Re: polyphyodonty in dinosaurs

[NJPharris@aol.com]

I am far from an expert on dinosaur dentition, but here goes...

In a message dated 10/19/00 11:18:26 PM Eastern Daylight Time, 
kinman@hotmail.com writes:

>      As an on-topic spin on the former discussion, I would assume that 
>  dinosaurs, most other reptiles, and non-amniotes, all are polyphyodont 
>  (multiple-to-continuous tooth replacements)

Yes, in all known cases.


>  and also homodont (all teeth 
>  generally of similar shape, usually more conical than flat).  

Coelophysoids, compsognathids, spinosauroids, _Ornitholestes_, tyrannosaurs, 
probably some other theropod groups I'm not thinking of, heterodontosaurs 
(obviously), pachycephalosaurs, basal ceratopians, and basal ornithopods all 
exhibit more or less marked heterodonty.  I believe in all of these cases the 
premaxillary (and anterior dentary, if present) teeth are different in form 
from the maxillary (and posterior dentary) teeth.  Ceratopids and 
iguanodontian ornithopods could be said to have reverted to heterodonty when 
they lost their premaxillary teeth.


>  Therefore the 
>  wisdom-tooth problem would occur rarely, if ever, in something like 
>  dinosaurs (or any other non-mammal).

Indeed, dinosaur tooth counts can vary considerably even within species (and 
sometimes even between the left and right jaws of individuals).


>       An on-topic and interesting question would be whether plant-eating 
>  dinosaurs ever develop heterodont teeth with mammal-like "molars" for 
>  grinding.

Hadrosaur and iguanodont teeth could be said to be molar-like, in that they 
are more or less flat and display complex enamel patterns.  But advanced 
ornithopods managed to evolve effective grinding teeth while retaining the 
polyphyodont condition.  Also, the method of getting the tooth surfaces to 
rub against one another is different in ornithopods (pleurokinesis) from that 
in mammals (moving the jaw back and forth or side to side).


>  If they do, I assume they do not develop the same precise kind of 
>  occlusion, since dinosaur identification is rarely, if ever, based on 
dental 
>  characteristics (or am I wrong on that?).

All too often.  Check out the sad history of such names as _Deinodon_, 
_Trachodon_, _Troodon_, _Aublysodon_, _Szechuanosaurus_, and many others.

--Nick Pharris, who has (knock on wood) twelve fully functioning molars :-B