Re: New alvarezsaurid

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

>Both Enantiornithes and Ornithurae are dead-end lines that did not 
>develop all the characters relavant to Neornithes, including loss of 
>true teeth, the keel, and pygostyle. Enantiornithines, of which 
>constituency seem closer to Archie than other bird groups (*Sinornis*, 
>*Patagopteryx*, *Eoalulavis*, *Protarchaeopteryx*, etc.) simply are to 
>un--bird-like in the structure of their limbs, pelvises, and skulls.

    1) Neornithes is included inside the Ornithurae. They are united by 
a procoracoid process, long sternal sulci, disto-proximal 
tarsometatarsal fusion, among many other things. You can trace the 
lineage of the ornithurines up from Liaoningornis, Chaoyangia, 
Hesperornis, Ambiortus, and Ichthyornis to modern birds.

    2) Protarchaeopteryx is not an enantiornithine.

    3) Regardless of the enantiornithines position systematically, they 
are birds. Cathayornis shows many bird-like features in the skull : 
enlarged fromtal, supraoccipital butted against parietal, reduced 
parietal, ventrally positioned foramen magnum, and an orbital recess on 
the quadrate. Cathayornis is a typical enantiornithine so these features 
are valid for the whole group. All enantiornithines have a pygostyle, 
sternal carina, carpometacarpus, heart-shaped ulnarae, strut-like 
coracoid, etc.  

><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.>
>
>This is seen in oviraptorosaurs, with a few added surprises, including 
a 
>palate set below the maxillary rim, form of the pterygoid, and several 
>fusions within the lower cranium that (while marketedly not true avian, 
>certainly closer than the enantiornithine ankle where *Oviraptor* has 
>one up on *Cathayornis*) form the palatine structure seen in birds.

Wrong. Though the oviraptor quadrate is birdlike, it is not 
streptostylic and the bar is mainly that of the quadratojugal. The 
oviraptor tarsometatarus exhibits no fusion too.

><<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?>
>
>Because the closest two groups physiologically to alvarezsaurids are 
>avimimids and oviraptorosaurs (perhaps by my definition and equivocal, 
>but the evidence for relationship is there, just as obscure as how 
>*Hesperornis* but for a few characters, was considered the antecendant 
>of grebes and loons, now seen as remarkable convergence) and that both 
>groups lack the carina or keel of the sternum, while possessing 
>ratite-like sterni and bird-like forelimbs, as well as a tendency to 
>produce the avian-style ankle.

    Hesperornis definitely came from flying ancestors. The most basal 
hesperornithiform, Pasquiaornis, has a shoulder like that of a volant 
bird. 

><Alvarezsaurids are oviraptorids that turned into birds?>
>
>I must say, I was surprised when my figures pointed that way. I will 
say 
>that I did not intend to gear my protocols towards this relationship, 
>but compared oviraptorosaurus to troodontids, ornithomimids, 
>archaeopterygids and dromaeosaurs (even *Unenlagia*) and 
Alvarezsauridae 
>and Avimimidae.

    Avimimids are chimeras. 

>
>Flight is not a prerequisite bird character, so ratites are birds, and 
>so is the penguin group. Ornithurines are birds, though they have 
teeth, 
>and enantiornithines are birds, even though they have the 
reversed-ankle 
>system. _Lacking_ a certain character does not occlude it from this 
>clade. And protobirds, not birds, would be my reference.

    Lacking many, many, many, many, many, many, avain characters 
excludes them from Aves.

><<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.>
>
>This conclusion is based on evidence that lacks evidence to the 
>contrary, but lacks the final proof of its reality, so it's equivocal; 
>I'm not saying it's true.

   The evidence is still misinterpreted. What you are viewing as valid 
characters are demonstratebly convergences when you look at the avian 
family tree.

><We can trace the "gathering" of neornithine traits quite clearly. All 
>birds had a reversed hallux,>
>
>including alvarezsaurids and oviraptorosaurs

   But they do not have a reversed hallux ( oviraptors don't ). Read 
Norell and Makovicky's dromaeosaur paper and they discuss the 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.>
>
>Domestic flightless chickens have been around for centuries, they don't 
>fly, and they have a very large keel.

    Chickens still do fly for short distances. Anyway a paedomorphic 
change is associated with the loss of flight and this includes loss of a 
carina. 

><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.>
>
>Yes, it is. But which groups get to stay in it, and which not?

    Alvarezsaurs stay in because  they have many avian characteristics 
that oviraptorosaurs lack.


MattTroutman

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