[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: A load of questions

From: Mike Hoffmann <Mike.Hoffmann@mch.sni.de>
 > I wrote:
 > > I *have* read the first half of Chatterjee's paper, and I am
 > > less than convinced.  Most of the evidence he adduces for
 > > Protoavis being a bird could equally well indicate it is a
 > > primitive terrestrial crocodilian  (the earliest crocodilians
 > > were terrestrial runners, not aquatic hunters).
 > I gather that, except for that specialist on bird fossils (L. Martin?) there
 > has been no peer review of the findings?

Well, technically it was peer-reviewed, in that it was published
in a peer-reviewed journal.  But there has been little *detailed*
scrutiny of the paper.
 > [in another response mail, someone said that Ostrom has done a short one]

Yep, and Ostrom's point about the crushed state is well taken.
The specimens looked like they had been through a meat grinder.
 > > workers.  One little piece of the animal that wasn't too
 > > badly crushed looks to *me* like the ankle of a Ceratosaurian
 > > theropod dinosaur!
 > You have seen the finds themselves? Or photos of it?

Drawings and photos.  I have a photocopy of the main paper
by Chatterjee.   Unless you know some comparative anatomy,
most of that paper will be rather incomprehensible, but it
does include drawing of all of the little bits and pieces,
and photographs of the specimens prior to removal from the 

If you have access to a good university library, I could give
you the citation for the paper so you can get it yourself.
[It is quite long - it is one entire issue of the journal].
 > > Now, given Chatterjee's poor track record in identifying
 > > the evolutionary relationships of the organisms he studies,
 > This sounds like Chatterjee is only good at finding fossils, but he should 
 > then immediately deliver them up for interpretation before he himself has a
 > go at it. :-)

That is certainly my opinion.  I suspect that some paleontologsts
ageee with me, but there are certain courtesies in the professional
journals that discourage saying such things in print.
 > > are valid).  Thus, to me it does not follow that being descended
 > > from dinosaurs makes a bird a dinosaur.
 > The uncertainty of the experts. I wonder if I should just become a 
 > creationist
 > and live in complete, if narrow-minded security. It may be a lot easier.

Well, this disagreement is not about anything of real "substance".
It is more of a disagreement about the format one should use in
summarizing the agreed upon facts.

A classification following the cladistic prescriptions and one
following the less strict rules of the evolutionary taxonomist
school usually represent essentially the *same* actual phylogeny.

The thing to keep in mind is that, to some extent all higher
taxonomic groups (above species) are human artifacts - constructs.
There is *always* an arbitrary component to classification,
though cladists like to pretend their methods eliminate arbitrariness.
[Actually, the cladistic methods just disguise the arbitrariness].
 > > It is likely to be in Donald Glut's new book when it comes
 > > out next year, but I doubt you will see much before that.
 > I can't wait.. the idea of 1200+ pages on mesozoic life makes me slobber on
 > my keyboard.

Same here - I was disappointed no end to discover it has been
delayed until February.
 > > However, the actual common ancestor probably differed only in
 > > a few relatively inconspicuous ways, since the derived features
 > > in question are all very subtle (position and size of various
 > > bony processes and the like).
 > I understand that to mean that there is *no* and probably wasn't a true 
 > "first"
 > dinosaur. Sort of like there was no "missing link" in human evolution. Finds
 > will just show more or less reptilian vs. dinosaurian features, but nowhere
 > to draw the line. Am I wrong?

This is not an easy question to answer.  Certainly no currently
known fossil is clearly the common ancestor. Furthermore, the
common ancestor *is* likely to be intermediate in many ways.

Now, cladistic methods purport to be able to reconstruct the
common ancestor.  And to some degree this is true, but the
usual way the method is applied does not allow for intra-
specific variation in diagnostic characters, so it is likely
to make errors of details when applied at this low a level.

Also, it is not clear that even if the common ancestor were
actually found, it would be recognised as such - for a variety
of reasons.

What is likely to have occured is a series of species with
prgressively more dinosaurian features.  The first species
in that series that had all of the diagnostic characters
of dinosaurs would count as the first species of dinosaur.
[Though I suspect that due to polymorphism, it may also have
had some derived features of particular lineages of dinosaurs
in at least some individuals].

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.