Re: New alvarezsaurid

["Matthew Troutman" <m_troutman@hotmail.com>]

>Archeoptegerids, hesperornithiformes, enantiornithines, etc.. All 
>extinct lines of avian evolution, though impressive in that each group 
>came up with something none of the others did, such as the fully 
>reversed hallux, or fused carpometacarpus, keeled breastbones, loss of 
>teeth, and so on. While very similar in appearance to monder avians, 
all 
>these had teeth, clawed hands (*Eoalulavis* got the first alula, 
though, 
>and lost the thumb claw in the bargain) none of these have that 
>prokinetic snout.

    All ornithirines had a prokinetic snout as shown by Witmer and 
Martin. The new enantiornithine described by Sanz et al. had a very 
ornithurine-like quadrate with a prominent orbital process; the jugal is 
also reduced to a jugal bar in that enantiornithine. Cathayornis seems 
to have all of the features of the new enantiornithine with another 
feature: an ossified mesethmoid, which marks the development of a 
bird-like nasofrontal hinge in enantiornithines. Archaeopteryx lost the 
ascending process of the jugal and squmosal-quadratojugal contact and 
had a relatively more adavanced quadrate, all of which suggest a 
primitive system of kinesis.

>Alvarezsaurids came up with the keel and opisthopubic pelvis, it seems, 
>independent of the hesperornithiforms or whoever else developed the 
keel 
>back before the K-T boundary.

   Why does it seem that they evolved it independly of other birds? 


>What we have here is a lot of "avian" groups producing one, two, or 
>several characters thought to be distinctly bird-ish. BCF would say 
this 
>supports their case, and indeed it does, but what if it means that 
while 
>all these groups were playing with the various characters but not 
>getting the right number of them to turn them POOF! into birds, as per 
>Fedducia? Yes, they could do that, and more. One line, not so 
bird-like, 
>such as avetheropods (as opposed to maniraptorans) such as 
>oviraptorosaurs, who have a variety of characters unique to birds, 
>including the palate structure, who are morphologically similar to 
>alvarezsaurids like *Mononykus*, *Patagopteryx*, or *Shuvuuia*, who all 
>have avian characters in the sternum and skull. And these in turn could 
>give rise to smaller, longer-armed creatures who continued to reduce 
the 
>tail and eventually formed a pygostyle, and the skull, of course, 
needed 
>to change only slightly. So, BADD has its merits.

    Alvarezsaurids are oviraptorids that turned into birds? First of 
all, I don't think that oviraptorids had a triradiate palatine or any 
other of the palatal features of birds. 

>So birds could have arrived from theropods, and have turned into 
>theropods, all at the same time, and the group we commonly think of as 
>birds would have to be reconsidered. The fact is, all three theories 
>have their salient (and equivocal) points, and what we may actually 
have 
>today is two different lines of evolution that have horrible converged 
>upon each other, or one line that arrived from a hitherto-unknown line.

   This conclusion is based on misinterpreted evidence. We can trace the 
"gathering" of neornithine traits quite clearly. All birds had a 
reversed hallux, it was lost in hesperorithiformes just as it was in 
loons and grebes. The keeled sternum was also lost in 
hesperornithiformes because it did not use its forelimbs for anything. 
Enantiornithines have a carina, though it is in a posterior position as 
opposed to the ornithurine anterior. The similiarity of the 
scapulacoracoid in oviraptorosaurs and alvarezsaurs is actually just a 
similiarity that is brought on by the flightless nature of alvarezsaurs 
( compare a Diatryma scapulacoracoid to a Tyrannosaurus and see the 
convergence ). Aves is clearly a natural group. 

MattTroutman

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