Dinogeorge wrote:
> No, it cannot. This is an assumption built into the cladogram by choice of
> outgroup. You choose a bipedal form as the outgroup, and sure, your cladogram
> will "prove" that the ancestor of the clade is a biped(!). The problem with
> most dinosaur cladograms is that they have many character polarities backward
> ab initio.
This is plain nonsense. Most non-dinosaurian archosaurs were obligate quadrupeds or (at best) facultative bipeds: crocodilomorphs, lagosuchians, rausiuchians, phytosaurs, proterosuchians, etc etc. These are the taxa that are used as outgroups. Your statement makes absolutely no sense.
> Semilunate carpal evolved at least twice in Maniraptora (segnosaurs and
> deinonychosaurs independently: Alxasaurus had no semilunate carpal, eg).
Uh-uh. No it didn't. The semilunate carpal evolved ONCE - in the common ancestor of all maniraptorans. Segnosaurs have it, oviraptorosaurs have it, deinonychosaurs have it, birds (of course) have it. Contrary to what you say, _Alxasaurus_ does have a semilunate carpal - it exists as two discrete elements, rather than the unitary structure of other maniraptorans.
> Reversed hallux evolved very early in theropods and occurs in all theropods at or
> above the ceratosaur level--look at theropod foot anatomy, fer chrissake, or at
> theropod footprints from the Triassic.
Well, this is dead easy to refute. Just look at the work done by Kevin Middleton on the theropod hallux.
Middleton, K.M. (2001). The morphological basis of hallucal orientation in extant birds. Journal of Morphology 250: 51-60.
This paper (when it comes out) should finally kill the myth that most theropods have a reversed hallux:
Middleton, K.M. and S.M. Gatesy. in prep. The origin of grasping feet in birds; A reinterpretation of toe reversion through theropod evolution.
I've read Middleton's 1995 thesis on this topic, so I think your idea is in for a lot of trouble. Those Triassic theropod footprints you mention DO NOT show a reversed hallux, and according to Middleton a true reversed (= reflexed = opposable) hallux does not appear until Aves.
> Feathers? We know nothing about the evolution of feathers from any
> cladogram.
Actually, we do. You may not understand what the cladogram is telling you. (See below.)
> But do you think they appeared fully formed by magic in Archaeopteryx?
Of course not. What an absurd thing to say! We see rudimentary feather-like structures in more basal theropods (e.g., _Sinosauropteryx_, _Shuvuuia_). Evolution transformed these structures into flight feathers. This is what the cladogram tells us. Quite clearly, in fact.
> Bipedality. I claim that many dinosaurs were bipedal because the forelimbs
> of their volant ancestors had become too winglike to be used for walking by
> their ground-dwelling descedants. Current models of dinosaur evolution provide
> NO reason for the appearance of bipedality in dinosaurs except the
> tautological one: they somehow made dinosaurs "better."
You must have overlooked the papers that discussed this. According to PUBLISHED STUDIES, the shift to bipedality correlates with changes to the forelimb, which improved the prey-catching ability of the hand (manus). There is no tautology or circularity to this.
Tim
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