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




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