[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Pleurocoelus question



Ray,

> Tom (Lipka), you answered, referring to the question of whether the
>  star-shaped cross-section of pulp in sauropod teeth is unique to Astrodon
>  johnstoni:
>  
>  "It isn't and that was my point!"
>  
>      So , Tom, I ask you: How could you possibly know it isn't, since, as 
you
>  say (to your knowledge), those of other sauropods' teeth have not been
>  sectioned for comparison?

How else can I explains this?  All of the teeth in question begin as 
cylindrical pegs proximal to the gum and terminate distally, after recurving 
lingually,  to a point (which itself is star shaped if pristine but there are 
commonly wear facets that destroy this feature).  For all intents and 
purposes, they are identical in morphology and differ only in overall size 
which _may_ only indicate ontogenteic differences. Regardless, they have the  
_same_ structure. So how can they be different if sectioned? This is really 
comparing apples with apples. Take any variety of apple, section them all 
equally and you get the same basic cross section. Repeat this sectioning 
along another but still common axis, and you get the same structure! Size 
does not matter and in the case of apples, variety (to be analagous with 
genus or species) does not matter. This is the _general_ apple autapomorphy! 
Ditto for sauropod teeth!

No matter how you slice it, the section comes out the same.


>      And you ask concerning the suggestion by Steve and me that teeth of
>  other species of sauropod having teeth that look similar or identical
>  externally be sectioned for comparison of internal pulp cross-section with
>  the same in Astrodon johnstoni:
>  
>  "To what end? Externally the teeth are virtually identical thus internally,
>  if
>  the x-sections were made at the "exact" same points on all specimens in
>  question, you would still have the star-shaped x-section."

I have answered this now, twice as best I can Ray. I'm sorry if your not 
getting the point. Or, I'm missing your point?

If Astrodon has a (I don't remember what type of star shape) say, pentagonal 
star cross section for the sake of argument, and ALL of the teeth from the 
genera we discussed are identical in morphology, then cutting them would 
result in the _same_ pentagonal cross section, prseuming preservation and 
permineralization have introduced no ill effect.

>  
>      Sorry Tom, but that seems nonsequitir. Since, as you say, no cuts for
>  comparison have been made, how do you know the pulp sections, "...would
>  still have the star-shaped x-section" [as in Astrodon johnstoni]? What is
>  the source of your information that sauropod teeth which seem to look 
pretty
>  much the same externally (yet are from different species) have similarly
>  shaped pulp cross-section?  (Can you provide a reference?)

As I have said. _Personal observation_.   I stated something to the effect 
that if the teeth were all mixed together, the fact that they were virtually 
identical  would make it virtually impossible to distnguish which was which.
But don't take my word for it. Ask anyone else who have seen the specimens. 
Off hand, Ostrom (1970) alludes to the similarrity of the Montana specimens 
to Astrodon.

(I'm on a lunch break and have to scram, so if you want a direct quote, I'll 
do it tonight!)

>  
>      You then state:
>  
>  "And even if there were any statistically significant differences in star
>  morphology, I doubt
>  they would be taxonomically significant."
>  
>  You seem to be presuming that the cross-section would be star shaped. 


Again, see the above analogy.

 Well,
>  it very possibly would be, but I suspect you agree that in science we must
>  take nothing on faith.  Yet, without faith, how can we accept your 
inference
>  as correct, in absence of experimental documentation?  

I'm not asking you or anyone to accept anything on faith. Skepticism is 
healthy in science. Experiment away my friend. I for one will not submit as 
single "astrodon" tooth for sectioning as they are far to rare for such a 
destructive process. Hence my suggestion of a non-intrusive method.


I think it more
>  scientifically appropriate to first determine whether pulp cross sectional
>  differences exist, then to determine the degree and nature of any 
variation,
>  and only then try to evaluate the possible significance, if any exists.
>  

All right Ray, say some differences  exist. So what? Please interpret this 
hypothetical data and how it helps taxonomy? Without a determinable owner 
known, it tells nothing. You still cannot give it a valid name!


>  You further say:
>  
>  "It sheds no new information as to the owner of the teeth."
>  
>      How do you know this before sectioning appropriate teeth?  Wouldn't it
>  at least tell us whether the 'owner' had a pulp cross-section like that 
seen
>  in teeth of Astrodon johnstoni?
>  

This is going in circles.... ;-)

>      And you feel:
>  
>      "Way to many to destroy (and way to few available) in the latter case.
>  We NEED
>  diagnostic bones and associated rami with teeth still in them!"
>  
>      Neither Steve nor I suggested destroying any teeth. Neatly cutting a
>  cros-section does not destroy, 

That is a matter of opinion. Once sections scrap material not whole complete 
(and rare) specimens! Cutting into anything is by definition, destroying it.


but it would add to our knowledge.

Doubtful in this case.

>  Furthermore, I did not suggest removing teeth from the bone, but would
>  advocate analizing teeth that are found seperated from the bone.

I never suggested this either. The implication of that remark was  that a jaw 
bone with teeth and associated skeletal material would likely have many 
diagnostic traits with which to elucidate taxonomic affinities.

>  
>      And, you quoted me a <snip>

>  "I am not aware of any."
>  
>      All the more reason to section some.
>  
>      You then said:
>  
>  "There are not that many teeth from all localities to (IMHO) conduct a
>  meaningful study..."
>  
>      Go to the one of the bigger fossil shows and see the shameful number of
>  sauropod teeth for sale from the U.S.A. and from various places around the
>  world.

Shameful is in understatement! Fossil shows are the LAST place to obtain 
specimens. If they have not beeen properly catalogued and accessioned into a 
valid repository (museums, etc.) than they are useless and most journals will 
not publish "results" from material procured in this manner. Furthermore, it 
is highly unlikely that any respectible funding institution (NSF etc.) would 
willingly fund someone to go to a fossil show to BUY such fossils for such a 
study. This is a moot point!
  

>      I'm unsure whether CT scans would clearly show the pulp pattern as
>  distinct from, say, the dentine or the enamel,  

Hence my stated uncertainty.

but, if it would, one could
>  scan a whole bunch of teeth simultaneously (if properly arrayed for the
>  scan).  

This had crossed my mind.


It should not be expensive, either, because there are probably
>  numerous institutions who would probably donate that service.  I know one
>  locally that would definitely do it without charge, because they have twive
>  done free CT scans on dinosaur materials for me.


That's all well and good but I don't, at present, have access to any of the 
teeth we've been discussion except for my Arundel material. We would still 
need to acquire a representative sampl of sauopod teeth from all the places 
in question and from their respective repositories. It is indeed a sizeable 
project to conduct but to me, there appears  (again I say _at_present_) 
little justification  for it.

Lunch is over so I'll end here. 

Hastily,

Tom

Thomas R. Lipka
Paleontological/Geological Studies
Tompaleo@aol.com