Re: Protoavis?

["Jonathan R. Wagner" <znc14@ttacs1.ttu.edu>]

At 07:04 AM 10/18/97 -0700, Jonathon Woolf wrote:
>* _Protoavis_ is usually reconstructed with the forelimbs held up and
>out, like a bird's.  However, if no details of the shoulder anatomy are
>known, how do we know which way the arms actually articulated?  They
>make sense either as unusually short wings or unusually long theropod
>hands.  
        What gives you the impression that no details of the shoulder
anatomy are known? Chatterjee has the scapula, coracoid, furcula, sternum,
and humerus of _Protoavis_. Sounds like a shoulder girdle to me. Laterally
facing glenoid in the house...

>* _Protoavis_ is always reconstructed as a biped.  A bipedal animal
        A quick look at the anatomy of the critter, as reconstructed by
Chatterjee, will probably convince you that, assuming his reconstruction is
correct, it is a biped.

>older than six million years can be one of only three things: a
>dinosaur, a bird, or some member of a group as yet unknown to science. 
        Since birds are dinosaurs, in your construction of the question, it
is either a dinosaur or it isn't.
        People waffle on pterosaurs and pseudosuchians being bipedal. We
ought not to completely rule them out. Also, if herrerasaurs and _Eoraptor_
are not dinosaurs, they should be included. And don't forget the various
dinosauriformes and dinosauromorphs (I can never get these taxa straight)
like _Marasuchus_.

>Why is that third possibility never mentioned?  
        Because it is unparsimonious. Randomly asserting the presence of
groups "unknown to science" when you cannot explain something is not a
scientific practice. If I said that every fossil I can't identify belongs to
a group unknown to science, I'd get laughed out of grad school. If one has
*evidence* that the critter is a member of such a group is one thing.
However, in the case of _Protoavis_, such evidence does not appear to be
forthcoming.
        Also, how does one find such a group? In a nutshell, every tetrapod
is related to all other tetrapods somehow. Therefore, they are all
assignable to tetrapoda, or to some group within tetrapoda. Therefore, the
very idea of a group of tetrapods "unknown to science" is fallacious.
        If another genus were present, and analysis indicated it shared a
more recent common ancestor with _Protoavis_ than with either did with other
animals then the *two* of them could be said to represent a group previously
unknown to science. However, the errection of groups (taxa) on the basis of
the phenetic distinctiveness of ONE animal with respect to all other groups
is an artifact of Linnean taxonomy, and does not have evolutionary
significance.    


>* Lessem's book KINGS OF CREATION (1992) makes it sound as if Chatterjee
>has never actually claimed this animal was a _flying_ _bird_.  At least
        Well, whatever he said then, or was quoted/paraphrased as saying
then, he now says it is a flying bird, closer to modern birds than is
_Archaeopteryx_.
        It was my understanding that he always believe it to be closer to
modern birds than _Archaeopteryx_, but I may be wrong...

>back then, Chatterjee apparently saw it as an early stage in avian
>evolution.  Chatterjee has never claimed that it was a modern bird, or
        Certainly not!

>even as advanced a bird as Cretaceous ichthyorniths.  As I understand
        "Advanced" is a concept which is often used in a manner inconsistant
with modern evolutionary theory. It implies all sorts of unjustified
assumptions about the presence of a "direction" to evolution. A more
appropriate formulation of your point might be "as close to modern birds as
are ichthyornithiformes."

>it, no one else has ever been able to make a detailed study of
>_Protoavis_.
        Now, don't make it sound like Chatterjee is trying to stop them...
        Has anyone tried? They may have been waiting for Chatterjee to
finish his preliminary work-up. Professional paleontologists have a whole
array of "common courtesies" which they follow, and they may just be wating
for Chatterjee to finish. The real professionals seem to have unending patience.

        "He will learn patience..."

>Chatterjee's opinion is (or until recently, was) the only
>informed one that exists.  So how did the lines get drawn as "it's 100%
>bird" versus "it's either a theropod or a chimaera"?
        Ok, last time: bird => theropod
        Chatterjees says _Protoavis_ => bird => theropod

Some people like _Protoavis_ because they think it means:
        bird not => theropod
They will not be happy when they read Chatterjee's new book.

>Is there no chance
>that _Protoavis_ is, say, a very early scion of the line that led to
>maniraptoran dinosaurs and through them to birds?
        There is certainly the possibility. There are a number of
possibilities. For example, Greg Paul has suggested that it is an
herrerasaur. Regardless, Chatterjee's interpretation of the anatomy of the
animal indicated that either it is a bird, or an astounding ammount of
convergence has taken place. Judget he evidence for yourself.

>* The bones of _Protoavis_ were found jumbled into sandstone nodules,
>completely disarticulated, which is why some people think it's a
>chimaera.  What are the chances that it's reworked somehow from Jurassic
>sediments?
        Zilch. There is a basic stratigraphic principle, the "principle of
inclusions" which is a special case of the principle of cross-cutting
relationships. It says that rock has to exist before it can be included in
other sedimentary rock. Reworking is the process of weathering fossils or
rock contaning fossils out of rocks already present, trasporting them, and
redepositing them in sediments which are later lithified as new sedimentary
rocks. Since your "Jurassic nodules" would have been formed AFTER the
Triassic sediments of the Dockum Group, they could not have been reworked
into the Dockum sediments as inclusions.
        To illustrate this, make a plain pie, then try to put the cherries
in after it is baked.

>My personal feeling on _Protoavis_ is that it might be a bird, a
>theropod, a birdy theropod, or something else --
        Birds => theropods. Making an artificial distinction between the two
will only confuse the issue.

>but if you want me to
>accept it as a bird, find me one with feather imprints.  Nothing else is
>going to clinch it.
        That is wholly unreasonable. If we insist on feathers for every bird
fossil, we'll have to drop a lot of them from the books. Where are your
_Ichthyornis_ and _Hesperornis_ feathers (at least, I thought they weren't
found with feathers... I could be quite wrong on this...)?
        Paleontology is founded on comparative anatomy. We can determine the
affinities of an animal without feather impressions, carbonized traces, or
Paul Davis' bacterial traces. For over a hundred years, we have used bones,
often not even complete skeletons, to discern the affinities of long dead
animals. If we decide that we will not accept anatomical evidence without
evidence for feathers, we pointlessly discard not only the entire history of
paleontology, but its philosophical, logical, and scientific basis as well.
        Also, as may yet be the case with _Mononykus_ (assuming those beta
keratin tubes have been correctly evaluated), the presence of feathers may
not necessarily tell you whether something is or is not a bird. If non-avian
theropods had feathers, your argument collapses.

        :)
        Wagner
----------------------------------------------------------------------------
    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
        "There's a fine line between stupid and clever."  -- Spinal Tap