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Re: Cladistics (was Sci. Am. - present)



Matthew Troutman wrote:
>    Uncinates are absent in osseous form in Archaeopteryx, 
>Confuciusornis, and enantiornithines. Some have speculated that they may 
>have been cartilageous; possible, but unlikely. 
        Why unlikely?

> Note: the uncinates in dromaeosaurs seem to be seperate ossifications 
>which makes them questionable. 
        Why? Nature is repleat with examples of derived bone morphologies
manifested as seperate ossifications/new ossifications: ceratopsian
horncores, the ceratopsian rostral and epioccipitals [sic?], apparently the
avian astragalar ascending process, etc. etc. Just because something is a
seperate ossification does nt necessarily call its homology into question.
Think of it this was, if uncinates truly are important for birds, maybe they
were less important for dromaeosaurs. As a consequence, lack of fusion of
the uncinates to the ribs may be explained by the possible lack of selection
pressure to maintain fusion (or evolve fusion, depending on how you look at
it).    

>[croc uncinates] are cartilageous and may not be homologous to bird uncinates.
        So, although both living anchors of the archosaurian Extant
Phylogenetic Bracket possess uncinates, and in one of them the processes are
cartilagenous, you still deem it unlikely that basal birds had cartilagenous
uncinates? I would now be *very* interested in your reasoning.

        :)
        Wagner
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    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"Cladism is to evolution what agnosticism is to the existance of god"-Horner