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RE: Cladistic Idea



With a complete fossil record your idea would work great.  The biggest problem 
I see is that the record is not complete, for dinosaurs at least.  Just think 
of all the clades whose early/basal members are poorly known, or those whose 
basalmost members lived later than some of the more derived ones.  This would 
mean some characters would be unknown for clades if sampled early, and the 
primitive state of many clades would be miscalculated.  These would lead to 
different trees than the complete taxon sample, and not in a way that is likely 
to reflect a more correct topology.

Mickey

----------------------------------------
> Date: Tue, 12 Jul 2011 00:58:57 -0300
> From: gahrdng@mta.ca
> To: dinosaur@usc.edu
> Subject: Cladistic Idea
>
> I've had an idea about a new way of approaching cladistic analysis. I don't 
> know
> as much about the subject as I'd like to, so forgive me if this is a 
> ridiculous
> suggestion.
>
> It seems to me that it would be interesting to approach a cladistic analysis 
> of
> fossil taxa one age at a time. As an oversimplified example, imagine an
> analysis of ten fossil taxa, named "A" through "J". Imagine that
> stratigraphically, they are arranged like this:
>
> epoch #5: J
> epoch #4: G,H,I
> epoch #3: E,F
> epoch #2: D
> epoch #1: A, B, C
>
> The standard way to do a cladistic analysis would be to take all ten taxa, 
> score
> them for all the characters, and away you go. My suggestion is to consider the
> fauna of each age only in light of what has come before.
>
> Thus, in this example, we would first do an analysis of the earliest taxa: A, 
> B,
> and C. Once we got a tree out of that analysis, we would then add taxon D to 
> the
> analysis -- but constrain the tree so that A, B, and C had to stay in the
> topology that came out of the first analysis. Then we would add taxa E and F 
> to
> the analysis, but constrain the tree so that A, B, and C had to stay where 
> they
> were placed in the first analysis, and D had to stay where it was placed in 
> the
> second analysis. And so forth, adding the fauna of one age at a time,
> constraining the older taxa to stay in the topology of previous analyses.
>
> I know that time is a variable usually left out of cladistic analysis, on the
> basis that the fossil record will always be incomplete. But I think that this
> is an interesting way of incorporating it.
>
> After all, evolution has no foresight, and any new evolution of taxa has to be
> built on that of the past. Thinking about it another way, would a knowledge of
> how life will evolve in the future help us reconstruct how it evolved in the
> past? No -- each age has to be considered on its own terms, in light of what
> came before it, not what came after it.
>
> At the very least, it would be interesting to compare the results of an 
> analysis
> like this with the results of a standard analysis.
>
> And now here's someone to explain why this is a ridiculous idea and wouldn't
> work.
>
> Thanks for reading,
> -Grant Harding