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Re: kellner's ankle abstract



All the answers you seek can be found on the web or in the literature, Jaime. 
If you don't find them there, you can always seek more in the specimens 
themselves.

DP

"Jaime A. Headden" wrote:

> David Peters (davidrpeters@earthlink.net) wrote:
>
> <Interesting assumption.  IMHO this is the same reasoning that Feduccia et
> al. use when they say that there's a bird ancestor out there, we just
> haven't found it yet. In other words, you might be inventing an
> explanation for the lateral toe when no invention is necessary. I remember
> when some of the head honchos were saying that pedal digit V was somehow
> genetically linked to manual digit IV and when one elongated, the other
> did too.  Yes, I scratched my head at that one too.>
>
>   I didn't, since it makes sense from a developmental point of view.
> Development of the toes and fingers use largely the same control regions
> and Hox expressions, both being dominated by sonic hedgehog, etc. In
> matters of elongation, for example when TWO phalanges can equal or exceed
> the length of a four to five-phalanx digit, the issue based on the
> ancestral Saurian condition is one of elongation of the elements. No
> evidence has arisen from fusion, nor do I think one can prove this without
> an ontogeny (which Peters (2003, 2004) has refuted any other attempt to
> elucidate aside from his own -- the *Pterodaustro* bonebed has been known
> for several years, actually).
>
> <Another point: phalanx reduction can come about two ways: via loss or via
> fusion. The "loss" of one wing phalanx in Nyctosaurus comes about via
> fusion of m4.2+m4.3 for instance. M4.4 remains pretty much the same in
> morphology. When I mentioned that to Greg Brown, he said, funny, he had
> never thought of that possibility. IMHO>
>
>   Prove it.
>
>   Phalanx reduction (or increase) or loss both occur in a developmental
> way, and both provide means of testing:
>
>   1) development of a digit can be accellerated by sustained expression of
> shh in the limb bud, through the active condensation zones. In bats, this
> causes extremely developed metacarpals and phalanges of the manus.
>
>   2) development of a digit can, conversely, be retarded by limiting the
> expression of shh in the limb bud, through the active condensation zones.
> This may or may not be affected by the Hox genes in which one condensation
> can be lost, for failure to express the genes nccessary to start a finger,
> and the identity of digits may actually shift over to compensate.
>
>   3) limited, but well-expressed development in a digit can cause distal
> condensation to cease, in which the more proximal elements take up the
> role of the distal most elements, usually unguals. This occurs in mammal
> digits, and why even carnivorans have claws despite thier 2-3-3-3-3
> phalangeal pattern.
>
>   4) exaggerated development of digital condensation can possibly cause
> multiple phalanges to be expressed instead of the "norm", as happens
> during identity shifting, and may be why whales and ichthyosaurs, among
> others, have so many phalanges.
>
>   5) duplication events can cause the identity of a bone to be repeated in
> series, say for an interruption then later re-expression of the control
> genes on the growth plate, but only in series, hence the polydactyly of
> some amphibians, ichthyosaurs, etc.
>
>   Apply any of these developmental pathways to pterosaurs, then test.
>
> <the same thing happens in ptero feet. Two short phalanges make one long
> one on digit V.>
>
>   Based on what evidence?
>
> <Why not go with the more parsimonious answer that the bird=dinosaur crowd
> is pushing? i.e. Cladistics doesn't find ancestors exactly. Cladistics
> only tells us, from all of the possibilities we input, which makes the
> best sister taxa.>
>
>   No, this is not particularly correct. _Paleontology_ doesn't pretend to
> know ancestors, because an ancestral form in the fossil record could just
> as easily be a descendant of a lineage arising from that same ancestor,
> and not BE the ancestor, or member of the ancestral population. Cladistics
> finds that with a branching tree, which is expressed by means of grouping
> groups of data (OTU's) together, even a 0.001% variable between sister
> groups can still BE sister groups, mutually exclusive populations, as
> exists between several South American barbets which nonetheless show
> distinct plumage for all that they are genetically virtually
> indistinguishable. Yet natural selection has developed one population,
> apart from is parent population, and by the nature of taxonomy, they
> become subspecies of the same species, mutual, even if one was ancestral
> to the other. Cladistics finds only the "common ground," and cannot tell
> you which species arose from which, only biogeography and observation of
> evolutionary speciation events (in this case, sympatry).
>
> <And there are better matches in the protorosaurs than anywhere in the
> archosaurs -- at present. They just haven't been input that often.>
>
>   This is based on a biased opinion no one else has yet supported in print
> since 2000, either the interpretation of pterosaurs or the relationship
> with "prolacertiforms" or "protorosaurs."
>
> <Of course you can always wait for a better archosaur. Lots of people are
> doing just that.>
>
>   No one is waiting for the "better archosaur." They are using what data
> they have that they can agree on, and sometimes don't, but can verify by
> methods available elsewhere. So far, the latest trees from Peters,
> available freely on the web, have no accompanying support, and in fact,
> cannot be tested at this point. Thus ... heh ... it's not a scientifically
> viable hypothesis -- yet.
>
>   Cheers,
>
> =====
> Jaime A. Headden
>
>   Little steps are often the hardest to take.  We are too used to making 
> leaps in the face of adversity, that a simple skip is so hard to do.  We 
> should all learn to walk soft, walk small, see the world around us rather 
> than zoom by it.
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
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