Re: Juravenator; or How not to perform a phylogenetic analysis

[Tim Williams <twilliams_alpha@hotmail.com>]

Tom Holtz wrote:

> > Not every paleo paper needs to have an accompanyiang cladogram.
>
> However, the significance of this specimen (outside those researchers who
> are simply interested in theropod anatomy) lies within its phylogenetic
> context.

I'll second that.  If you're going to propose a phylogenetic hypothesis, 
then you need to do a phylogenetic analysis.  At the moment, cladistics is 
the only game in town.  I know many scientists (and non-scientists) gripe 
about this method, especially how accurate or "correct" it might be (or 
might not be); but I've yet to see a more objective or comprehensive way of 
evaluating relationships among taxa.  (Perhaps more pragmatically, that's 
the same attitude of most journal editors and reviewers.)  To put my own 
spin on what Mickey said, the selective *ad hoc* culling of taxa is a 
totally separate issue from whether or not a cladistic analysis is 
beneficial to a paper.

> For example, if it were found to be a basal tetanurine, there
> would be no particular suprise if its body was entirely covered with
> scales (NOTE: we have no reason to suspect that of Juravenator: only
> limited patches are known).

I have a feeling that the distribution of feathers versus scales in 
coelurosaurs may reflect the capricious nature of preservation more than 
anything else.  For example, we have the "inside-out" hatchling _Scipionyx_ 
with its innards preserved, but no sign of integument - the hindlimbs (at 
least) should have been scaly in life, since even birds have scaly feet.  On 
the other hand, most Liaoning theropods (avian and non-avian) that have at 
least part of the integument preserved have no trace of the internal soft 
anatomy.  And as Norell said, the various _Archaeopteryx_ specimens vary 
greatly in the way the plumage is preserved.

Rather than re-writing the evolution of feathers in theropods, I think the 
simpler explanation might be just to blame those bloody microbes.  
Decomposition is a very complicated business, involving an interplay of 
biological, chemical and physical factors.  Minor changes in the chemistry 
of an environment can have profound effects on the microbial populations 
lurking inside.  Sometimes the inside of the body decays faster than the 
outside, other times the opposite is true; and when the outside of the body 
survives long enough to be preserved, different types of integument show 
differential preservation.

Cheers

Tim