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Re: birds or theropods



At 12:36 PM 11/25/96 -0500, Tracy Ford wrote:

>Why is it, that if a late Jurassic partial skeleton that looks like it 
>is either a bird or theropod, 100 % of the time put into theropods? 
>
>For instance _Palaeopteryx thomsoni_ JENSEN, 1981, is considered to be
>a Manoraptorian theropod, but also a possible Archaeopterygid. Why is
>it so hard to consider it a bird? There is some more small skeletal
>elements from Dry Mesa Quarry that could also be a bird.

Don't try and interpret the Padian & Jensen paper in a strictly Linnean
sense, since Padian (noted cladist) is an author on it.  The Dry Mesa
material is clearly a maniraptoran theropod.  Whether it is part of the
avian branch of the Maniraptora or the dromaeosaurid branch of the
Maniraptora (or some other branch of the Maniraptora) cannot be resolved
with the current material.  Birds ARE maniraptorans by definition, so if it
is a bird, it is also a maniraptoran.  However, not all maniraptorans are
birds, so it could be from a non-bird maniraptoran.

>If there are Non-avian Manoraptorian theropods, what are the Avian 
>Manoraptorian theropods? Birds?

Yes, exactly.  Avian maniraptoran theropods are called "birds".

>Why not go out an a limb and call Dromaeosauridae Avian Manoraptorian
>theropods?

I'd be happy to, provided I were presented by an analysis which placed
dromaeosaurids closer to modern birds than to some other form which was
unquestionably a bird.

>There are as many similarities between _Archaeopteryx_ and
>Dromaeosaurids IMHO as there are between Archaeopteryx and
>_Confuciusornis_.  Also, why not make Mononykus and Oviraptorids Avian
>Monoraptorian Theropods?

They may well be.  Perle et al. clearly interpret Mononykus as an avian
maniraptoran theropod, and some (Paul, Elzanowski) have considered
oviraptorids to be closer to modern birds than is Archaeopteryx.

>To me, we have to stop thinking of birds as birds are today, and think 
>of birds as what they were. Until then George's BCF theory will not be 
>accepted. I've talked to Witmore, Chiappe, and Olson, about that and 
>they see my point. 

Well, the birds of today DO form their own group (Neornithes of most
authors), so it is good to remember that, but yes: depending on where we
draw a line saying "above this point, they are birds", we will get different
animals within and without "birds".

>I also talked to Witmore about _Protoavis_ and asked what he thought,
>he told me that even if there is only one bone that is avian, then
>there was a bird in the Late Triassic.

But if none of the bones are avian, then there is no evidence for birds in
the Late Triassic.

>What is the problem with this?
>Hou, Martin etc NOW say _Archaeopteryx_ isn't the first bird, but must
>have evolved from an earlier bird ancestor, no kidding.

>I just bought 1 copy of The Puzzle of the Dinosaur-bird, the story of
>Archaeopteryx by Miriam Schlein and illustrated by Mark Hallet. Mark
>paints a Composognathus with feathers (good timing with the new
>Chinese feathered dinosaur), and Dromaeosaurus and Oviraptor with
>feathers, (ala Greg Paul), I use to not agree with this, but am now
>changing my mind and beginning to think Greg is right after all.

Same here.  (Actually, I've considered feathered coelurosaurs quite likely
for a long time, but am glad to have some phylogenetic evidence to back it up).

> This is a great time for Paleontology.

Agreed.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877