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Re: recapitulation



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.