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RE: Ah ha! That's where therizinosaurs came from



Thanks Jaime,

Good points. I think it was Witmer who wrote on this methodology, and
called it phylogenetic bracketing.

I wonder what would happen if we applied phylogenetic bracketing to Xu's
new Xiaotingia cladogram. You have Epidexipteryx, quite certainly
flightless, at the base of the Avialae, and Archaeopteryx, quite possibly
flighted, at the base of Deinonychosauria, so what can we infer about
their last common ancestor? The next successive outgroup are the
flightless Oviraptorids, right, so if we take that little tree there we
may argue that flight arose twice: once after scansoriopterygids and once
in Archaeoopteryx. That's nutty, but then Biology is nutty.



>
> Jason Brougham wrote:
>
> <But cladograms don't tell us the actual ancestors. They tell us the
>  sister groups, and if you found an actual ancestor, as improbable as
> that is, it would show up in a cladogram as a basal sister group. So, I
> guess, this debate is outside science. There is no rigorous or empirical
>  scientific method that can demonstrate if an animal had a flying
> ancestor or not.>
>
>   It has been argued, although I cannot exactly recall where, but Paul may
> actually have said this (_DotA_?), that we should be able to extrapolate
> an "ancestor" on the basis of inferences from the two sister taxa and the
> most restrictive node they share (because Paul eschews cladisitic
> terminology, I'm actually using my own words for the generalized concept
> here, which essentially argues that two relatives can present an ancestor
> by the fea6tures they share in common -- we would expect their ancestor to
> have them). Moreover, however, we can also take their next sister taxon
> and infer the features our two initial forms have that that ancestor
> lacks. This is essentially cladistics, an algorithm performed at each
> potential taxon+taxon<taxon junction. So it is in general part of the
> predictive element of Science to determine how we can know, even if we
> should not infer a true ancestor when considering phylogeny in general.
>
>   This becomes more complicated and less theorietical ancestral finding
> when one takes this practice to the hereditary level and looks at
> individuals or very small time scales, and has been adapted by workers
> looking at human ancestors. There is a tendency, as in the question of the
> origin and relations of *Australopithecus africanus*, *afarensis* and
> *anamensis* and the arising of *Homo*, to treat the taxa as parts of
> anagenetic lineages rather than sister taxa, and that many of these forms
> are segments along these lineages. This has been most extreme in
> attempting to determine exactly how one identifies *Homo* in the fossil
> record. In short, this is a conflict between cladistic methology (which
> removes the assumption of true ancestors) and heredity (which assumes they
> must actually exists and that we recover fossils of them). Both can be
> true, but the methodology of Science cannot easily distinguish them. This
> has recently been of some issue among the dinosaur community due to the
> work of Scannella and Horner, as they argue *Triceratops* includes all [or
> most] Hell Creek and equivalent (Lancian) ceratopsids from North America.
>
>   Phylogeny reconstruction is actually very complicated, but
> ancestor-descendant relationships are not: one must be controlled by
> objective processes, while the other is based on subjective inferences.
> The relation between the two, evident no less in the *Triceratops* Lumping
> Event of 2010 [and ridiculously overblown by some certain vociferous DML
> writer] is what I call "The *Homo* Problem" and I will eventually get back
> to this.
>
>   Nonetheless, I must actually say the problem is (or can be) within
> Science, but that the situation has to be looked at in different ways. A
> position may be selected from among them, but it must be congruent with
> the data and be arrived at independently using the same methodology
> employed in the first case (or by the application of better predictive
> inferences). I do not think Paul's inference of flightlessness in taxa
> basal to the rise of birds (as recovered by cladistic analysis) is
> usefully scientific, simply because there is no way to distinguish the
> criteria employed, as I have said before and Jason (below) writes:
>
> <It helped me realize that there is no single feature that is
> unambiguously associated with volant taxa. Not a furcula, not a
> triosseal canal, nothing. Rather it is more a matter of proportions
> between the elements: long arms, big pectoral girdles, etc.
>
> Therefore we cannot prove that ratites had flying ancestors based on
> their skeletal morphology. Nothing in their skeleton proves that they
> don't retain the primitive condition of the avian lineage before they
> attained flight.>
>
> Cheers,
>
>   Jaime A. Headden
>   The Bite Stuff (site v2)
>   http://qilong.wordpress.com/
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a
> Billion Backs)
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org