Re: New alvarezsaurid

["Jaime Headden" <jaemei@hotmail.com>]

<<<...BCF says that the lineage from basal dinosaurs to modern birds 
were small, arboreal/scansorial creatures that spit off larger 
terrestrial lineages, right? Alvarezsaurids would just be another one of 
these lineages.>>>
 
<<And why they could _not_ be the antecendants I don't know,>>

<Since when are alvarezsaurids, a highly derived group of Late 
Cretaceous animals, considered as possible bird ancestors?>

I may have been a bit rash when saying this.

<<but *Shuvuuia* seems to be the first to have a prokinetic snout,>>

<Isn't it from the Late Cretaceous? In fact, the web article I saw
mentioned 70 million years ago, which would be Maastrichtian. Plenty of 
modern-type birds around by that point.>

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.

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. Morphology of the scapula and coracoid 
seems quite similar to *Avimimus*, and *Microvenator*, who I've had the 
fun of researching lately. The teeth of *Shuvuuia* are leaf-shaped and 
serrated, much in the form of troodontids.

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.

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.

Jaime A. Headden

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