Re: Theropod phylogenies

["Tim Williams" <twilliams_alpha@hotmail.com>]

"Richard Forrest" <richard@plesiosaur.com> wrote:


> If phylogenies based on the morphological analysis of the skeletons of
> modern birds are so unreliable, surely the same must be true of cladistic 
> analyses of theropod dinosaurs,

A quick answer...

I would disagree.  The biggest obstacle to resolving the interrelationships 
of modern birds is their fossil record: It's utterly dreadful.  This is 
especially the case when it comes to the basal representatives of modern 
avian orders.

> especially if they are so closely related to
> modern birds that some contributors to this site make no distinction?

Many folks (myself included) are convinced that birds are a subset of 
theropod dinosaurs.  Nevertheless, we still make a distinction between birds 
and non-avian theropods.  Similarly, the contention that bats are flying 
mammals still allows us to delineate between bats and non-chiropteran 
mammals.

> And if this is the case, don't we need to treat these cladograms as rather 
> tentative hypotheses rather than solid phylogenies?

Unless the Almighty tells us how individual lineages evolved, we are never 
going to KNOW what happened.  Whatever your method of choice is for 
resolving relationships - fossil data, molecular data, pure intuition, or 
combination of these - you can never be certain of how evolution occurred.  
All we can do is see how each hypothesis stacks up against the available 
evidence.  In this respect, I think the birds-are-dinosaurs hypothesis is 
looking pretty darned good.



Tim

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