Re: Phylogenetic bracket question

[chris brochu <cbrochu@fmnh.org>]

As I see it, the phylogenetic bracket basically makes predictions more
than conclusions.  On phylogenetic grounds, we would predict skin
impressions for Deinonychus to show some sort of plumage -
dromaeosaurids are ultimately descended from an animal with feathers or
protofeathers or whatever, and at least one dromaeosaurid
(Sinornithosaurus) has them. I would still code Deinonychus with a "?"
for such structures, but would expect them should preserved skin be
found. 

Is secondary loss a possibility?  Sure - the phylogenetic bracket, in
the absence of other evidence, would reconstruct dolphins with fur and
tyrannosaurids with a complete third digit.  But without this other
evidence, secondary loss is a less parsimonious statement.  

The question to be asked at this point is, why would any nonavian
coelurosaur *not* have had feathers?  Some have argued that large-bodied
coelurosaurs (tyrannosaurids, etc.) might have lost them to shed heat,
but we don't know that they were absent.  Why would you *want* to
reconstruct Deinonychus without external dermal fibers?

chris

Larry Dunn wrote:
> 
> Well, I never thought I'd be asking this particular
> question, but, at this point, is it at all
> scientifically plausible to argue that _Deinonychus_
> did not have 'feathers"?
> 
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-- 
----------------------
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
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Chicago, IL 60605

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