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Re: A load of questions



From: Mike Hoffmann <Mike.Hoffmann@mch.sni.de>
 > 
 > - Whatever happened to Stegosaurus' "second brain"?
 > 
 >      I recall that when I was a kid, there was this notion of stegosaurus
 >      having such a small brain that it needed some extra nerval support
 >      in its spine to move the hindlegs. While I understand that such an
 >      old notion may be silly today, I wonder why it is that you don't even
 >      read about it anymore, along the lines of "theories that didn't make 
 > it".

That was just a cute way of saying that its sacral ganglion was
larger than its brain.  This is as true now as it was when you
were young.  It is just that modern kids books are not quite so
condescending, and are not quite so cutesy.

So, the accurate statement of the facts hasn't changed - it
is not a failed theory - it is just that the old *in*accurate
way of describing it is no longer used, even in kid's books.
A sacral ganglion is not a second brain, even if it *is* larger
than the brain.

[Note, the sacral ganglion is larger than the brain in many,
or most, sauropods as well as in stegosaurs].
 > 
 > - Protoavis and birds=dinosaurs, dinosaurs->birds or dinosaurs!=birds
 > 
 >      Is there any up-to-date information and newest theories on the
 >      significance of Protoavis and what it means for the relationships
 >      and evolution of reptiles, birds and dinosaurs? The "latest" information
 >      I have available is from Don Lessems "Dinosaurs Rediscovered", which,
 >      although the book isn't that old, the information in it, concerning
 >      the findings and theories of whats-his-name Chatterjee(sp?) is from
 >      1989-1991.

Not really.  Chatterjee's finds are still being digested by the
scientific community, so there are no firm conclusions yet.

Actually, rather little has been published since the first wave
of responses after his publication of the description.

With few exceptions, almost all are very skeptical of his
identification of this animal as a bird, but as far as I
know a detailed rebuttal has not yet been published (at least
I have not seen one, or a reference to one).

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).

Actually, even that possiblity is hardly strongly supported,
as the specimens were badly crushed, and much of his 'data'
takes the form of reconstructions of the uncrushed state.
This is subject to error, and needs to be verified by other
workers.  One little piece of the animal that wasn't too
badly crushed looks to *me* like the ankle of a Ceratosaurian
theropod dinosaur!

Now, given Chatterjee's poor track record in identifying
the evolutionary relationships of the organisms he studies,
I think it is extremely unlikely he is right on this one.
[He once proposed that the tyrannosaurs had a seperate origin
from other dinosaurs - being descended from the Triassic
Poposaurus, while other dinosaurs were descended from another
branch of the thecodonts].

 >      Have his results been confirmed and has the whole theory of birds
 >      being either descendants or even birds *being* dinosaurs, been revised?

The "birds are dinosaurs" thing is the *same* as the birds are
descended from dinosaurs model.  The reason for the treatment is
that there is a school of taxonomy that insists that *all* descendants
of a the most recent common ancestor be included in any taxon. Thus,
by this rule, the Dinosauria must include *all* descendents of the
first dinosaurs no matter how changed.  Therefore, *if* the birds
are descended from dinosaurs they *are* dinosaurs.

Now, I do not hold to this school of taxonomy  (you may have
seen my debates on the acceptablility of "paraphyletic" taxa
- that is on whether taxa that do *not* include all descendents
are valid).  Thus, to me it does not follow that being descended
from dinosaurs makes a bird a dinosaur.

Dr. Chatterjee is proposing that Protoavis proves that birds
are descended from the early cursorial crocodilians. Dr. Martin
has long held this position for other reasons, and is the only
other paleontologist I know of that accepts Dr. Chatterjee's
identification of Protoavis as a bird.

Now, *if* Dr. Chatterjee is right (fat chance), then the cladistic
school of taxonomy would require that birds be classified as
crocodiles!

[Actually, this points out one advantage of accepting paraphyletic
taxa - this allows one to separate the birds as an independent taxon,
and *leave* that classification unchanged even if the opinion about
the ancestry of the group changes].

 >      Have there been newer findings on Protoavis?

No.

 > *Is* there in fact such
 >      a creature or was it just a case of multiple dinosaurs having been
 >      erroneously put together as one animal?

No - it is one animal, just a very badly damaged one.
[Actually, Dr. Chatterjee found the remains of *two*
individuals - but both were very crushed].
 > 
 > - What is a Utahraptor?

It is a large relative of Velociraptor that was recently
discovered in Utah.  That it happens to about the size of the
oversized Velociraptors of JP is just a coincidence.

 >      I haven't been able to find *anything* on that beast, except for a
 >      bit of responded-to mail on the Compuserve Dino Forum.

It is too new, it was only discovered last year.
It takes quite a while for a skeleton of that size
to be excavated, prepared, and studied.  It takes even
longer for much real data to get into the popular literature.
[A *preliminary* description has already been published in the
technical literature, but that is hardly what you want; it
was also mentioned in the Dinosaur Society newsletter a few
months ago].

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.
 > 
 > - What is the latest theory on dinosaur beginnings?
 > 
 >      The "recent" info I have is that the Herrerasaurids and Staurikosaurids
 >      are the earliest dinosaurs and may have been the forbears from which
 >      the Saurischians and Ornitischians branched off.

Close.  The best evidence right now is that the herrerasaurs
(including the Staurikosaurids) were (just barely) on the
line to the Theropods, and thus slightly past the common ancestor.
[That is, they have derived features otherwise only found in
theropods dinosaurs, and not in any other group of dinosaurs].

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).

The common ancestor may not have been quite so cursorial
(adapted to fast running) as the known herrerasaurs, but otherwise
was probably very similar to the staurikosaurids.
 > 
 >      Is that still considered gospel? Is SOuth America to dinosaurs what
 >      East Africa is to the evolution of man?

Probably.  Certainly the oldest currently known members of each
of the main lineages come from there.
 > 
 > - Where do I get more, more, more information that is up to date?
 > 
 >      I just leave that question in. I hope to join the Dinosaur Society
 >      soon and look forward to their newletters that will hopefully have
 >      answers to lots of my other questions.

That is one very good source for staying up to date.

[Hmm, I haven't gotten a newsletter in some time - are they just
late, or has my membership run out on me?]

 > Some of the discussions in here are a bit beyond me, but I prefer that to the
 > sadly a bit over-simplistic discussions on Compuserve - which are as often as
 > not "infiltrated" by creationists.

If you have any questions about terminology or significance,
ask, and I will try to clear the matter up.

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

The peace of God be with you.