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Re: Reevolving bones?



Tracy Ford wrote:
>So in order for Therizinosauroidea to be a theropod, it would have to have
it's >metatarsal I, which in your view was just cartalagous in it's
predessors (which >would have to include the whole toe for it to work), then
MT 1 re-'boneized'. 
        The reossification of elements is pretty much a given (IMHO) in the
geological record. The presence of bony sterna in some dinosaurs which seem
to be descended from ancestors which lacked them can be explained by the
element being present in cartilagenous form in predecessor species. This
seems to make even more sense when you factor in that the sternum appears
(IMHO) to be ossified in association with quadrupedal locomotion in more
basal forms.
        This is, however, by *no* means a requirement for therizinosaurs.
They may have re-evolved their first metatarsal by some other process
(retaining and ossifying the element from an earlier ontogenetic stage).

>Then all thereopods have a cartalagous MT 1 so it had a 'phatom' toe.
        No.

>Just another way for cladist to explain something to fit what they want,
and >not to see who impossible it really is.
        More like, just another way for someone who apparently isn't
thinking about evolutionary pathways to take a cheap shot at someone who is.

>Reevolving a toe, that was totally >lost, to be exactly the way it's suppose to
>be is totally insane. 
        If you read the _Alxasaurus_ paper, you will note that the first
metatarsal of therizinosaurs is *not* "exactly" like that of other four-toed
dinosaurs, and actually (by some miracle of evolution) records its re-evolution.
        You really should stop getting all of your data from George ;).
Dollo's Law is not a law in the strictest sense. The fact that ontogeny
recapitulates phylogeny allows evolution (in some cases) to dip into the
evolutionary history of an organism and reform structures which may be more
useful than the ones the animals has now. Accept this now, or doom yourself
to never understanding evolution.

>Is there any modern evidance to support this? In living genera?
        Birds appear to be descended from ancestors which, at some point
either possesed cartilagenous forms of or had completely lost their furcula
and sterna. Hopefully someone else will come up with a less... controversial
example.

       "And the angel appeared before Hennig and said,
        'Behold Hennig, I give unto you the sword of parsimony,
        Klados, that you may go forth and rend from man
        The Unnatural Groups he hath made in defiance of us."
        And Hennig went forth and cleft the Groups of Man,
        Rending every one into two, and each nought into a one;
        And he strode amongst the dragons of the sea and air,
        The great beasts of the plain and the serpents and the fishes;
        And in each was found the novelty which told it's path upon the Earth,
        And for each beast he carved a place for it and its progeny."
                ---With all due respect to Hebrew Tradition.
----------------------------------------------------------------------------
      Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock TX 79409
      "The cost of living hasn't affected its popularity." - Unknown