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Re: Therizanosaurs + Cladistics



>    I am also not to enthusiastic about cladistics (if you haven't noticed)
>because, as I have said before, they tend to split up ancestor-descendant
>lineages into sister groups with an as-of-yet-undiscovered common ancester to
>both as the node at which they both appear; leave out animals that are very
>close to the ultimate ancestor of a stock with the phrase "The most recent
>common ancestor of both this and that;" and place too much of an emphasis on
>the most evolved by bestowing upon it the most titles (I believe this is
>refered to as nesting).

As I understand it, a clade is supposed be represented by a particular
species and everything which descended from it. The problem is that it is
very hard to prove that one species evolved from another degree of certainty.

For example, protoceratopsians continue to appear in the fossil record after
the appearance of true ceratopsians. How can we tell where the ceratopsians
broke off the protoceratopsian line? So far as I know, we can't (at least
not without a lot more "in-between" species). All we can say with any
certainty is that they had a common anscestor. It could be that
Protoceratops itself is that common ancestor, but if that is the case the
Clade definition is still valid.

Now, my gripe with cladistics is definitions such as "All archosaurs closer
to birds than to crocodiles". This leaves some doubt over whether they had a
common ancestor (other than the common ancestor of the archosaurs itself).

James Shields  -  jshields@iol.ie  -  http://www.iol.ie/~jshields
-------------------------------------------------------------------------------
And when the ark was finished Noah said unto Elvis, "What do you reckin?"
And Elvis checked out his own cabin and shook his head saying "poky".
And so did they knock several walls through and install a jaccuzzi.
And when it was all done Noah scratched his beard and said, "We don't have
room for all the animals now."
And Elvis perused the livestock list and in his wisdom said, "Lose the
dinosaurs."
        -Robert Rankin, The Suburban Book of the Dead