Color Banding in Dinosaur Teeth - Reason? + plesiosaur repro. -Replies

["LESLIE F NOE" <L.F.Noe@derby.ac.uk>]

Hi all,

I have come across a similar situation in some Jurassic pliosaur teeth
to those mentioned previously, vis:
 
==> a series of thin stacked white or yellowish-colored bands,
numbering from 2-6. These do not run lengthways on the tooth crown,
but rather each "wrap around" thus forming one continuous line. They
can be found near the base, tip, or middle- no consistent pattern.<==

Not so much colour banding, as raised circumfurential (I assume this
is what is meant by "wrap around" ) ridges. These are variably placed
on the enamelled tooth 'crown' (although I have never observed it on
the 'roots' to date), and may or may not interupt the ornamentation
pattern of enamel ridges running the length of the tooth. The ridges
may continue uninterrupted, be increased or decreased in number and
'stoutness' stop altogether or start anew beyond the "shoulder" (as I
have termed it).

My thoughts were that this was in response to a stressed environment
(internal or external). My thoughts:

(1) Poor diet (as already mentioned), or lack of essential dietry
components. This could suggest seasonality of food supply (and hence
possibily seasonality) or migration cycles between feeding grounds
etc.

(2) trauma induced by illness or injury, I'm not sure how much
evidence (if any) there is for palaeopathological effects specifically
on teeth. I know some mososaurs have been accused of getting the
'bends' from diving too deep/long, but this was based on caudal
vertebrae (if my memory serves me).

(3) Stress due to reproductive cycle - is there any evidence of
effects on teeth in extant reptiles whilst egg laying? Should this be
shown to be the case it MAY allow sexing of animals by their teeth (ie
if found this feature is found the teeth belong to females, not found
represents indeterminate sex),

I know most of this is unstabstantiated speculation, but you asked for
thoughts!

Re: Plesiosaur reproduction, a couple of thoughts,

I am convinced at least some of the Plesiosauria are live bearers. The
point about ichthyosaurs embryos being relatively common may be
because most come from a restricted number of localities (for instance
none known for certain in the Oxford Clay Formation, despite the large
number of finds), suggesting to me an environment where pregnant
females gathered - a 'birthing pool' for want of a better term, which
was returned to year on year, combined with exceptional conditions of
preservation.

As regards terminal claws on plesiosaur paddles, at least one specimen
I am aware of (a pliosaur, Simolestes, PETMG R296) shows claw like
extensions on its terminal phalanges. These terminal elements may
frequently be missing, even in well preserved specimens as they are
very small. Paddles ending in the traditional 'dumb-bell' shaped
phalanges are probably in a large measure incomplete. It is not clear
from this specimen however if these were fore or rear paddles.

One last thought - in turtles the egg laying females are generally
much smaller than the males, so maybe there was a sex-size variation
in the Plesiosauria too, if they were egg laying the females could
drag themselves onto land, the males were much larger and could not.
(And avoiding predators doesn't seem to work for turtles as some sea
birds seem to specialise in eating young turtles as they emerge, and
certain predators can smell out and devour the eggs - seems to have
worked for a long time though!)

Lez

Leslie Noe,
Centre of Environmental, Earth and Applied Science Research,
School of Environmental and Applied Sciences,
University of Derby,
Kedleston Road,
Derby, DE22 1GB,
England.

e-mail: L.F.Noe@derby.ac.uk