Re: "Dinosaurs Died Within Hours After Asteroid Hit Earth..."

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<And to the phylogenetic assignments that follow from them? Should it
really be _completely_ irrelevant to those?>

  Age can be used to calibrate phylogeny, but not morphology. My point,
which is being reiterated here since the _last_ time I responded on this
thread, is that the morphology preceeds arguments of age, and age should
only be used to calibrate this, as in gene trees being calibrated
temporally.

<It was explicitely said to be a crown-group parrot. If it's not one, it
seemingly can't be a psittaciform at all... as I wrote, I have yet to copy
and read the *Psittacopes* paper.>

  Stidham (1998) wrote:

  "Here I describe a toothless avian dentary symphysis (fused jawbone)
from the latest Cretaceous of Wyoming, United States. This symphysis
appears to represent the oldest known parrot and is, to my knowledge, the
first known fossil of a ?terrestrial? modern bird group from the
Cretaceous." (pg. 29)

  and

  "The discovery of this parrot in the Lance Formation indicates that the
lineage leading to the parrot crown group was present by the end of the
Cretaceous. If this parrot were a lory, as suggested by its morphology,
the most recent common ancestor of the psittaciform crown group would be
placed in the Cretaceous (Christidis et al., 1991), as supported by
molecular data11. The occurrence of a parrot in the Cretaceous implies the
presence of other closely related bird taxa in the Cretaceous, as also
predicted by molecular divergence data (Cooper & Penny, 1997; Hedges et
al., 1996)." (pg. 30)

  Nowhere in his work does he call it a crown-group parrot, just a
"parrot," as was also clear from his response to Dyke and Mayr (1999) in
_Nature_:

  "I have presented a hypothesis for the identification of a Late
Cretaceous fossil as the oldest known parrot (Stidham, 1998)." (pg. 318)

  and 

  "If non-crown-group parrots are present in the Eocene (Mayr & Daniels,
1998), then the sister group to those taxa (the stem leading to the crown
group or the crown group itself, possibly with a modern-looking jaw) must
have been present by the middle Eocene as well. The identification of the
Cretaceous jaw as a parrot is subject to test and refutation, like any
hypothesis. However, the accepted methods of the field, not statements
about gaps in our current knowledge and preconceived notions of character
evolution, must be used to falsify hypotheses and generate alternatives."
(pg. 318)

  The last two sentences are especially important in this discussion. His
sentence in his first paper, "[T]he lineage leading to the parrot crown
group was present by the end of the Cretaceous[.]," is an example of this.

<1. I'm waiting for someone to test the hypothesis that that fragment
could be a ceratopsian instead. This is not adequately addressed in the
paper.>

  I have been trying to "prove" it's an oviraptorosaur, since it actually
shares similarities to that group. No ceratopsian has a scooped, scalloped
predentary or rostral, which possess keels in nearlly all taxa. The
posterior margin of the bone is non-sutural, and shows medial foramina
showing it was NOT covered by another bone. The bone lacks the caudal
ramus of the predentary, and it is unlikely this element is in anyway
ceratopsian in nature. The distinct morphology of the rostral and
predentaries have, I beleive, prevented anyone from comparing the element.

<2. Unlike the Eocene (of the northern hemisphere at least), the Jurassic
of northeastern Australia -- the place is supposed to have been rather
isolated -- is very poorly known, so big surprises are considerably more
probable there than in the Eocene.> 

  So? This is a massive gap that shows a lystrosaur-like morphology is
present WELL after the demise of all other known dicynodont taxa. It shows
that the morphology is consistent, but seemingly countered by its age. The
snout fragments of the Australian dicynodont provide a lazarus taxon,
whereas the Lance jaw provides the opposite condition: a "modern"
morphology may be present in an older, far older, condition. The Eocene
taxa may be the lazarus group of a more primitive morphology. Mayr,
though, seems to consider that the Eocene taxa represent the oldest,
simply because they look "primitive" enough, compared to crown-group
parrots.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
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