on lizards. I 
> often found this somewhat convincing in the past, but after spending the last 
> few days looking at dozens of pictures of crocodilian and squamate skulls, 
> while at the same time reading arguments from others on this list, I'm 
> leaning more and more to the lipless side of this debate. Though I do have 
> problems with some of the arguments being put forward by both sides. For 
> example, in old post on this list Tracy Ford argues that the presence of an 
> overbite strongly suggests a lipless morphology, since lizards tend to have 
> interlocking teeth and no overbite. However, from what I can tell, geckos 
> have an overbite rather similar to that of some dinosaurs.
>
> http://digimorph.org/library/pop.htm?/specimens/Gekko_gecko//specimenlarge.jpg
>
> Now on the other hand, so do some crocodilians. So, I don't find the presence 
> or lack of an overbite very convincing either way. What it does suggest, to 
> me at least, is that they would have been able to at least partially seal 
> their mouths without the aid of lips.
>
>      Arguments that revolve around foramina don't seem to help much. If they 
> are diagnostic of anything, it seems to be degrees of sensitivity and 
> vascularity of the skin around the jaws. The nutrient foramina found around 
> the jaws of spinosaurids follow a single channel until they reach the tip of 
> the snout, where they begin spread out or form several rows. This suggests to 
> me that the foramina had more to do with sensitivity of the mouth than to the 
> presence of lips. Deinonychus has a double row of foramina on the maxilla 
> while they seem (to me) to be lacking on the rostrum. So perhaps they lacked 
> lips altogether and possessed a keritanous proto-beak? I know you do not like 
> this idea, but splitting the lip tendon/ligament seems only to be a problem 
> if you assume they had lips in the first place.
>
> http://digimorph.org/library/pop.htm?/specimens/Osteolaemus_tetraspis//specimenlarge.jpg
>
>     If you look at the jaws of a dwarf crocodile, you will notice that they 
> are practically covered in foramina. I know some have argued that the 
> liplessness of crocs is probably due to their aquatic nature, but then I have 
> to ask why this did not present a problem for terrestrial crocs such as 
> Kaprosuchus or Simosuchus, both of which were fully terrestrial, with one 
> likely an herbivore.
>
> http://en.wikipedia.org/wiki/File:Simosuchus_clarki_skull.jpg
>
>     In the case of Simosuchus, the placement of foramina does not seem to 
> differ greatly from what we see in some dinosaurs such as Deinonychus. You 
> may notice that there is a cluster of foramen located on the maxilla, while 
> they are lacking on the rostrum. Perhaps the tip of the snout was covered 
> with a hard keritanous covering, perhaps a sort of proto-beak? This leads me 
> to my next point: I suspect that most, if not all ornithodiran archosaurs 
> were 'lipless' and this may have been why so many lineages tended to evolve a 
> beak of one form or another. Maybe a lipless mouth is a necessary precursor 
> to a beak. I suspect that a beak may have often started out has a hard 
> covering on the snout that gradually worked its way back along the jaws, 
> replacing the teeth in the process. But as you point out, a beak of this 
> nature may not have been able to coexist with lizard like lips. This seems to 
> present an argument against dinosaurs having lips since we know that many 
> archosaur lineages evolved beaks independently..
>
>
>     So, when I consider these points, I am inclined to depict most, if not 
> all dinosaurs without lizard like lips and I suspect the beaked, lipless 
> depictions of dromaeosaurids is the most probable. Of course, I am by no 
> means an expert on this subject, but since there is so much disagreement, I 
> am forced to pick one option or the other unless I intend to draw them with 
> blank mouths.
>
> Simeon Koning.
>
>
>
>
> ----------------------------------------
> > Date: Sun, 18 Sep 2011 02:19:13 -0600
> > From: qi_leong@hotmail.com
> > To: dinosaur@usc.edu; Vert.Paleo.Mailing.List@listproc.usc.edu
> > Subject: Making Lip of It
> >
> >
> > I'm going out on a limb and posting my (sometimes) controversial opinion in 
> > regards to that perennial problem of dinosaur lips. In this, I will 
> > temporarily gush over Larry Witmer's biology work while at the same time 
> > taking an aim at a cherished childhood icon, "Crash" McCreery's 
> > "velociraptors" from _Jurassic Park_. The conclusions are anything but, but 
> > I had a lot of fun making the art. Check it out at my blog, or follow the 
> > direct link: http://qilong.wordpress.com/2011/09/18/making-lip-of-it/ . At 
> > over 3,500 words, it's my largest single piece written exclusively online, 
> > and represents the culmination of a few lines of data regarding jaw 
> > structure and soft-tissue analogies. As I state in the post, I'm an amateur 
> > and would appreciate positive criticism.
> >
> > 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)
> >
>