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Re: recapitulation




On Thu, 22 Jan 1998, Dinogeorge wrote:

> In a message dated 98-01-22 07:26:55 EST, zooamy@zoo.latrobe.edu.au writes:
> 
> << The juvenile skulls of Velociraptor bear distinctive
>  teeth, they are unserrated and have a constricted base, whereas those of
>  adults are typical blade-like serrated theropod teeth. Now if ontogeny was
>  recapitulating phylogeny we would have to assume that the unserrated tooth
>  with constricted base was the ancestral condition. By outgroup comparison
>  we can see that the adult tooth morphology is the ancestral one.  >>
> 
> In the BCF phylogeny, this is not necessarily the case. The ancestral tooth
> morphology--going all the way back to the common ancestor of Dinosauria--could
> well be the unserrated teeth with constricted base that are found in the
> smallest theropods and birds, from which would be individually derived the
> great variety of large, serrated theropod teeth. There is really no such thing
> as a "typical" theropod tooth; the teeth are quite distinctive among the major
> theropod groups. Large theropod teeth are usually serrated, but the serration
> patterns and shapes are distinctive and >all<  might well be derived
> independently of one another from the simple, unserrated ancestral form.
> 
The point is well taken that there exists variety amongst the large so
called "typical" theropod teeth.  Nevertheless I don't see any evidence
that all are derived independantly from an unserrated ancestor. I don't
know if there is any evidence for unserrated maxillary and dentary teeth
in any sized theropod outside the Maniraptoriformes (premaxillary teeth
seem to be a different story). What we really need are some more
ontogenetic series. The only good one I could find in the literature was
that of Rio... er sorry, Coelophysis. Very small specimens of this appear
to have teeth just like those of the adult, no basal constriction here.
Unfortuneately I couldn't find any word in Colbert's description on wether
the really tiny individuals had serrations on their max teeth or not. 

cheers
Adam Yates