Re: _Archaeopteryx_

[jdharris@teal.csn.net (Jerry D. Harris)]

Phillip et al -

> Or it may indicate a more derived sister group that predates
>_Archaeopteryx_.  In other words, > Archaeopteryx may represent a
>plesiomorphic dead-end branch
> in the Aves tree.  If this is ever proven true, it wouldn't be the first
> instance of this happening in fossil record.

        I acknowledge that this is a distinct possibility, and many have
suggested this.  Lacking clear evidence to the contrary (the reported new
Chinese fossils nothwithstanding barring a formal description!), I would
have to say that on the face of it this is as good an explanation as any.

        However, IMHO, the transitional series seen in the Late Jurassic
and Early Cretaceous doesn't support the contention that _Archaeopteryx_
represents a "dead-end" branch of avian evolution.  For example, when you
compare the salient pectoral features of _Archaeopteryx_ with other birds
later in the temporal sequence, what you see is a clear and nicely laid out
evolutionary sequence:  no ossified (or small ossified) sternum and a
simple, U-shaped furcula in _Archaeopteryx_, a slightly larger sternum and
a furcula with a hypocleidum (the fused "handle" of the wishbone) in
_Sinornis_ and _Iberomesornois_, and then much larger sterna in _Concornis_
and _Ambiortus_, which also possess fully avian furculae.

        Of course, just to complicate matters, many people seem to think
that the Chinese and Spanish birds are representatives of the
enantiornithurine radiation of Cretaceous Aves, and not along the line to
true birds.  I'm still personally trying to sort out the suite of purported
enantiornithurine birds, and what they mean to avian evolution, and so
can't speak to them yet.  It's even been contended that _Archaeopteryx_ is
an enantiornithurine (the first one), and led to that radiation of birds,
while _Protoavis_ is a true bird and led to the rest of modern Aves.


Jerry D. Harris
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO  80205
(303) 370-6403

Internet:  jdharris@teal.csn.net
CompuServe:  73132,3372
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        "I repainted the picture Brown had painted for us.  A dying,
shrinking lake...these great...behemoths...dying..."
        "Well," she said, "all you tell me may be so...but I still can't
see why such creatures would have wanted to do it in the first place."
        "Do what, ma'am?"
        "Why, crawl away back under all that rock to die."

-- Roland T. Bird, _Bones for Barnum Brown_
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