Re: Protoavis?

[Jonathon Woolf <jwoolf@erinet.com>]

Fascinating.  It's been quite a while since I saw a reply to one of my
posts in which the replier did such a comprehensive job of jumping to
wrong conclusions and substantively misinterpreting just about every
line.  

Jonathan R. Wagner wrote:
 
> 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...

The only photograph I have of _Protoavis_ is in Lessem's book.  It shows
skull, forelimb, a nearly complete spine, most of a hindlimb below the
knee, and a partial sternum.  Nothing else.  

Incidentally, I did say "_IF_ no details of the shoulder anatomy are
known".  If.  Conditional.  As in, "I am not sure this is true, but
assuming it is, then . . ."  It would have been relatively simple to
just say "we do know something of the shoulder anatomy," without getting
snotty about it.

> >* _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.

My point exactly.  I was not questioning the bipedal reconstruction; I
was stating it as a precondition for a sequence of reasoning.

> 
> >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.

Birds are a discrete subgroup of dinosaurs.  In vernacular usage, saying
"bird or dinosaur" is quicker and easier to understand than saying
"avian theropod dinosaur or non-avian theropod dinosaur."  

> >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.

I think somebody is trying to be a righteously pedantic s.o.b. here.  I
think my meaning was clear: there is at least a possibility that
_Protoavis_ is the sole known member of a lineage of tetrapods for which
no other member is yet known, so nothing can be clearly known of its
evolutionary history or its relationships to other tetrapods.  

> >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

Semantic quibbles again.  Avian theropod vs. non-avian theropod or
chimaera.  Satisfied?

> >* 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.

I don't need a lesson in basic stratigraphy, Professor Wagner.

In Britain, Cretaceous mammals and other small animals are often found
in infilled cracks in Carboniferous strata.  

Picture this:

Time: Cretaceous Period

        Jurassic sediments 
        -------------------------  <- _Protoavis_ source strata
        ----------------------------
        -------------------------------- River flowing this way->
        --------------------------------------                  _Protoavis_ 
found here
        --------------------------------------------                    v       
        ----------Triassic sediments under Jurassic sediments
------------------------------

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Why is such a scenario impossible?  Or even implausible?  Does the local
stratigraphy rule it out?  Please don't assume I'm trying to be
argumentative -- the simple fact is I don't know and I want to find out.

> >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...)?

You're jumping to conclusions again.  I am not saying that _no_ fossil
is acceptable as a bird unless it had feathers.  I am saying that in my
mind, PROTOAVIS is not acceptable as a bird unless somebody shows it had
feathers.  Extraordinary claims require extraordinary evidence.  A bird
in the Cretaceous is not an extraordinary claim.  A bird in the Triassic
is.  

-- JSW