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Re: recapitulation




On Fri, 23 Jan 1998, Dinogeorge wrote:

> In a message dated 98-01-23 01:57:00 EST, zooamy@zoo.latrobe.edu.au writes:
> 
> << 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.>>
> 
> There are enough differences among the teeth of the different groups to render
> the hypothesis of a common origin for serrated theropod teeth questionable. In
> this, I see more evidence against the common-origin hypothesis than for it.

The different styles of teeth could be modifications of a serrated
ancestor just as easily as they could of an unserrated ancestor.
 
> 
> Speaking of unserrated teeth, I'm pretty sure the small theropod
> _Archaeornithoides deinosauriscus_ had such. Also, I recall a paper by
> Whetstone & Martin that favorably compares _Archaeopteryx_ and croc
> teeth--putting unserrated teeth with constricted bases into an unquestioned
> outgroup of dinosaurs and birds and thus at least raising the possibility that
> the common ancestor of crocs, dinos, and birds had unserrated teeth with
> constricted bases. Martin in particular published photos showing considerable
> similarity in detail between croc and _Archaeopteryx_ teeth.
> 
Archaeornithoides is of uncertain phylogenetic position, it could well be
a maniraptoran, in which case it is not damaging to my line of argument. 
Yes there is the possibility that the avian style tooth is ancestral for
Archosauria. However given that amongst the pseudosuchia it is only found
amongst the crocodylomorphs and not in the stem groups leading to this
clade (ornithosuchids, phytosaurs, aetosaurs, prestosuchids, rauisuchids,
poposaurids etc.) it is simpler to assume that the character evolved twice
once in the crocs and once in the coelurosaurs. 

Cheers

Adam Yates