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

RE: "Feathery fossil shows birds aren't dinosaurs"



> From: Ken Kinman [mailto:kinman@hotmail.com]
> Sent: Thursday, June 22, 2000 5:35 PM
>
>     Even if they are feathers, I am wondering what kind of logic
> they could
> possibly use to conclude that feathers did not evolve in dinosaurs.
>     I hope there is more to it than that, or I am going to be very
> disappointed in these guys.

Prepare to be disappointed, then...

(Okay, the rest of their logic is basically: a) coelurosaurs all occur after
early birds, which they don't; and b) birds must have evolved in trees, and
coelurosaurs couldn't live in trees (good thing they have a direct
Timeovision (tm) monitor to show that both these statements are true)).

Now, about _Longisquama_.  Despite George's impulsive outbursts (which I
will be charitable and say are due to his strong attachment to his own
hypothesis), the fact that I described _Longisquama_ as not being an
archosauromorph (much less a theropod!!!) has nothing to due with my
position on the origin of birds, and everything to do with the anatomy of
the critter itself.

In order to comment on the new paper in Science (see below), I was sent a
.jpg file of a closeup of the anterior end of the critter, as well as the
published photos.  (Please don't ask me for a copy, because I am not certain
if I would be allowed to send them out.  You might want to approach Jones or
Ruben if you could demonstrate you had the need for the photo, but PLEASE
don't everybody on the list swamp them with emails!!).

Okay, anyway, I finally had a real good view of the specimen. I had been
expecting something that could at least be a decent archosaur, maybe even an
ornithodiran.  I was wrong.

There are triangular chips in the rock and bone where the antorbital and
mandibular fenestra would be if present.  In the original paper Sharov
admits this, but later incarnations of the line drawings show these features
being present.  To be fair, we cannot say that these structures were absent
or present.  HOWEVER, this ain't Geol 104 (my non-majors dinosaurs class):
there are other characters to look out to determine if something is
archosaurian or archosauriform or archosauromorph.  Does _Longi._ have them?
Let's look...

Unfortunately the posterior end of the animal and the end of the forelimbs
aren't preserved: these contain a lot of important characters.  Furthermore,
the braincase isn't exactly accessible.  Additionally, the cervical ribs
aren't preserved (these are also very distinctive for archosauromorphs).
However, we can look at a few other features which are preserved.

Archosauriforms have theocodont dentition (remember back in the old days
when thecodont was a form of dentition...  Okay, maybe not...).
_Longisquama_ is described by Sharov as having acrodont dentition, found in
lots of primitive diapsids but NOT in archosauriforms (or even basal
archosauromorphs, which are subthecodont).  Curious how people who accept
without question Sharov's statement about the presence of an antorbital
fenestra never mention THIS observation of Sharov's...

Archosauromorphs have extra cervical vertebrae over the ancestral diapsid
condition of six: most archosauromorphs have at least 8 cervicals, and some
even more.  _Longisquama_ has the primitive six.  George, you're not a fan
of reversals.  So, did every group from trilophosaurids to rhynchosaurs to
choristoderes to pseudosuchians to pterosaurs to phytodinosaurs (I'll be
generous here) to "theropodomorphs" more advanced than _Longisquama_
indepedantly evolve 8 or more cervicals?  All this just so you can keep
_Longisquama_ close to the base of theropods?

I wished that Jones & co. had actually listed why they think _Longisquama_
was an archosaur, but they didn't.

Now, there IS something extremely interesting: the "furcula".  Unlike
theropod furculae it doesn't seem to be all grown together into a single
unit.  Instead, the two rami meet at the middle, and are presumably fused,
but they have a distinct line between them.  What's more, they also have a
clear glenoid-form articulation on them! (a flattened surface on each
ramus).  This got me thinking at first that this was some weird
scapulocoracoid, but the rami seem too symmetrical for that.  This element
MAY be fused clavicles, and thus a furcula.  Difficult to say.  I'd be
really interested to know what fit into that articular facet (an
interclavicle...?).

So, it's a great little beastie, but I'd like to see someone offer some
reason to consider it an archosaur, or archosauriform, or archosauromorph.
Crocs and champsosaurs are more bird-like than this baby.  I have an idea
where it might fit, but must await the proper analysis to see if it is
supported or not.

The integumentary elements?  These are really cool.  Unlike fossilzed bird
feathers, they always show a continuous margin, and at least some sections
show regularly spaced wrinkles: this leads me to suspect that these were
contiuous sheets of some material with a central shaft down the middle.
This is different from the construction of featers (a shaft with branches
with branches with branches), but who knows: maybe they were homologuous.

The paper in question is:
Terry D. Jones, John A. Ruben, Larry D. Martin, Evgeny N. Kurochkin, Alan
Feduccia, Paul F. A. Maderson, Willem J. Hillenius, Nicholas R. Geist,
Vladimir Alifanov.  2000.  Nonavian Feathers in a Late Triassic Archosaur.
Science 288: 2202-2205

The news article which accompanies it is:
Erik Stokstad.  2000.  PALEONTOLOGY: Feathers, or Flight of Fancy?
(The subtitle is "A contraversial paper aims to turn avian origins on its
head.  But mainstream paleontologists say "put up or shut up").

Later, folks.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843>